Magnetochemistry

14 pages, 2858 KiB

Open AccessArticle

Nonlinear Electromagnetic Properties of Thinfilm Nanocomposites (CoFeZr)_x(MgF₂)_100−x

by Evelina P. Domashevskaya, Sergey A. Ivkov, Pavel V. Seredin, Dmitry L. Goloshchapov, Konstantin A. Barkov, Stanislav V. Ryabtsev, Yrii G. Segal, Alexander V. Sitnikov and Elena A. Ganshina

Magnetochemistry 2023, 9(6), 160; https://doi.org/10.3390/magnetochemistry9060160 - 20 Jun 2023

Viewed by 826

Abstract

The aim of this work is a comprehensive study of the effect of variable atomic composition and structural-phase state of (CoFeZr)_x(MgF₂)_100−x nanocomposites (NCs) on their nonlinear electronic and magnetic/magneto-optical properties. Micrometer-thick nanocomposite layers on the glass substrates were [...] Read more.

The aim of this work is a comprehensive study of the effect of variable atomic composition and structural-phase state of (CoFeZr)_x(MgF₂)_100−x nanocomposites (NCs) on their nonlinear electronic and magnetic/magneto-optical properties. Micrometer-thick nanocomposite layers on the glass substrates were obtained by ion-beam sputtering of a composite target in the argon atmosphere in a wide range of compositions x = 9–51 at·%. The value of the resistive percolation threshold, x_per = 34 at·%, determined from the concentration dependencies of the electrical resistance of NCs, coincides with the beginning of nucleation of metallic nanocrystals CoFeZr in MgF₂ dielectric matrix. The absolute value of maximum magnetoresistance of NCs is 2.4% in a magnetic field of 5.5 kG at x = 25 at·%, up to the percolation threshold. Two maxima appear in the concentration dependencies of magneto-optical transversal Kerr effect, one of which, at x = 34 at·%, corresponds to the formation of CoFeZr alloy nanocrystals of a hexagonal structure, and the second one at x = 45 at·% corresponds to the phase transition of nanocrystals from a hexagonal to a cubic body-centered structure. The magnetic percolation threshold in (CoFeZr)_x(MgF₂)_100−x system at x_fm = 34 at·%, with the appearance of a hysteresis loop and a coercive force of H_c ≈ 8 Oe, coincides with the resistive percolation threshold x_per = 34 at·%. Concentration dependence of the coercive force showed that at low contents of metallic alloy x < 30 at·%, NCs are superparamagnetic (H_c = 0). With an increase of the alloy content, in the region of magnetic and resistive percolation thresholds, NCs exhibit a magnetically soft ferromagnetic character and do not change it far beyond the percolation threshold, with the maximum value of the coercive force H_c < 30 Oe. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Magnetic and Magnetoelectric Materials)

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12 pages, 2573 KiB

Open AccessArticle

The Organic Ammonium Counterion Effect on Slow Magnetic Relaxation of the [Er(hfac)₄]⁻ Complexes

by Tatiana G. Prokhorova, Denis V. Korchagin, Gennady V. Shilov, Alexei I. Dmitriev, Mikhail V. Zhidkov and Eduard B. Yagubskii

Magnetochemistry 2023, 9(6), 159; https://doi.org/10.3390/magnetochemistry9060159 - 16 Jun 2023

Viewed by 849

Abstract

The first mononuclear anionic erbium complex [Er(hfac)₄]⁻ (hfac = hexafluoroacetylacetone) with an organic ammonium cation [(CH₃)₄N⁺] as the counterion was synthesized and structurally and magnetically characterized. The coordination geometries around the Er ions are [...] Read more.

The first mononuclear anionic erbium complex [Er(hfac)₄]⁻ (hfac = hexafluoroacetylacetone) with an organic ammonium cation [(CH₃)₄N⁺] as the counterion was synthesized and structurally and magnetically characterized. The coordination geometries around the Er ions are square antiprisms with pseudo-D_4d symmetry. The complex shows distinct field-induced slow magnetization relaxation, which is described by a combination of Orbach (U_eff/k_B~28.54(8) K.) and direct mechanisms. Quantum chemical calculations were performed to analyze the magnetic properties of the complex under consideration. Full article

(This article belongs to the Section Molecular Magnetism)

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Graphical abstract

19 pages, 13944 KiB

Open AccessFeature PaperArticle

Dynamic Footprints of the Specific Artificial Spin Ice Microstate on Its Spin Waves

by Pietro Micaletti and Federico Montoncello

Magnetochemistry 2023, 9(6), 158; https://doi.org/10.3390/magnetochemistry9060158 - 16 Jun 2023

Cited by 1 | Viewed by 1228

Abstract

We present a micromagnetic investigation of the spin dynamics at remanence (zero applied field) in a periodic square artificial spin ice (ASI) prepared four different microstates (i.e., with zero, two or four magnetic charges at the vertex). The ASI elements consist of permalloy [...] Read more.

We present a micromagnetic investigation of the spin dynamics at remanence (zero applied field) in a periodic square artificial spin ice (ASI) prepared four different microstates (i.e., with zero, two or four magnetic charges at the vertex). The ASI elements consist of permalloy elliptical dots with a fixed long axis, and a variable width and interdot separation. For each vertex configuration, we compute the equilibrium ground state at zero applied field by relaxing a previously set magnetic configuration (microstate). After the excitation of such ground state, we perform a Fourier analysis obtaining frequency spectra and space phase profiles. We discuss the behavior of the spectra in changing the system’s microstate and geometry, with reference to the spin mode space profiles, magnetization configuration, and effective internal field. Our results draw a correlation between ASI macrospin orientation at vertex and a few important dynamic properties like a phase-shift in the mode profiles or the frequency gap between the edge and fundamental modes. We suggest a few specific experiments to validate of our predictions, as well as applications in the field of interferometric magnonic devices. We believe that our results can help, from the fabrication stage, in tailoring the appropriate ASI geometry for specific application purposes. Full article

(This article belongs to the Special Issue Spin Waves in Magnonic Crystals and Hybrid Ferromagnetic Structures)

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14 pages, 3008 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Reduction of Oxidizable Pollutants in Waste Water from the Wadi El Bey River Basin Using Magnetic Nanoparticles as Removal Agents

by Hajer Tlili, Anis Elaoud, Nedra Asses, Karima Horchani-Naifer, Mounir Ferhi, Gerardo F. Goya and Jesús Antonio Fuentes-García

Magnetochemistry 2023, 9(6), 157; https://doi.org/10.3390/magnetochemistry9060157 - 14 Jun 2023

Cited by 3 | Viewed by 1775

Abstract

Many of the current strategies for removing pollutants from water are based on nanomaterials and nanotechnology. Lower values of Biological Oxygen Demand (BOD₅) and Chemical Oxygen Demand (COD) in water results in reduction in the amount of oxidizable pollutants. We present [...] Read more.

Many of the current strategies for removing pollutants from water are based on nanomaterials and nanotechnology. Lower values of Biological Oxygen Demand (BOD₅) and Chemical Oxygen Demand (COD) in water results in reduction in the amount of oxidizable pollutants. We present a study on the reduction of COD and BOD₅ in water from Wadi El Bey River (Tunisia), using magnetite nanoparticles (MNPs) and magnetic fields. The COD and BOD₅ removal reached values higher than 50% after 60 min, with optimum efficiency at pH values of ≈8 and for MNPs concentrations of 1 g/L. The use of a permanent magnetic field (0.33 T) showed an increase of COD and BOD₅ removal from 61% to 76% and from 63% to 78%, respectively. This enhancement is discussed in terms of the MNPs coagulation induced by the magnetic field and the adsorption of ionic species onto the MNPs surface due to Fe₃O₄ affinity. Full article

(This article belongs to the Section Magnetic Nanospecies)

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39 pages, 15083 KiB

Open AccessReview

Ferrite Nanoparticles as Catalysts in Organic Reactions: A Mini Review

by Nilima Maji and Harmanjit Singh Dosanjh

Magnetochemistry 2023, 9(6), 156; https://doi.org/10.3390/magnetochemistry9060156 - 14 Jun 2023

Cited by 4 | Viewed by 3175

Abstract

Ferrites have excellent magnetic, electric, and optical properties that make them an indispensable choice of material for a plethora of applications, such as in various biomedical fields, magneto–optical displays, rechargeable lithium batteries, microwave devices, internet technology, transformer cores, humidity sensors, high-frequency media, magnetic [...] Read more.

Ferrites have excellent magnetic, electric, and optical properties that make them an indispensable choice of material for a plethora of applications, such as in various biomedical fields, magneto–optical displays, rechargeable lithium batteries, microwave devices, internet technology, transformer cores, humidity sensors, high-frequency media, magnetic recordings, solar energy devices, and magnetic fluids. Recently, magnetically recoverable nanocatalysts are one of the most prominent fields of research as they can act both as homogeneous and heterogenous catalysts. Nano-ferrites provide a large surface area for organic groups to anchor, increase the product and decrease reaction time, providing a cost-effective method of transformation. Various organic reactions were reported, such as the photocatalytic decomposition of a different dye, alkylation, dehydrogenation, oxidation, C–C coupling, etc., with nano-ferrites as a catalyst. Metal-doped ferrites with Co, Ni, Mn, Cu, and Zn, along with the metal ferrites doped with Mn, Cr, Cd, Ag, Au, Pt, Pd, or lanthanides and surface modified with silica and titania, are used as catalysts in various organic reactions. Metal ferrites (MFe₂O₄) act as a Lewis acid and increase the electrophilicity of specific groups of the reactants by accepting electrons in order to form covalent bonds. Ferrite nanocatalysts are easily recoverable by applying an external magnetic field for their reuse without significantly losing their catalytic activities. The use of different metal ferrites in different organic transformations reduces the catalyst overloading and, at the same time, reduces the use of harmful solvents and the production of poisonous byproducts, hence, serving as a green method of chemical synthesis. This review provides insight into the application of different ferrites as magnetically recoverable nanocatalysts in different organic reactions and transformations. Full article

(This article belongs to the Special Issue Environmental Applications of Magnetic Nanoparticles and Nanocomposites)

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16 pages, 2583 KiB

Open AccessEditor’s ChoiceArticle

Spin Frustrated Pyrazolato Triangular Cu^II Complex: Structure and Magnetic Properties, an Overview

by Walter Cañón-Mancisidor, Patricio Hermosilla-Ibáñez, Evgenia Spodine, Verónica Paredes-García, Carlos J. Gómez-García and Diego Venegas-Yazigi

Magnetochemistry 2023, 9(6), 155; https://doi.org/10.3390/magnetochemistry9060155 - 11 Jun 2023

Viewed by 1375

Abstract

The synthesis and structural characterization of a new triangular Cu₃–μ₃OH pyrazolato complex of formula, [Cu₃(μ₃−OH)(pz)₃(Hpz)₃][BF₄]₂ (1−Cu₃), Hpz = pyrazole, is presented. The triangular unit forms [...] Read more.

The synthesis and structural characterization of a new triangular Cu₃–μ₃OH pyrazolato complex of formula, [Cu₃(μ₃−OH)(pz)₃(Hpz)₃][BF₄]₂ (1−Cu₃), Hpz = pyrazole, is presented. The triangular unit forms a quasi-isosceles triangle with Cu–Cu distances of 3.3739(9), 3.3571(9), and 3.370(1) Å. This complex is isostructural to the hexanuclear complex [Cu₃(μ₃−OH)(pz)₃(Hpz)₃](ClO₄)₂]₂ (QOPJIP). A comparative structural analysis with other reported triangular Cu₃–μ₃OH pyrazolato complexes has been carried out, showing that, depending on the pyrazolato derivative, an auxiliary ligand or counter-anion can affect the nuclearity and/or the dimensionality of the system. The magnetic properties of 1−Cu₃ are analyzed using experimental data and DFT calculation. A detailed analysis was performed on the magnetic properties, comparing experimental and theoretical data of other molecular triangular Cu₃–μ₃OH complexes, showing that the displacement of the μ₃−OH⁻ from the Cu₃ plane, together with the type of organic ligands, influences the nature of the magnetic exchange interaction between the spin-carrier centers, since it affects the overlap of the magnetic orbitals involved in the exchange pathways. Finally, a detailed comparison of the magnetic properties of 1−Cu₃ and QOPJIP was carried out, which allowed us to understand the differences in their magnetic properties. Full article

(This article belongs to the Special Issue Symmetry and Geometry, Key Parameters in 3d and 4f Molecular Magnetism)

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17 pages, 4837 KiB

Open AccessArticle

Magneto-Structural Analysis of Hydroxido-Bridged Cu^II₂ Complexes: Density Functional Theory and Other Treatments

by Debpriyo Goswami, Shanti Gopal Patra and Debashis Ray

Magnetochemistry 2023, 9(6), 154; https://doi.org/10.3390/magnetochemistry9060154 - 10 Jun 2023

Viewed by 1232

Abstract

A selection of dimeric Cu(II) complexes with bidentate N,N′ ligands with the general formula [Cu(L)(X)(μ-OH)]₂·nH₂O and [Cu(L)(μ-OH)]₂X₂·nH₂O were magneto-structurally analyzed using the Density Functional Theory (DFT). A Broken Symmetry-Density [...] Read more.

A selection of dimeric Cu(II) complexes with bidentate N,N′ ligands with the general formula [Cu(L)(X)(μ-OH)]₂·nH₂O and [Cu(L)(μ-OH)]₂X₂·nH₂O were magneto-structurally analyzed using the Density Functional Theory (DFT). A Broken Symmetry-Density Functional Theory (BS-DFT) study was undertaken for these complexes with relevant decomposition schemes that gave insight into the effect of the nature of the ligand and coordination environment on the DFT-predicted coupling constants (J). The impact of the spin population, which correlates well with the Cu-O-Cu bridging angles and the calculated coupling constant (J) values, was studied. The models were further refined using a complete active space self-consistent field (CASSCF) while expanding the active space from 2 orbitals 2 electrons (2,2) to 10 orbitals 18 electrons (18,10). These models were approximated using multireference methods (n-electron valence state perturbation theory and difference dedicated configuration interaction), and a better approximation of J values was found as expected. Orbitals involved in the superexchange pathway were also visualized. Full article

(This article belongs to the Special Issue Advances in Magnetostructural Correlation)

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18 pages, 3251 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Band Structure Evolution during Reversible Interconversion between Dirac and Standard Fermions in Organic Charge-Transfer Salts

by Ryuhei Oka, Keishi Ohara, Kensuke Konishi, Ichiro Yamane, Toshihiro Shimada and Toshio Naito

Magnetochemistry 2023, 9(6), 153; https://doi.org/10.3390/magnetochemistry9060153 - 09 Jun 2023

Cited by 3 | Viewed by 1816

Abstract

Materials containing Dirac fermions (DFs) have been actively researched because they often alter electrical and magnetic properties in an unprecedented manner. Although many studies have suggested the transformation between standard fermions (SFs) and DFs, the non-availability of appropriate samples has prevented the observation [...] Read more.

Materials containing Dirac fermions (DFs) have been actively researched because they often alter electrical and magnetic properties in an unprecedented manner. Although many studies have suggested the transformation between standard fermions (SFs) and DFs, the non-availability of appropriate samples has prevented the observation of the transformation process. We observed the interconversion process of DFs and SFs using organic charge-transfer (CT) salts. The samples are unique in that the constituents (the donor D and acceptor A species) are particularly close to each other in energy, leading to the temperature- and D-A-combination-sensitive CT interactions in the solid states. The three-dimensional weak D–A CT interactions in low-symmetry crystals induced the continuous reshaping of flat-bottomed bands into Dirac cones with decreasing temperature; this is a characteristic shape of bands that converts the behavior of SFs into that of DFs. Based on the first-principles band structures supported by the observed electronic properties, round-apex-Dirac-cone-like features appear and disappear with temperature variation. These band-structure snapshots are expected to add further detailed understanding to the related research fields. Full article

(This article belongs to the Special Issue Functional Molecular Materials Insights—a Themed Issue in Honour of Professor Manuel Almeida on the Occasion of His 70th Birthday)

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9 pages, 986 KiB

Open AccessArticle

Some Magnetic Properties and Magnetocaloric Effects in the High-Temperature Antiferromagnet YbCoC₂

by Denis Alexandrovich Salamatin, Vladimir Nikolaevich Krasnorussky, Mariya Viktorovna Magnitskaya, Alexei Valeryevich Semeno, Alexander Vladimirovich Bokov, Atanas Velichkov, Zbigniew Surowiec and Anatoly Vasilyevich Tsvyashchenko

Magnetochemistry 2023, 9(6), 152; https://doi.org/10.3390/magnetochemistry9060152 - 08 Jun 2023

Cited by 1 | Viewed by 1066

Abstract

The YbCoC₂ compound, which crystallizes in a base-centered orthorhombic unit cell in the

A m m 2

space group CeNiC₂ structure, is unique among Yb-based compounds due to the highest magnetic ordering temperature of

T_{N} = 27

K. Magnetization measurements [...] Read more.

The YbCoC₂ compound, which crystallizes in a base-centered orthorhombic unit cell in the

A m m 2

space group CeNiC₂ structure, is unique among Yb-based compounds due to the highest magnetic ordering temperature of

T_{N} = 27

K. Magnetization measurements have made it possible to plot the H-T magnetic phase diagram and determine the magnetocaloric effect of this recently discovered high-temperature heavy-fermion compound, YbCoC₂. YbCoC₂ undergoes spin transformation to the spin-polarized state through a metamagnetic transition in an external magnetic field. The transition is found to be of the first order. The dependencies of magnetic entropy change

Δ S_{m} (T)

—have segments with positive and negative magnetocaloric effects for

Δ H \leq 6

T. For

Δ H = 9

T, the magnetocaloric effect becomes positive, with a maximum

Δ S_{m} (T)

value of 4.1 J (kg K)⁻¹ at

T_{N}

and a refrigerant capacity value of 56.6 J kg⁻¹. Full article

(This article belongs to the Special Issue Synthetic, Natural and Natural-Synthetic Hybrid Magnetic Structures: Technology and Application)

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11 pages, 3320 KiB

Open AccessArticle

The Adsorption Performance of Porous Activated Carbons Prepared from Iron (II) Precursors Precipitated on the Porous Carbon Matrix Thermolysis

by Alexander Kalenskii, Aleksey Ivanov, Dmitriy Sevostyanov, Alexander Zvekov and Alexander Krechetov

Magnetochemistry 2023, 9(6), 151; https://doi.org/10.3390/magnetochemistry9060151 - 08 Jun 2023

Viewed by 1002

Abstract

The creation of new compounds featuring high adsorption and catalytic performance with magnetic properties of the material is one of the important fields of magnetochemistry. The typical synthetic schemes of magnetic carbonaceous adsorbents are rather complicated due to the use of inert atmosphere [...] Read more.

The creation of new compounds featuring high adsorption and catalytic performance with magnetic properties of the material is one of the important fields of magnetochemistry. The typical synthetic schemes of magnetic carbonaceous adsorbents are rather complicated due to the use of inert atmosphere and difficult wet methods of magnetite precipitation. The arising experimental issues prevent industrial production of magnetically activated carbons. In order to overcome these obstacles, we suggested a novel approach to porous carbons: magnetite composite synthesis based on iron (II) salt precipitation on porous carbon and subsequent thermolysis. We facilitated the process at the stage of the material washing. The synthetic route used is simple and can be applied industrially. The present paper is focused on the adsorption performance of a product prepared from commercial activated carbons BAU-A and AG-3. The porous structure was studied with low-temperature nitrogen adsorption that revealed surface area decreased by 26% in the case of BAU-A and 40% in the case of AG-3 with an increase in mesopore volume. Phenol and nitrobenzene adsorption from water solution was tested with magnetic carbon prepared from BAU-A. The adsorption isotherms obtained are described well using the Langmuir model. The limiting adsorption value in the case of magnetic porous carbon is lower than in the case of pristine carbon. The relative decrease in limiting adsorption value is close to the relative decrease in the specific surface area. The adsorption constant remains the same, showing that adsorption centers of phenol and nitrobenzene are the same for porous magnetic carbon and its activated carbon precursor. Thus, we showed in the present study that the magnetically activated carbons we developed almost retain the adsorption performance of their activated carbon precursors. Full article

(This article belongs to the Special Issue Advances in Magnetic Behavior of Graphite and Carbon Materials)

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7 pages, 350 KiB

Open AccessArticle

Driving a Molecular Spin-Peierls System into a Short Range Ordered State through Chemical Substitution

by Adam Berlie, Ian Terry and Marek Szablewski

Magnetochemistry 2023, 9(6), 150; https://doi.org/10.3390/magnetochemistry9060150 - 08 Jun 2023

Viewed by 858

Abstract

Chemically altering molecules can have dramatic effects on the physical properties of a series of very similar molecular compounds. A good example of this is within the quasi-1D spin-Peierls system potassium TCNQ (TCNQ = 7,7,8,8-tetracyanoqunidimethane), where substitution of TCNQF

_{4}

for TCNQ has [...] Read more.

Chemically altering molecules can have dramatic effects on the physical properties of a series of very similar molecular compounds. A good example of this is within the quasi-1D spin-Peierls system potassium TCNQ (TCNQ = 7,7,8,8-tetracyanoqunidimethane), where substitution of TCNQF

_{4}

for TCNQ has a dramatic effect on the 1D interactions, resulting in a drop in the corresponding spin-Peierls transition temperature. Within this work, we extend the investigation to potassium TCNQBr

_{2}

, where only two protons of TCNQ can be substituted with bromine atoms due to steric constraints. The new system exhibits evidence for a residual component of the magnetism when probed via magnetic susceptibility measurements and muon spin spectroscopy. The observations suggest that the system is dominated by short range, and potentially disordered, correlations within the bulk phase. Full article

(This article belongs to the Special Issue Functional Molecular Materials Insights—a Themed Issue in Honour of Professor Manuel Almeida on the Occasion of His 70th Birthday)

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14 pages, 3538 KiB

Open AccessFeature PaperArticle

From Micro to Nano: Grinding Natural Magnetite Ore for Microalgae Harvesting

by Michael Schobesberger, Simone Helmhagen, Stefan Mende, Sonja Berensmeier and Paula Fraga-García

Magnetochemistry 2023, 9(6), 149; https://doi.org/10.3390/magnetochemistry9060149 - 05 Jun 2023

Viewed by 1709

Abstract

Microalgae represent a promising feedstock for sustainable biomass and energy. The low cell concentration after cultivation, however, limits the current application fields. Magnetic microalgae harvesting is a recent approach to overcome the economic limitations of exploiting this natural resource. Accordingly, different particle types [...] Read more.

Microalgae represent a promising feedstock for sustainable biomass and energy. The low cell concentration after cultivation, however, limits the current application fields. Magnetic microalgae harvesting is a recent approach to overcome the economic limitations of exploiting this natural resource. Accordingly, different particle types have been applied, mainly synthetically produced magnetic nanoparticles, though none on an industrial scale. Particle sizes between a few micrometers and a few nanometers have not been tested. We expected 200–500 nm to be advantageous for harvesting and as a compromise between the highly available surface and good separation properties. However, this intermediate magnetite particle size between the micro- and nano-scale cannot be reached via chemical synthesis. Therefore, we ground natural magnetite ore in a planetary ball mill and an agitator bead mill producing particles in the targeted size range. Applying ore particles ground from ~6 µm to 250 nm yields harvesting efficiencies comparable to synthetically produced nanoparticles (Ø ~ 10 nm), with only half the BET surface. Complete harvesting of saline microalgae Microchloropsis salina is possible with ground particles at alkaline pH. We demonstrate the feasibility of a harvesting process with natural, low-cost, easily separable, and readily available magnetite ore particles as a promising step towards exploiting valuable microalgal products in life sciences. Full article

(This article belongs to the Special Issue Magnetic Separation: Principles, Devices, and Applications)

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16 pages, 715 KiB

Open AccessEditor’s ChoiceReview

Nuclear Dipole Moments and Shielding Constants of Light Nuclei Measured in Magnetic Fields

by Włodzimierz Makulski, Mateusz A. Słowiński and Piotr Garbacz

Magnetochemistry 2023, 9(6), 148; https://doi.org/10.3390/magnetochemistry9060148 - 02 Jun 2023

Cited by 1 | Viewed by 1301

Abstract

Nuclear magnetic resonance (NMR) is a branch of spectroscopy commonly used for identifying the chemical structure of various materials. One of the areas in which NMR provides accurate data is the determination of nuclear magnetic moments. This work reviews NMR experiments with the [...] Read more.

Nuclear magnetic resonance (NMR) is a branch of spectroscopy commonly used for identifying the chemical structure of various materials. One of the areas in which NMR provides accurate data is the determination of nuclear magnetic moments. This work reviews NMR experiments with the nuclei of light elements in simple molecules. Since nuclear shielding constants from up-to-date quantum calculations are now available, very accurate dipole moments of many nuclei can be determined. Recent experimental measurements of ¹H, ²H, ³H, ³He, ⁶Li, ⁷Li, ⁹Be, ¹⁰B, and ¹¹B nuclear magnetic moments and the appropriate theoretical predictions are presented and commented upon. Several achievements in this field using different methodologies, such as NMR spectroscopy, molecular beam experiments, and the Penning trap method are reported. Full article

(This article belongs to the Section Magnetic Resonances)

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13 pages, 1901 KiB

Open AccessFeature PaperArticle

Substitution Effects in Spin-Polarized (Cr_4-xFe_x)_0.5AC (A = Ge, Si, Al) MAX Phases

by Natalja A. Fedorova, Alena V. Kovaleva, Julia S. Olshevskaya, Daria A. Ivanova, Victoria V. Kozak, Alexander A. Shubin, Anton S. Tarasov, Sergey N. Varnakov, Sergei G. Ovchinnikov, Evgeniya M. Moshkina, Olga A. Maximova, Pavel V. Avramov and Felix N. Tomilin

Magnetochemistry 2023, 9(6), 147; https://doi.org/10.3390/magnetochemistry9060147 - 30 May 2023

Cited by 1 | Viewed by 1173

Abstract

The use of spintronic devices with a tunable magnetic order on small scales is highly important for novel applications. The MAX phases containing transition metals and/or magnetic ion-substituted lattices attract a lot of attention. In this study, the magnetic and electronic properties of [...] Read more.

The use of spintronic devices with a tunable magnetic order on small scales is highly important for novel applications. The MAX phases containing transition metals and/or magnetic ion-substituted lattices attract a lot of attention. In this study, the magnetic and electronic properties of (Cr_4-xFe_x)_0.5AC (A = Ge, Si, Al) compounds were predicted and investigated within the density functional theory. It was established that single-substituted (Cr₃Fe₁)_0.5AC (A = Ge, Si, Al) lattices are favorable in terms of energy. An analysis of the magnetic states of the MAX phases demonstrated that their spin order changes upon substitution of iron atoms for chromium ones. It was found that mostly the (Cr_4-xFe_x)_0.5GeC and (Cr_4-xFe_x)_0.5AlC lattices acquire a ferrimagnetic state in contrast to (Cr_4-xFe_x)_0.5SiC for which the ferromagnetic spin order dominates. It was pointed out that the atomic substitution could be an efficient way to tune the magnetic properties of proposed (Cr_4-xFe_x)_0.5AC (A = Ge, Si, Al) MAX phases. Full article

(This article belongs to the Section Spin Crossover and Spintronics)

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12 pages, 7794 KiB

Open AccessEditor’s ChoiceArticle

Research on the Surfactant-Assisted Synthesis of MnZn Ferrite Precursor Powders

by Zhanyuan Xu, Wei Zhao, Jiefu Liu and Jinglian Fan

Magnetochemistry 2023, 9(6), 146; https://doi.org/10.3390/magnetochemistry9060146 - 30 May 2023

Viewed by 1129

Abstract

MnZn ferrite precursor powders were prepared by the nano in situ composite method. Three surfactants, which include polyethylene glycol 400 (PEG-400), cetyltrimethyl ammonium bromide (CTAB), and sodium dodecyl sulfate (SDS), were usedM and the impact of the surfactants on the precursor sol solutions [...] Read more.

MnZn ferrite precursor powders were prepared by the nano in situ composite method. Three surfactants, which include polyethylene glycol 400 (PEG-400), cetyltrimethyl ammonium bromide (CTAB), and sodium dodecyl sulfate (SDS), were usedM and the impact of the surfactants on the precursor sol solutions and precursor powders was studied. X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy, Raman spectroscopy, a field emission scanning electron microscope (FE-SEM), a transmission electron microscope (TEM), a Zeta potential meter, a BET surface analyzer, and a vibrational sample magnetometer (VSM) were used to characterize the precursor sol solutions and the precursor powders. The results showed that these surfactants can improve the dispersion state and Zeta potentials of sol particles and increase the specific surface areas of the precursor powders. Moreover, the precursor powders were composed of MnZn ferrite, and some were amorphous. CTAB was the optimum surfactant and the zeta potential of the sol particles and the specific surface area of the precursor powders named P-0.1CTAB are 10.7 mV and 129.07 m²/g, respectively. In addition, the nano-particles that were made up of the P-0.1CTAB precursor powders had smaller sizes and more uniform particle distributions than the others. The magnetic properties’ improvement was attributed to the addition of surfactants, and CTAB is the optimal type. In addition, the novel nano in situ composite method will inspire fresh thinking and investigation into the research of ferrite. Full article

(This article belongs to the Special Issue Advances in Soft Magnetic Materials)

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12 pages, 19112 KiB

Open AccessArticle

Fabrication and Soft Magnetic Properties of Fe–Si–Cr Composites with Double-Insulating Layers Suitable for High-Frequency Power Applications

by Zhenyi Huang, Huaqin Huang, Hao He, Kaixuan Li, Zhaoyang Wu and Rui Wang

Magnetochemistry 2023, 9(6), 145; https://doi.org/10.3390/magnetochemistry9060145 - 30 May 2023

Cited by 1 | Viewed by 1109

Abstract

Soft magnetic composites (SMCs) are composed of alloy materials with the core and insulating layers as the shell. These composites exhibit high saturation magnetic sensitivity and low hysteresis loss, making them a promising material for various applications. The investigation of double layers is [...] Read more.

Soft magnetic composites (SMCs) are composed of alloy materials with the core and insulating layers as the shell. These composites exhibit high saturation magnetic sensitivity and low hysteresis loss, making them a promising material for various applications. The investigation of double layers is considered valuable as it can effectively address the issues of low resistivity and high dynamic loss that arise from non-uniform insulating layers in SMCs. In this study, Fe-Si-Cr/SiO₂ particles with a core–shell heterostructure were produced via chemical vapor deposition (CVD). The Fe-Si-Cr/SiO₂ materials were coated with different weight percentages (1–6%) of sodium silicate (SS). Subsequently, Fe-Si-Cr-based SMCs were synthesized through high-pressure molding and heat treatment. The effect of the SS weight percentage on microscopic changes and magnetic characteristics was investigated. These findings indicated that a concentration of 4 wt% of SS was the most effective at enhancing magnetic characteristics. The resultant SMCs exhibited high resistivity (21.07 mΩ·cm), the lowest total loss (P_{10 mt/300 kHz} of 44.23 W/kg), a relatively high saturation magnetization (181.8 emu/g), and permeability (35.9). Furthermore, it was observed that the permeability exhibited stabilization at lower frequencies. According to these findings, the combination of CVD and double layers could lead to the further development of SMCs in a variety of applications. Full article

(This article belongs to the Special Issue Advances in Soft Magnetic Materials)

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12 pages, 3449 KiB

Open AccessArticle

Magnetism and Exchange Bias Properties in Ba₂ScRuO₆

by Prachi Mohanty, Sourav Marik and Ravi Prakash Singh

Magnetochemistry 2023, 9(6), 144; https://doi.org/10.3390/magnetochemistry9060144 - 29 May 2023

Cited by 2 | Viewed by 1110

Abstract

This paper presents structural, detailed magnetic, and exchange bias studies in polycrystalline Ba

_{2}

ScRuO

_{6}

synthesized at ambient pressure. In contrast to its strontium analogue, this material crystallizes in a 6L hexagonal structure with space group P

\bar{3}

m1. The Rietveld [...] Read more.

This paper presents structural, detailed magnetic, and exchange bias studies in polycrystalline Ba

_{2}

ScRuO

_{6}

synthesized at ambient pressure. In contrast to its strontium analogue, this material crystallizes in a 6L hexagonal structure with space group P

\bar{3}

m1. The Rietveld refinement using the room-temperature powder XRD pattern suggests a Ru-Sc disorder in the structure. The temperature variation of the DC electrical resistivity highlights a semiconducting behavior with the electron conduction corresponding to Mott’s 3D variable range hopping (VRH) model. The detailed magnetization measurements show that Ba

_{2}

ScRuO

_{6}

develops antiferromagnetic ordering at

T_{N}

≈ 9 K. Interestingly, below 9 K (T

_{N}

), the field-cooled magnetic field variation (FC) of the magnetization curves highlights an exchange bias effect in the sample. The exchange bias field reaches a maximum value of 1.24 kOe at 2 K. The exchange bias effect below the magnetic ordering temperature can be attributed to the inhomogeneous magnetic correlations due to the disorder in the structure. Remarkably, the appearance of a large exchange bias field in Ba

_{2}

ScRuO

_{6}

indicates that inhomogeneous hexagonal double perovskites are a promising class to explore new materials having potential applications in spintronics. Full article

(This article belongs to the Special Issue Editorial Board Members’ Collection Series: Magnetic and Magnetoelectric Materials)

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17 pages, 3303 KiB

Open AccessArticle

Study of Dynamic Viscoelasticity of a Mineral Oil-Based Magnetic Fluid

by Zhanxian Li, Yifei Guo, Hujun Wang, Chengyao Deng, Jiahao Dong, Zhongru Song and Zhenkun Li

Magnetochemistry 2023, 9(6), 143; https://doi.org/10.3390/magnetochemistry9060143 - 29 May 2023

Viewed by 1035

Abstract

Magnetic fluid is a field-responsive intelligent fluid, which has the flow characteristics of liquid and the elastic properties of solid. Because of its unique properties, it has a strong application prospect in the fields of magnetic soft robot, intelligent sensor, and so on. [...] Read more.

Magnetic fluid is a field-responsive intelligent fluid, which has the flow characteristics of liquid and the elastic properties of solid. Because of its unique properties, it has a strong application prospect in the fields of magnetic soft robot, intelligent sensor, and so on. Dynamic viscoelasticity is a significant index to investigate the performance of magnetic fluid in the application process. In this paper, the dynamic viscoelasticity of a homemade mineral oil-based magnetic fluid was investigated under oscillatory shear experimental conditions using an MCR302 rheometer, and the effects of different temperatures and magnetic fields on the dynamic viscoelasticity were examined. Amplitude sweeps tests showed that the value of the storage modulus remained constant within the linear viscoelastic region (LVE) and the stable structure was not destroyed. As the magnetic field strength increased or the temperature increased, the range of the linear viscoelastic zone decreased. At large amplitude, the loss modulus will first appear as a peak and then decrease. The frequency sweep experiment showed that the storage modulus and loss modulus increased with the increase in angular frequency, and the greater the magnetic field intensity, the longer the internal structure relaxation time. When the magnetic field was constant, the higher the temperature, the smaller the storage modulus and loss modulus of the magnetic fluid. At high temperature, the loss coefficient of mesmeric fluid was large, and the magnetic fluid was more viscous. The lower the temperature is, the smaller the loss coefficient of the magnetic fluid is, and the magnetic fluid is more pliant. The study of dynamic viscoelasticity of magnetic fluids lays the foundation for establishing the complete structure intrinsic relationship of magnetic fluids and provides guidance for the application of magnetic fluids in magnetic 3D printing, droplet robot, and smart wear. Full article

(This article belongs to the Section Applications of Magnetism and Magnetic Materials)

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13 pages, 398 KiB

Open AccessArticle

Magnetoelectric Coupling Effects in Tb-Doped BiFeO₃ Nanoparticles

by Iliana Apostolova, Angel Apostolov and Julia Wesselinowa

Magnetochemistry 2023, 9(6), 142; https://doi.org/10.3390/magnetochemistry9060142 - 26 May 2023

Cited by 2 | Viewed by 940

Abstract

The magnetic, electric, and optical properties in Tb-doped BiFeO₃ nanoparticles as functions of size and doping concentrations were investigated using a microscopic model, taking into account both linear and quadratic magnetoelectric (ME) coupling. We observed improved multiferroic properties and band-gap tuning. The [...] Read more.

The magnetic, electric, and optical properties in Tb-doped BiFeO₃ nanoparticles as functions of size and doping concentrations were investigated using a microscopic model, taking into account both linear and quadratic magnetoelectric (ME) coupling. We observed improved multiferroic properties and band-gap tuning. The magnetization and polarization increased with the decreased nanoparticle size and increased Tb-doping substitution x. The Neel temperature remained nearly unchanged whereas the Curie temperature was reduced with the increased x. There was doping-induced ME coupling. The dielectric constant is discussed as a function of the size, doping, and the magnetic field. The band gap decreased with the decreased size or increased Tb dopants due to competing effects of the compressive strain, oxygen defects on the surface, and Coulomb interactions. Increasing the Tb dopants and decreasing the nanoparticle size improved the ME effect. Full article

(This article belongs to the Special Issue Advances in Magnetic Nanomaterials and Nanostructures)

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17 pages, 3633 KiB

Open AccessArticle

Thermal Conductivity for p–(Bi, Sb)₂Te₃ Films of Topological Insulators

by Lidia N. Lukyanova, Yuri A. Boikov, Oleg A. Usov, Viacheslav A. Danilov, Igor V. Makarenko and Vasilii N. Petrov

Magnetochemistry 2023, 9(6), 141; https://doi.org/10.3390/magnetochemistry9060141 - 25 May 2023

Viewed by 964

Abstract

In this study, we investigated the temperature dependencies of the total, crystal lattice, and electronic thermal conductivities in films of topological insulators p–Bi_0.5Sb_1.5Te₃ and p–Bi₂Te₃ formed by discrete and thermal evaporation methods. The largest decrease [...] Read more.

In this study, we investigated the temperature dependencies of the total, crystal lattice, and electronic thermal conductivities in films of topological insulators p–Bi_0.5Sb_1.5Te₃ and p–Bi₂Te₃ formed by discrete and thermal evaporation methods. The largest decrease in the lattice thermal conductivity because of the scattering of long-wavelength phonons on the grain interfaces was observed in the films of the solid-solution p–Bi_0.5Sb_1.5Te₃ deposited by discrete evaporation on the amorphous substrates of polyimide without thermal treatment. It was shown that in the p–Bi_0.5Sb_1.5Te₃ films with low thermal conductivity, the energy dependence of the relaxation time is enhanced, which is specific to the topological insulators. The electronic thermal conductivity was determined by taking into account the effective scattering parameter in the relaxation time approximation versus energy in the Lorentz number calculations. A correlation was established between the thermal conductivity and the peculiarities of the morphology of the interlayer surface (0001) in the studied films. Additionally, the total κ and the lattice κ_L thermal conductivities decrease, while the number of grains and the roughness of the surface (0001) increase in unannealed films compared to annealed ones. It was demonstrated that increasing the thermoelectric figure of merit ZT in the p–Bi_0.5Sb_1.5Te₃ films formed by discrete evaporation on a polyimide substrate is determined by an increase in the effective scattering parameter in topological insulators due to enhancement in the energy dependence of the relaxation time. Full article

(This article belongs to the Special Issue Spin and Charge Transport in Novel Quantum and Topological Materials)

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13 pages, 2802 KiB

Open AccessFeature PaperArticle

Controlling the Magnetic Properties of La_0.9A_0.1Mn_0.9Cr_0.1O₃ (A: Li, K, Na) Powders and Ceramics by Alkali Ions Doping

by Paweł Głuchowski, Ruslan Nikonkov, Daniela Kujawa, Wiesław Stręk, Tomas Murauskas, Andrius Pakalniškis, Aivaras Kareiva, Andrii Yaremkevych, Olena Fesenko, Aliaksandr Zhaludkevich and Dmitry Karpinsky

Magnetochemistry 2023, 9(6), 140; https://doi.org/10.3390/magnetochemistry9060140 - 25 May 2023

Viewed by 1034

Abstract

Nanocrystalline La_0.9A_0.1Mn_0.9Cr_0.1O₃ (A: Li, K, Na) powders have been synthesized by combustion method. The powders were used to prepare ceramics by high-pressure low-temperature sintering technique. For all samples the structure, elemental composition and morphology [...] Read more.

Nanocrystalline La_0.9A_0.1Mn_0.9Cr_0.1O₃ (A: Li, K, Na) powders have been synthesized by combustion method. The powders were used to prepare ceramics by high-pressure low-temperature sintering technique. For all samples the structure, elemental composition and morphology were studied using X-ray diffraction (XRD), Raman spectroscopy, Energy-Dispersive X-ray Spectroscopy (EDS) and Scanning electron microscopy (SEM). Magnetic properties were studied using magnetometry methods and the valency changes of the cations after alkali ions doping were studied using X-ray photoelectron spectroscopy (XPS). The influence of the sintering pressure on the structural and magnetic properties of the manganites doped with different alkali ions and chromium was also investigated. Magnetization properties were studied as a function of sintering pressure and type of the dopant. Chemical doping with alkali ions as well as external pressure significantly changed the magnetic properties of the compounds. It was found that the magnetic properties of the manganites could be predictably modified through the use of a suitable dopant element. Full article

(This article belongs to the Special Issue Synthetic, Natural and Natural-Synthetic Hybrid Magnetic Structures: Technology and Application)

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11 pages, 2289 KiB

Open AccessArticle

Hydrothermal Synthesis and Magnetic Properties of Zn/Mn Oxides Nano Particles

by Izabela Kuryliszyn-Kudelska, Witold Dobrowolski, Monika Arciszewska, Branka Hadžić, Nebojsa Romčević, Maja Romčević, Daniel Sibera and Urszula Narkiewicz

Magnetochemistry 2023, 9(6), 139; https://doi.org/10.3390/magnetochemistry9060139 - 25 May 2023

Viewed by 1090

Abstract

The aim of this study was to investigate the magnetic properties of mixed nanocrystalline Zn/manganese oxide compounds synthesized by a hydrothermal method. These compounds are designed as (ZnO)_1−n(MnO)_n, where index n ranges from 0.05 to 0.60. The results of [...] Read more.

The aim of this study was to investigate the magnetic properties of mixed nanocrystalline Zn/manganese oxide compounds synthesized by a hydrothermal method. These compounds are designed as (ZnO)_1−n(MnO)_n, where index n ranges from 0.05 to 0.60. The results of magnetic measurements, including AC magnetic susceptibility as a function of temperature (up to 160 K) and frequency (from 7 Hz up to 9970 Hz), as well as DC magnetization in magnetic fields up to 9 T and temperature up to 50 K, are reported. We observed various types of magnetic behavior depending on the nominal weight content of MnO. Samples with a low nominal content (up to n = 0.10) of MnO exhibited Curie–Weiss behavior at higher temperatures. For samples with high nominal weight contribution (from n = 0.30 to 0.60), spin-glass-like or/and weak ferromagnetic behavior is observed. Full article

(This article belongs to the Special Issue Advances in Magnetic Nanomaterials and Nanostructures)

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19 pages, 3989 KiB

Open AccessFeature PaperArticle

Influence of Mn Doping on Local Spin Moments and Stacking Fault Energies in Co(Mn) Alloys

by Kayla Cole-Piepke, Prabandha Nakarmi, Alicia Koenig, Gregory B. Thompson, Tim Mewes, Claudia Mewes, Ronald Noebe and Alex Leary

Magnetochemistry 2023, 9(6), 138; https://doi.org/10.3390/magnetochemistry9060138 - 23 May 2023

Viewed by 977

Abstract

We report on the results of first principles calculations investigating the influences of Mn doping on the local moments and stacking fault energies (SFEs) in the Co

_{95.8}

Mn

_{4.2}

and Co

_{91.6}

Mn

_{8.4}

systems as compared to pure face-centered cubic Co. [...] Read more.

We report on the results of first principles calculations investigating the influences of Mn doping on the local moments and stacking fault energies (SFEs) in the Co

_{95.8}

Mn

_{4.2}

and Co

_{91.6}

Mn

_{8.4}

systems as compared to pure face-centered cubic Co. A supercell was developed to maintain periodicity in calculations, provide a simple relaxation mechanism, and allow for easy expansion to accommodate different concentrations of Mn. Calculations to determine the generalized SFE were performed on relaxed and non-relaxed systems in both ferromagnetic and nonmagnetic states. Analysis revealed fluctuations in the magnetic moments that are closely tied to the relaxation state and faulting state of the system. In the case of systems containing Mn, we observed a dependence of the SFE on the location of the Mn atom(s) within the supercell relative to the stacking fault interface and a strong induced magnetic moment for these atoms. Full article

(This article belongs to the Special Issue Advances in Magnetic Nanomaterials and Nanostructures)

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Magnetochemistry, Volume 9, Issue 6 (June 2023) – 23 articles

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