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A special issue of Nanomaterials (ISSN 2079-4991). This special issue belongs to the section "Inorganic Materials and Metal-Organic Frameworks".

Deadline for manuscript submissions: closed (30 September 2023) | Viewed by 16077

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Dr. Ovidiu Crisan

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National Institute for Materials Physics, 077125 Magurele, Romania
Interests: magnetic nanomaterials; exchange spring and exchange bias; spintronics; THz technologies
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Magnetic nanomaterials and nanoscale systems represent some of the most widely researched topics over recent decades. Recent breakthroughs in high-resolution imaging techniques, modern computing, and nanoelectronics have favoured an increase in interest in the quest for new materials and novel applications. Tailor-made nanoclusters and surface functionalized nanoparticles, multilayered thin films, as well as nanocomposite magnetic materials are widely researched and expected results will be of benefit to the future digitalized economy. In the search for new magnets, although computer modelling may provide hints for finding structures that minimize the internal energy, the control of nanoscale phenomena in real time remains an unsolved issue. Magnetic nanoparticles deserve special attention because of their extended applicability not only for data storage and nanoscale spintronics applications but also for healthcare. Medical researchers are actively seeking to develop improved tools for hyperthermia therapy or drug delivery.

This Special Issue is trying to gather a carefully selected compilation of original research papers to aid our understanding of and gain insights into magnetic properties, tailored magnetic materials, and surface functionalized nanoparticles. This issue also calls for papers addressing fundamental approaches to magnetism and spintronics, prediction of novel magnetic compounds, as well as application-specific materials such as magnets for use in extreme conditions of technological operations and nanomagnetic systems for biomedical use as drug delivery agents, hyperthermia therapy, and contrast enhancement in magnetic resonance imaging or gene sequencing, to name but a few.

Dr. Ovidiu Crisan
Guest Editor

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Keywords

nanocomposite magnets
surface functionalized nanoparticles, nanoscale magnetism
prediction of novel magnetic compounds
nanomagnetism and spintronics
tailor-made magnetic materials
exchange coupled magnets
magnets for extreme conditions of operation
nanomagnets for biomedical applications

Published Papers (10 papers)

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Research

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11 pages, 1076 KiB

Open AccessArticle

Remarkable Magnetic Properties in a Mn_73.6Ga_26.4 Alloy Produced via Out-of-Equilibrium Method

by Ovidiu Crisan and Alina Daniela Crisan

Nanomaterials 2023, 13(23), 3014; https://doi.org/10.3390/nano13233014 - 24 Nov 2023

Viewed by 628

Abstract

Rare-earth-free permanent magnets with the L1₀ phase are actively researched for their potential as a future class of magnetic materials, capable of operating at higher temperatures and in challenging corrosion environments such as renewable energy applications. Among these classes, MnGa shows potential, being cost effective and having interesting magnetic properties. A MnGa magnetic alloy, with composition Mn_73.6Ga_26.4 in atomic percent, was produced via the out-of-equilibrium method, and its structural and magnetic properties were assessed using X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED) and extended magnetic characterization. We show that the MnGa alloy submitted to thermal annealing in optimal conditions exhibits a two-phase microstructure, where small nanocrystals of tetragonal L1₀/D0₂₂ magnetic phase are embedded within a D0₁₉ MnGa matrix of a non-collinear antiferromagnetic nature. These co-existing, magnetically different phases produce an optimal set of promising magnetic properties, larger than the values reported in the literature for single-phase MnGa alloys and thin films. Such large values are explained by the exchange coupling between competing non-collinear magnetic sublattices of the D0₁₉ MnGa with the net moment of the small magnetic nanocrystals of tetragonal symmetry. Full article

(This article belongs to the Special Issue Current Research in Magnetic Nanomaterials: From Fundamentals towards Applications)

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14 pages, 14655 KiB

Open AccessEditor’s ChoiceArticle

Magnetic Properties and Microstructure of FePt(BN, X, C) (X = Ag, Re) Films

by Jai-Lin Tsai, Chun-Yu Sun, Jhih-Hong Lin, Yi-Yuan Huang and He-Ting Tsai

Nanomaterials 2023, 13(3), 539; https://doi.org/10.3390/nano13030539 - 29 Jan 2023

Cited by 1 | Viewed by 1574

Abstract

A sputtered FePt(BN, Re, C) film, here boron nitride (BN), was compared to a reference sample FePt(BN, Ag, C). Intrinsically, these films illustrate a high anisotropy field (H_k) and perpendicular magnetocrystalline anisotropy (K_u),although the reference sample shows a higher value (H_k = 69.5 kOe, K_u = 1.74 × 10⁷ erg/cm³) than the FePt(BN, Re, C) film (H_k = 66.9 kOe, K_u = 1.46 × 10⁷ erg/cm³). However, the small difference in the anisotropy constant (K2/K1) ratio presents a close tendency in the angular dependence of the switching field. Extrinsically, the out-of-plane coercivity for the reference sample is 32 kOe, which is also higher than the FePt(BN, Re, C) film (H_c = 27 kOe), and both films present lower remanence (Mr_(parallel)/Mr_{(perpendicular)} = 0.08~0.12), that is, the index for perpendicular magnetic anisotropy. The higher perpendicular magnetization for both films was due to highly (001) textured FePt films, which was also evidenced by the tight rocking width of 4.1°/3.0° for (001)/(002) X-ray diffraction peaks, respectively, and high-enough ordering degree. The reference sample was measured to have a higher ordering degree (S = 0.84) than FePt(BN, Re, C) (S = 0.63). As a result, the Ag segregant shows stronger ability to promote the ordering of the FePt film; however, the FePt(BN, Re, C) film still has comparable magnetic properties without Ag doping. From the surface and elemental composition analysis, the metallic Re atoms found in the FePt lattice result in a strong spin–orbital coupling between transition metal Fe (3d electron) and heavy metals (Re, Pt) (5d electron) and we conducted high magnetocrystalline anisotropy (K_u). Above is the explanation that the lower-ordered FePt(BN, Re, C) film still has high-enough Ku and out-of-plane Hc. Regarding the microstructure, both the reference sample and FePt(BN, Re, C) show granular structure and columnar grains, and the respective average grain size and distributions are 6.60 nm (12.5%) and 11.2 nm (15.9%). The average widths of the grain boundaries and the aspect ratio of the columnar grain height are 2.05 nm, 1.00 nm, 2.35 nm, and 1.70 nm, respectively. Full article

(This article belongs to the Special Issue Current Research in Magnetic Nanomaterials: From Fundamentals towards Applications)

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11 pages, 2312 KiB

Open AccessArticle

Nutation Excitations in the Gyrotropic Vortex Dynamics in a Circular Magnetic Nanodot

by Zukhra Gareeva and Konstantin Guslienko

Nanomaterials 2023, 13(3), 461; https://doi.org/10.3390/nano13030461 - 23 Jan 2023

Cited by 2 | Viewed by 1602

Abstract

A significant activity is devoted to the investigation of the ultrafast spin dynamic processes, holding a great potential for science and applications. However, a challenge of the understanding of the mechanisms of underlying spin dynamics in nanomaterials at pico- and femtosecond timescales remains under discussion. In this article, we explore the gyrotropic vortex dynamics in a circular soft magnetic nanodot, highlighting the impacts given by nutations in the high-frequency part of the dot spin excitation spectrum. Using a modified Thiele equation of the vortex core motion with a nutation term, we analyze the dynamic response of the vortex to an oscillating magnetic field applied in the dot plane. It is found that nutations affect the trajectory of the vortex core. Namely, we show that the directions of the vortex core motion in the low-frequency gyrotropic mode and the high-frequency nutation mode are opposite. The resonant frequencies of gyrotropic and nutational vortex core motions reveal themselves on different scales: gigahertz for the gyrotropic motion and terahertz for the nutations. We argue that the nutations induce a dynamic vortex mass, present estimates of the nutational mass, and conduct comparison with the mass appearing due to moving vortex interactions with spin waves and Doering domain wall mass. Full article

(This article belongs to the Special Issue Current Research in Magnetic Nanomaterials: From Fundamentals towards Applications)

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15 pages, 3037 KiB

Open AccessArticle

Assessing the Heat Generation and Self-Heating Mechanism of Superparamagnetic Fe₃O₄ Nanoparticles for Magnetic Hyperthermia Application: The Effects of Concentration, Frequency, and Magnetic Field

by O. M. Lemine, Saja Algessair, Nawal Madkhali, Basma Al-Najar and Kheireddine El-Boubbou

Nanomaterials 2023, 13(3), 453; https://doi.org/10.3390/nano13030453 - 22 Jan 2023

Cited by 8 | Viewed by 1941

Abstract

Magnetite nanoparticles (MNPs) exhibit favorable heating responses under magnetic excitation, which makes them particularly suited for various hyperthermia applications. Herein, we report the detailed self-heating mechanisms of MNPs prepared via the Ko-precipitation Hydrolytic Basic (KHB) methodology. The as-prepared MNPs were fully characterized using various spectroscopic techniques including transmission electron microscopy (TEM), dynamic light scattering (DLS), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), and vibrating sample magnetometry (VSM). MNPs exhibited stable 15 nm quasi-spherical small-sized particles, pure crystalline cubic Fe₃O₄ phases, high saturation magnetizations (Ms = ~40 emu·g⁻¹), and superparamagnetic behavior. In response to alternating magnetic fields (AMFs), these MNPs displayed excellent self-heating efficiencies with distinctive heating responses, even when minimal doses of MNPs were used. Heating efficacies and specific absorption rate (SAR) values as functions of concentration, frequency, and amplitude were systematically investigated. Remarkably, within only a few minutes, MNPs (2.5 mg/mL) showed a rapid dissipation of heat energy, giving a maximum intrinsic loss power (ILP) of 4.29 nHm²/kg and a SAR of 261 W/g. Hyperthermia temperatures were rapidly reached in as early as 3 min and could rise up to 80 °C. In addition, Rietveld refinement, Langevin, and linear response theory (LRT) models were studied to further assess the magnetic and heating mechanisms. The LRT model was used to determine the Néel relaxation time (τ_R = 5.41 × 10⁻⁷ s), which was compared to the Brownian relation time value (τ_B = 11 × 10⁻⁷ s), showing that both mechanisms are responsible for heat dissipated by the MNPs. Finally, the cytotoxicity assay was conducted on aqueous dispersions of MNPs, indicating their biocompatibility and low toxicity. Our results strongly suggest that the as-prepared Fe₃O₄ MNPs are promising vehicles for potential magnetically triggered biomedical hyperthermia applications. Full article

(This article belongs to the Special Issue Current Research in Magnetic Nanomaterials: From Fundamentals towards Applications)

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15 pages, 3943 KiB

Open AccessArticle

Different Stages of Phase Transformation in the Synthesis of Nanocrystalline Sr-Hexaferrite Powder Prepared by a Gaseous Heat Treatment and Re-Calcination Method

by Ramin Dehghan, Seyyed Ali Seyyed Ebrahimi, Zahra Lalegani and Bejan Hamawandi

Nanomaterials 2022, 12(21), 3714; https://doi.org/10.3390/nano12213714 - 22 Oct 2022

Cited by 1 | Viewed by 1040

Abstract

In this paper, the phase transformation in a gaseous heat treatment and re-calcination (GTR) process for preparing nanocrystalline Sr-hexaferrite powder using methane (CH₄) was studied. The process included gaseous heat treatment and subsequent re-calcination. Phase composition of the powder and its physical properties were changed significantly owing to formation of different intermediate phases. Sr-hexaferrite powder was prepared by the conventional route as the precursor. The results were represented in a phase transformation map that showed the intermediate phases and clarified the transformation path during the process. As evidenced by the map, the process had four general stages: decomposition of hexaferrite, reduction of iron oxides to pure iron, re-oxidation of iron, and re-formation of hexaferrite with different properties and structure. Full article

(This article belongs to the Special Issue Current Research in Magnetic Nanomaterials: From Fundamentals towards Applications)

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13 pages, 3403 KiB

Open AccessArticle

Morpho-Structural Investigations and Carbon Nanoclustering Effects in Cr-Al-C Intermetallic Alloys

by Alina Daniela Crisan and Ovidiu Crisan

Nanomaterials 2022, 12(18), 3225; https://doi.org/10.3390/nano12183225 - 16 Sep 2022

Cited by 3 | Viewed by 1418

Abstract

Intermetallic Cr-Al-C thin films from the 211 class of MAX phases were fabricated via ion beam deposition and structural investigations were undertaken to obtain information about morpho-structural effects propelled by carbon excess in the stoichiometry of the films. In order to promote the occurrence of the Cr₂AlC MAX phase, the stoichiometric thin films were subsequently annealed at two temperature values: 650 °C and 700 °C in UHV conditions for 30 min. The morpho-structural effects in both as-deposited and annealed films were monitored using scanning electron microscopy, X-ray diffraction, and Raman spectroscopy. XRD analysis showed that the as-deposited sample was almost completely crystallized in the hexagonal Cr₂AlC structure, with a remaining amorphous fraction of about 17%, most probably rich in carbon. Raman analysis allowed the identification of three spectral regions, two of them encompassing the Raman optical modes belonging to the Cr₂AlC 211 MAX phase, while the third one gave strong evidence of highly intense and large D- and G-bands of carbon. Structural parameters such as the crystal lattice parameters as well as the volume of the crystal unit cell were found to decrease upon annealing; this decrease is attributed to the grain growth. The average crystallite dimension was proven to increase after annealing, while the lattice micro-strain lowered to approximately 63% in the annealed thin film compared to the as-deposited one. Well-formed and intense Raman peaks attributed to D- and G-bands of carbon were also observed and, corroborated with the structural data, seemed to indicate an overall increased level of crystal ordering as well as potential carbon nanoclustering after thermal treatments with thin Cr₂AlC films. This observed phenomenon concords with previously documented reports on ab initio modelling of possible Cr₂AlC structures with carbon excess. Full article

(This article belongs to the Special Issue Current Research in Magnetic Nanomaterials: From Fundamentals towards Applications)

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15 pages, 3703 KiB

Open AccessArticle

Thermal Progress of Unsteady Separated Stagnation Point Flow with Magnetic Field and Heat Generation in Hybrid Ferrofluid

by Najiyah Safwa Khashi’ie, Iskandar Waini, Nurul Amira Zainal, Khairum Bin Hamzah, Abdul Rahman Mohd Kasim, Norihan Md Arifin and Ioan Pop

Nanomaterials 2022, 12(18), 3205; https://doi.org/10.3390/nano12183205 - 15 Sep 2022

Cited by 4 | Viewed by 1375

Abstract

This paper examines the unsteady separated stagnation point (USSP) flow and thermal progress of Fe₃O₄–CoFe₂O₄/H₂O on a moving plate subject to the heat generation and MHD effects. The model of the flow includes the boundary layer and energy equations. These equations are then simplified with the aid of similarity variables. The numerical results are generated by the bvp4c function and then presented in graphs and tables. The magnetic and acceleration (strength of the stagnation point flow) parameters are the contributing factors in the augmentation of the skin friction and heat transfer coefficients. However, the enhancement of heat generation parameter up to 10% shows a reduction trend in the thermal rate distribution of Fe₃O₄–CoFe₂O₄/H₂O. This finding reveals the effectiveness of heat absorption as compared to the heat generation in the thermal flow process. From the stability analysis, the first solution is the physical solution. The streamline for the first solution acts as a normal stagnation point flow, whereas the second solution splits into two regions, proving the occurrence of reverse flow. Full article

(This article belongs to the Special Issue Current Research in Magnetic Nanomaterials: From Fundamentals towards Applications)

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20 pages, 8323 KiB

Open AccessArticle

Raman, TEM, EELS, and Magnetic Studies of a Magnetically Reduced Graphene Oxide Nanohybrid following Exposure to Daphnia magna Biomarkers

by Juan A. Ramos-Guivar, Jacquelyne Y. Zarria-Romero, Yamerson Canchanya-Huaman, Jorge Andres Guerra, Noemi-Raquel Checca-Huaman, Isabel-Liz Castro-Merino and Edson C. Passamani

Nanomaterials 2022, 12(11), 1805; https://doi.org/10.3390/nano12111805 - 25 May 2022

Cited by 5 | Viewed by 1904

Abstract

A ternary nanocomposite made of nanomaghemite, nanoanatase, and graphene oxide has been successfully synthesized using an inorganic coprecipitation approach, and it has been systematically investigated by X-ray diffraction, transmission electron microscopy, and different spectrocopic techniques (electron energy loss, µ-Raman, and ⁵⁷Fe Mössbauer) after interaction with an effluent containing Daphnia magna individuals. Specifically, the influence of the nanocomposite over the Daphnia magna carapace, administered in two doses (0.5 mg mL⁻¹ and 1 mg mL⁻¹), has been characterized using µ-Raman spectroscopy before and after laser burning protocols, producing information about the physicochemical interaction with the biomarker. The thermal stability of the nanocomposite was found to be equal to 500 °C, where the nanoanatase and the nanomaghemite phases have respectively conserved their structural identities. The magnetic properties of the nanomaghemite have also been kept unchanged even after the high-temperature experiments and exposure to Daphnia magna. In particular, the size, texture, and structural and morphological properties of the ternary nanocomposite have not shown any significant physicochemical modifications after magnetic decantation recuperation. A significant result is that the graphene oxide reduction was kept even after the ecotoxicological assays. These sets of observations are based on the fact that while the UV-Vis spectrum has confirmed the graphene oxide reduction with a localized peak at 260 nm, the 300-K and 15-K ⁵⁷Fe Mössbauer spectra have only revealed the presence of stoichiometric maghemite, i.e., the two well-defined static magnetic sextets often found in the bulk ferrimagnetic counterpart phase. The Mössbauer results have also agreed with the trivalent-like valence state of Fe ions, as also suggested by electron energy loss spectroscopy data. Thus, the ternary nanocomposite does not substantially affect the Daphnia magna, and it can be easily recovered using an ordinary magnetic decantation protocol due to the ferrimagnetic-like character of the nanomaghemite phase. Consequently, it shows remarkable physicochemical properties for further reuse, such as cleaning by polluted effluents, at least where Daphnia magna species are present. Full article

(This article belongs to the Special Issue Current Research in Magnetic Nanomaterials: From Fundamentals towards Applications)

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17 pages, 4327 KiB

Open AccessArticle

Highly Sensitive Nanomagnetic Quantification of Extracellular Vesicles by Immunochromatographic Strips: A Tool for Liquid Biopsy

by Vera A. Bragina, Elena Khomyakova, Alexey V. Orlov, Sergey L. Znoyko, Elizaveta N. Mochalova, Liliia Paniushkina, Victoria O. Shender, Thalia Erbes, Evgeniy G. Evtushenko, Dmitry V. Bagrov, Victoria N. Lavrenova, Irina Nazarenko and Petr I. Nikitin

Nanomaterials 2022, 12(9), 1579; https://doi.org/10.3390/nano12091579 - 06 May 2022

Cited by 13 | Viewed by 2316

Abstract

Extracellular vesicles (EVs) are promising agents for liquid biopsy—a non-invasive approach for the diagnosis of cancer and evaluation of therapy response. However, EV potential is limited by the lack of sufficiently sensitive, time-, and cost-efficient methods for their registration. This research aimed at developing a highly sensitive and easy-to-use immunochromatographic tool based on magnetic nanoparticles for EV quantification. The tool is demonstrated by detection of EVs isolated from cell culture supernatants and various body fluids using characteristic biomarkers, CD9 and CD81, and a tumor-associated marker—epithelial cell adhesion molecules. The detection limit of 3.7 × 10⁵ EV/µL is one to two orders better than the most sensitive traditional lateral flow system and commercial ELISA kits. The detection specificity is ensured by an isotype control line on the test strip. The tool’s advantages are due to the spatial quantification of EV-bound magnetic nanolabels within the strip volume by an original electronic technique. The inexpensive tool, promising for liquid biopsy in daily clinical routines, can be extended to other relevant biomarkers. Full article

(This article belongs to the Special Issue Current Research in Magnetic Nanomaterials: From Fundamentals towards Applications)

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Review

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27 pages, 4908 KiB

Open AccessReview

Exchange Bias in Nanostructures: An Update

by Tomasz Blachowicz, Andrea Ehrmann and Martin Wortmann

Nanomaterials 2023, 13(17), 2418; https://doi.org/10.3390/nano13172418 - 25 Aug 2023

Cited by 3 | Viewed by 1270

Abstract

Exchange bias (EB) is a unidirectional anisotropy occurring in exchange-coupled ferromagnetic/antiferromagnetic systems, such as thin films, core–shell particles, or nanostructures. In addition to a horizontal shift of the hysteresis loop, defining the exchange bias, asymmetric loops and even vertical shifts can often be found. While the effect is used in hard disk read heads and several spintronics applications, its origin is still not fully understood. Especially in nanostructures with their additional shape anisotropies, interesting and often unexpected effects can occur. Here, we provide an overview of the most recent experimental findings and theoretical models of exchange bias in nanostructures from different materials. Full article

(This article belongs to the Special Issue Current Research in Magnetic Nanomaterials: From Fundamentals towards Applications)

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