Editorial

Jump to: Research

2 pages, 154 KiB

Open AccessEditorial

Magnetic Functional Materials: Synthesis, Characterization and Application: A New Open Special Issue in Materials

by

Haiou Wang

,

Yan Wang

and

Dexin Yang

Materials 2022, 15(9), 2999; https://doi.org/10.3390/ma15092999 - 20 Apr 2022

Viewed by 1304

Abstract

Magnetic Functional Materials: Synthesis, Characterization and Application is a new open Special Issue of Materials, which aims to publish original and review papers on new scientific and applied research, and make great contributions to the finding and understanding of magnetic functional materials [...] Read more.

Magnetic Functional Materials: Synthesis, Characterization and Application is a new open Special Issue of Materials, which aims to publish original and review papers on new scientific and applied research, and make great contributions to the finding and understanding of magnetic functional materials and related synthesis, fundamentals, characterization, and applications [...] Full article

(This article belongs to the Special Issue Magnetic Functional Materials: Synthesis, Characterization and Application)

Research

Jump to: Editorial

10 pages, 3727 KiB

Open AccessArticle

Comparisons of Dy Utilization Efficiency by DyH_x Grain Boundary Addition and Surface Diffusion Methods in Nd-Y-Fe-B Sintered Magnet

by

,

,

,

,

,

and

Materials 2022, 15(17), 5964; https://doi.org/10.3390/ma15175964 - 29 Aug 2022

Cited by 2 | Viewed by 911

Abstract

Using the heavy rare earth Dy element to improve coercivity is the most common solution for hindering the reduction in magnetic properties in the Nd–Fe–B magnet, and the effective utilization of Dy has become the focus of research in industrial society. In this [...] Read more.

Using the heavy rare earth Dy element to improve coercivity is the most common solution for hindering the reduction in magnetic properties in the Nd–Fe–B magnet, and the effective utilization of Dy has become the focus of research in industrial society. In this work, we investigated the influence of DyH_x addition and diffusion methods on the microstructure, magnetic performance, and thermal stability of the Nd–Y–Fe–B magnet with a Y-rich core structure. The coercivity of the DyH_x addition magnet increases from 9.45 kOe to 15.51 kOe when adding 1.6 wt.% DyH_x, while the DyH_x diffusion magnet increases to 15.15 kOe. According to the analysis of the microstructure and elemental distribution, both Dy-rich shells were basically formed due to the diffusion process of Dy atoms. The Dy-rich shell in the DyH_x addition magnet was similar with the original core–shell structure in the Nd–Y–Fe–B magnet. However, the distinct dual-shell structure consisting of a thinner Dy-rich shell and a Y-lean shell was constructed in the DyH_x diffused magnet, contributing to the superior coercivity increment and Dy utilization efficiency. Furthermore, the remanence of the DyH_x diffused magnet is up to 12.90 kG, which is better than that of the DyH_x addition magnet (12.59 kG), due to fewer Dy atoms entering the 2:14:1 matrix grain to cause the antiferromagnetic coupling with Fe atoms. Additionally, the thermal stability of the DyH_x diffusion magnet is also better than that of the DyH_x addition magnet, owing to the elevated coercivity at room temperature, which expands the application range of the Nd–Y–Fe–B magnet to a certain extent. Full article

(This article belongs to the Special Issue Magnetic Functional Materials: Synthesis, Characterization and Application)

► Show Figures

Figure 1

8 pages, 1959 KiB

Open AccessArticle

Transport Property and Spin–Orbit Torque in 2D Rashba Ferromagnetic Electron Gas

by

,

,

and

Materials 2022, 15(15), 5149; https://doi.org/10.3390/ma15155149 - 25 Jul 2022

Viewed by 711

Abstract

In this paper, we investigate the spin–orbit torque and transport property in a 2D Rashba ferromagnetic electron gas. The longitudinal conductivity can be divided into two parts: the first term is determined by the charge density and is independent of the spin degrees [...] Read more.

In this paper, we investigate the spin–orbit torque and transport property in a 2D Rashba ferromagnetic electron gas. The longitudinal conductivity can be divided into two parts: the first term is determined by the charge density and is independent of the spin degrees of freedom. The second term depends on the two bands that spin in the opposite directions, and it is directly proportional to spin–orbit torque regardless of the band structure and temperature. This is a general and underlying relation between the transport property and spin–orbit torque. Moreover, we show the impacts of the spin–orbit coupling constant and Fermi energy on transverse conductivity and spin–orbit torque, which is helpful for relevant experiments. Full article

(This article belongs to the Special Issue Magnetic Functional Materials: Synthesis, Characterization and Application)

► Show Figures

Figure 1

9 pages, 2457 KiB

Open AccessArticle

The Effect of Grain Size on the Diffusion Efficiency and Microstructure of Sintered Nd-Fe-B Magnets by Tb Grain Boundary Diffusion

by

,

,

,

,

,

,

and

Materials 2022, 15(14), 4987; https://doi.org/10.3390/ma15144987 - 18 Jul 2022

Cited by 3 | Viewed by 1030

Abstract

The grain boundary diffusion process (GBDP) of heavy rare earth Tb is an effective method to improve the coercivity of Nd-Fe-B magnets, and the matrix grain size has a crucial effect on the diffusion efficiency and depth of the Tb element. In this [...] Read more.

The grain boundary diffusion process (GBDP) of heavy rare earth Tb is an effective method to improve the coercivity of Nd-Fe-B magnets, and the matrix grain size has a crucial effect on the diffusion efficiency and depth of the Tb element. In this work, magnets with different grain sizes have been fabricated using powder metallurgy to investigate the effect of grain size on Tb diffusion efficiency and the microstructure of Nd-Fe-B-type magnets. After the Tb diffusion process, the coercivity increment of the magnet with 4.9 μm large grain is 8.60 kOe, which is much higher than that of the magnet with 3.0 μm small grain (~5.90 kOe), which clearly demonstrates that the coercivity increment decreases as the grain size decreases. Microstructure analysis suggested that grain refinement significantly increases the total surface area, resulting in narrowing and discontinuity of the grain boundary phase (GBP). Therefore, as the channel for diffusion, the narrowing and discontinuity of the GBP are unfavorable for diffusion, resulting in a decrease in diffusion efficiency. Full article

(This article belongs to the Special Issue Magnetic Functional Materials: Synthesis, Characterization and Application)

► Show Figures

Figure 1

9 pages, 749 KiB

Open AccessArticle

Tomonaga–Luttinger Spin Liquid and Kosterlitz–Thouless Transition in the Spin-1/2 Branched Chains: The Study of Topological Phase Transition

by

,

,

and

Materials 2022, 15(12), 4183; https://doi.org/10.3390/ma15124183 - 13 Jun 2022

Cited by 1 | Viewed by 1136

Abstract

In the present work, we provide a comprehensive numerical investigation of the magnetic properties and phase spectra of three types of spin-1/2 branched chains consisting of one, two and three side spins per unit block with intra-chain interaction and a uniform inter-chain interaction [...] Read more.

In the present work, we provide a comprehensive numerical investigation of the magnetic properties and phase spectra of three types of spin-1/2 branched chains consisting of one, two and three side spins per unit block with intra-chain interaction and a uniform inter-chain interaction in the presence of an external magnetic field. In a specific magnetic field interval, the low-temperature magnetization of these chains shows a step-like behavior with a pronounced plateau depending on the strength and the type of intra-chain interaction being ferromagnetic or antiferromagnetic. We demonstrate that when inter-chain interaction

J_{1}

is antiferromagnetic and intra-chain interaction

J_{2}

is ferromagnetic, the magnetization of the models manifests a smooth increase without a plateau, which is evidence of the existence of a Luttinger-like spin liquid phase before reaching its saturation value. On the other hand, when

J_{1}

is ferromagnetic and

J_{2}

is antiferromagnetic, the low-temperature magnetization of the chain with two branches shows an intermediate plateau at one-half of the saturation magnetization that breaks a quantum spin liquid phase into two regions. The magnetization of the chain with three branches exhibits two intermediate plateaus and two regions of a quantum spin liquid. We demonstrate that the chains with more than one side spin illustrate in their ground-state phase diagram a Kosterlitz–Thouless transition from a gapful phase to a gapless spin liquid phase. Full article

(This article belongs to the Special Issue Magnetic Functional Materials: Synthesis, Characterization and Application)

► Show Figures

Figure 1

10 pages, 4520 KiB

Open AccessEditor’s ChoiceArticle

Unraveling the Phase Stability and Physical Property of Modulated Martensite in Ni₂Mn_1.5In_0.5 Alloys by First-Principles Calculations

by

,

,

,

,

,

,

,

and

Materials 2022, 15(11), 4032; https://doi.org/10.3390/ma15114032 - 06 Jun 2022

Cited by 1 | Viewed by 1547

Abstract

Large magnetic field-induced strains can be achieved in modulated martensite for Ni-Mn-In alloys; however, the metastability of the modulated martensite imposes serious constraints on the ability of these alloys to serve as promising sensor and actuator materials. The phase stability, magnetic properties, and [...] Read more.

Large magnetic field-induced strains can be achieved in modulated martensite for Ni-Mn-In alloys; however, the metastability of the modulated martensite imposes serious constraints on the ability of these alloys to serve as promising sensor and actuator materials. The phase stability, magnetic properties, and electronic structure of the modulated martensite in the Ni₂Mn_1.5In_0.5 alloy are systematically investigated. Results show that the 6M and 5M martensites are metastable and will eventually transform to the NM martensite with the lowest total energy in the Ni₂Mn_1.5In_0.5 alloy. The physical properties of the incommensurate 7M modulated martensite (7M–IC) and nanotwinned 7M martensite (

7 M - {(5 \bar{2})}_{2}

) are also calculated. The austenite (A) and

7 M - {(5 \bar{2})}_{2}

phases are ferromagnetic (FM), whereas the 5M, 6M, and NM martensites are ferrimagnetic (FIM), and the FM coexists with the FIM state in the 7M–IC martensite. The calculated electronic structure demonstrates that the splitting of Jahn–Teller effect and the strong Ni–Mn bonding interaction lead to the enhancement of structural stability. Full article

(This article belongs to the Special Issue Magnetic Functional Materials: Synthesis, Characterization and Application)

► Show Figures

Figure 1

16 pages, 3108 KiB

Open AccessArticle

Microwave-Assisted Solvothermal Synthesis of Nanocrystallite-Derived Magnetite Spheres

by

,

,

,

,

,

and

Materials 2022, 15(11), 4008; https://doi.org/10.3390/ma15114008 - 05 Jun 2022

Cited by 2 | Viewed by 1531

Abstract

The synthesis of magnetic particles triggers the interest of many scientists due to their relevant properties and wide range of applications in the catalysis, nanomedicine, biosensing and magnetic separation fields. A fast synthesis of iron oxide magnetic particles using an eco-friendly and facile [...] Read more.

The synthesis of magnetic particles triggers the interest of many scientists due to their relevant properties and wide range of applications in the catalysis, nanomedicine, biosensing and magnetic separation fields. A fast synthesis of iron oxide magnetic particles using an eco-friendly and facile microwave-assisted solvothermal method is presented in this study. Submicron Fe₃O₄ spheres were prepared using FeCl₃ as an iron source, ethylene glycol as a solvent and reductor and sodium acetate as a precipitating and nucleating agent. The influence of the presence of polyethylene glycol as an additional reductor and heat absorbent was also evaluated. We reduce the synthesis time to 1 min by increasing the reaction temperature using the microwave-assisted solvothermal synthesis method under pressure or by adding PEG at lower temperatures. The obtained magnetite spheres are 200–300 nm in size and are composed of 10–30 nm sized crystallites. The synthesized particles were investigated using the XRD, TGA, pulsed-field magnetometry, Raman and FTIR methods. It was determined that adding PEG results in spheres with mixed magnetite and maghemite compositions, and the synthesis time increases the size of the crystallites. The presented results provide insights into the microwave-assisted solvothermal synthesis method and ensure a fast route to obtaining spherical magnetic particles composed of different sized nanocrystallites. Full article

(This article belongs to the Special Issue Magnetic Functional Materials: Synthesis, Characterization and Application)

► Show Figures

Graphical abstract

16 pages, 6620 KiB

Open AccessArticle

Sulfidized Nanoscale Zerovalent Iron Supported by Oyster Powder for Efficient Removal of Cr (VI): Characterization, Performance, and Mechanisms

by

,

,

and

Materials 2022, 15(11), 3898; https://doi.org/10.3390/ma15113898 - 30 May 2022

Cited by 4 | Viewed by 1248

Abstract

In this study, sulfidized nanoscale zerovalent iron (S-nZVI) supported by oyster shell (OS) powder (S-nZVI@OS) was synthesized by controlling the initial S/Fe ratios (0.1–0.5) to explore the potential synergistic effects during the adsorption and reduction of Cr (VI). X-ray diffraction (XRD), transmission electron [...] Read more.

In this study, sulfidized nanoscale zerovalent iron (S-nZVI) supported by oyster shell (OS) powder (S-nZVI@OS) was synthesized by controlling the initial S/Fe ratios (0.1–0.5) to explore the potential synergistic effects during the adsorption and reduction of Cr (VI). X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray photoelectron spectroscopy (XPS) analyses showed that Fe (0) and FeS were well dispersed on the OS surface. Furthermore, the stability of S-nZVI@OS composite was higher than that of nZVI, which was proved by the material ageing experiment. The effects of different S/Fe molar ratios, time, temperature, the initial concentration of Cr (VI), and initial pH on the removal efficiency were also studied. The results indicated that with the increase of the S/Fe molar ratio, the removal capacity of Cr (VI) first increased rapidly and then decreased slowly. Batch experiments showed that an optimal S/Fe molar ratio of 0.2 offered a Cr (VI) removal capacity of about 164.7 mg/g at pH 3.5. The introduction of S can not only promote Cr (VI) reduction but also combine with Cr (III) by forming precipitate on S-nZVI@OS mainly as Cr_xFe_(1−x) OOH and Cr₂S₃. The adsorption thermodynamics and kinetics demonstrated that the Langmuir model and pseudo-second-order kinetics model can describe the adsorption isotherms and kinetics. These results suggest that S-nZVI@OS is an effective and safe material for removing Cr (VI) from aqueous solutions. Full article

(This article belongs to the Special Issue Magnetic Functional Materials: Synthesis, Characterization and Application)

► Show Figures

Graphical abstract

14 pages, 6680 KiB

Open AccessArticle

Effect of Polyimide-Phosphating Double Coating and Annealing on the Magnetic Properties of Fe-Si-Cr SMCs

by

,

,

,

and

Materials 2022, 15(9), 3350; https://doi.org/10.3390/ma15093350 - 07 May 2022

Cited by 8 | Viewed by 1286

Abstract

Fe-Si-Cr soft magnetic powder cores (SMCs), with high electrical resistivity, magnetic permeability, saturation magnetic induction, and good corrosion resistance, are widely applied to inductors, filters, choke coils, etc. However, with the development of electronic technology with high frequency and high power density, the [...] Read more.

Fe-Si-Cr soft magnetic powder cores (SMCs), with high electrical resistivity, magnetic permeability, saturation magnetic induction, and good corrosion resistance, are widely applied to inductors, filters, choke coils, etc. However, with the development of electronic technology with high frequency and high power density, the relative decline in the magnetic properties limits the high-frequency application of SMCs. In this paper, the phosphating process and polyimide (PI) insulation coating is applied to Fe-Si-Cr SMCs to reduce the core loss, including hysteresis loss and eddy current loss. The microstructure and composition of Fe-Si-Cr powders were analyzed by SEM, XRD, and Fourier-transform infrared spectra, respectively. The structural characteristics of the Fe-Si-Cr @ phosphate layer @ PI layer core–shell double coating were studied, and the best process parameters were determined through experiments. For SMCs with 0.4 wt% content of PI, the relative permeability is greater than 68%, and the core loss is the lowest, 7086 mW/cm³; annealed at 500 °C, the relative permeability is greater than 57%, and the core loss is the lowest, 6222 mW/cm³. A 0.4 wt% content of PI, annealed at 500 °C, exhibits the ideal magnetic properties: μ_e = 47 H/m, P = 6222 mW/cm³. Full article

(This article belongs to the Special Issue Magnetic Functional Materials: Synthesis, Characterization and Application)

► Show Figures

Figure 1

11 pages, 2873 KiB

Open AccessArticle

A Study on the Static Magnetic and Electromagnetic Properties of Silica-Coated Carbonyl Iron Powder after Heat Treatment for Improving Thermal Stability

by

,

,

,

,

and

Materials 2022, 15(7), 2499; https://doi.org/10.3390/ma15072499 - 28 Mar 2022

Cited by 4 | Viewed by 1389

Abstract

In order to study the thermal stability of coated carbonyl iron powder (CIP) and its influence on magnetic properties, carbonyl iron powder was coated with a silica layer and then annealed in an air atmosphere at elevated temperatures. Transmission electron microscopy (TEM) analysis [...] Read more.

In order to study the thermal stability of coated carbonyl iron powder (CIP) and its influence on magnetic properties, carbonyl iron powder was coated with a silica layer and then annealed in an air atmosphere at elevated temperatures. Transmission electron microscopy (TEM) analysis and Fourier transform infrared spectroscopy confirmed the existence of a silicon dioxide layer with a thickness of approximately 80~100 nm. Compared with uncoated CIP, the silicon-coated CIP still maintained a higher absorption performance after annealing, and the calculated impedance matching value Z only slightly decreased. It is worth noting that when the annealing temperature reached 300 °C, coercivity (H_c) increased, and the real and imaginary parts of the permeability decreased, which means that the silicon dioxide layer began to lose its effectiveness. On the contrary, the significant decrease in microwave absorption ability and impedance matching value Z of uncoated CIP after annealing were mainly because the newly formed oxide on the interface became the active polarization center, leading to an abnormal increase in permittivity. In terms of the incremental mass ratio after annealing, 2% was a tipping point for permeability reduction. Full article

(This article belongs to the Special Issue Magnetic Functional Materials: Synthesis, Characterization and Application)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Special Issue "Magnetic Functional Materials: Synthesis, Characterization and Application"

Share This Special Issue

Special Issue Editors

Special Issue Information

Keywords

Published Papers (10 papers)

Editorial

Research

Further Information

Guidelines

MDPI Initiatives

Follow MDPI