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A special issue of Materials (ISSN 1996-1944). This special issue belongs to the section "Materials Physics".

Deadline for manuscript submissions: closed (30 November 2020) | Viewed by 38272

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Prof. Dr. Michael R. Koblischka

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Superconducting Materials Laboratory, Department of Materials Science and Engineering, Shibaura Institute of Technology 3‐7‐5 Toyosu, Koto‐ku, Tokyo, Japan
Interests: magnetic materials; ceramics (ferrites and manganites); magnetic imaging; magnetic characterization
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Prof. Dr. Anjela Koblischka-Veneva

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Collection Editor

Department of Materials Science and Engineering, Shibaura Institute of Technology, Toyosu, Koto-ku, Tokyo 135-8548, Japan
Interests: superconducting and magnetic materials (ferrites and manganates); ceramics; bulk high Tc superconductors; material characterization; microstructures; texture analysis; electron microscopy; electron backscatter diffraction; orientation imaging; nanostructuring; biomaterials
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The fabrication of magnetic materials is a long-standing topic, and magnetic materials are employed nowadays in a variety of applications including magnetic recording, magnetic sensor technology, magnetic levitation, magnetic cooling, spintronics, and many more. However, the modern challenges of ecology, ressource-friendliness, and environmental issues place more stringent demands for the research on magnetic materials. Many efforts have been invested in producing environmentaly friendly materials, to consume less energy in use, to be more cost effective, to reduce the weight of devices, and to consume less resources like costly rare-earth materials or the rare Lithium. Moreover, issues of material recycling have to be considered. Therefore, this Special Issue of Materials is aimed at providing a collection of papers focusing on modern material preparation technologies, new material structuring approaches, new shapes and designs of materials and new routes to optimize the material parameters in view of the application demands.

The topics of interest include, but are not limited to:

Fabrication of ferromagnetic materials; hard and soft types (powders, bulks, thin-films, composite materials);
Search of rare-earth free magnetic materials;
Alternative ways to generate high magnetic fields including superconducting trapped-field magnets;
Processing technologies: Deposition of films, structuring, ink jet-printing, 3D-printing, new shapes of materials (nanowires, porous materials, composites);
Investigation of microstructure;
Magnetic imaging (MRI, magnetic force microscopy, magneto-optics);
Tuning the magnetic properties to higher efficiency;
Materials issues for spintronics;
Optimizing the properties magnetic materials for given applications;
New emerging applications of magnetic materials

Prof. Dr. Michael R. Koblischka
Prof. Dr. Anjela Koblischka-Veneva
Collection Editors

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Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Materials is an international peer-reviewed open access semimonthly journal published by MDPI.

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Keywords

ferromagnetism
hard and soft magnetic materials
ferrites, rare-earth elements
spintronics, microstructure, magnetic imaging, preparation

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Published Papers (12 papers)

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Research

14 pages, 3594 KiB

Open AccessArticle

Structural Quality and Magnetotransport Properties of Epitaxial Layers of the (Ga,Mn)(Bi,As) Dilute Magnetic Semiconductor

by Tomasz Andrearczyk, Khrystyna Levchenko, Janusz Sadowski, Jaroslaw Z. Domagala, Anna Kaleta, Piotr Dłużewski, Jerzy Wróbel, Tadeusz Figielski and Tadeusz Wosinski

Materials 2020, 13(23), 5507; https://doi.org/10.3390/ma13235507 - 3 Dec 2020

Cited by 8 | Viewed by 3032

Abstract

Structural analysis of epitaxial layers of the (Ga,Mn)(Bi,As) quaternary dilute magnetic semiconductor (DMS), together with investigations of their magnetotransport properties, has been thoroughly performed. The obtained results are compared with those for the reference (Ga,Mn)As layers, grown under similar conditions, with the aim to reveal an impact of Bi incorporation on the properties of this DMS material. Incorporation of Bi into GaAs strongly enhances the spin-orbit coupling strength in this semiconductor, and the same has been expected for the (Ga,Mn)(Bi,As) alloy. In turn, importantly for specific spintronic applications, strong spin-orbit coupling in ferromagnetic systems opens a possibility of directly controlling the direction of magnetization by the electric current. Our investigations, performed with high-resolution X-ray diffractometry and transmission electron microscopy, demonstrate that the (Ga,Mn)(Bi,As) layers of high structural quality and smooth interfaces can be grown by means of the low-temperature molecular-beam epitaxy method, despite a large difference between the sizes of Bi and As atoms. Depending on the applied buffer layer, the DMS layers can be grown under either compressive or tensile misfit strain, which influences their magnetic properties. It is shown that even small 1% Bi content in the layers strongly affects their magnetoelectric properties, such as the coercive field and anisotropic magnetoresistance. Full article

(This article belongs to the Special Issue Magnetic Materials and Applications)

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12 pages, 2558 KiB

Open AccessArticle

The Effect of Particle Shell on Cooling Rates in Oil-in-Oil Magnetic Pickering Emulsions

by Rafał Bielas and Arkadiusz Józefczak

Materials 2020, 13(21), 4783; https://doi.org/10.3390/ma13214783 - 26 Oct 2020

Cited by 10 | Viewed by 2498

Abstract

Pickering emulsions (particle-stabilized emulsions) are usually considered because of their unique properties compared to surfactant-stabilized emulsions including better stability against emulsion aging. However, the interesting feature of particle-stabilized emulsions could be revealed during their magnetic heating. When magnetic particles constitute a shell around droplets and the sample is placed in an alternating magnetic field, a temperature increase appears due to energy dissipation from magnetic relaxation and hysteresis within magnetic particles. We hypothesize that the solidity of the magnetic particle shell around droplets can influence the process of heat transfer from inside the droplet to the surrounding medium. In this way, particle-stabilized emulsions can be considered as materials with changeable heat transfer. We investigated macroscopically heating and cooling of oil-in-oil magnetic Pickering emulsions with merely packed particle layers and these with a stable particle shell. The change in stability of the shell was obtained here by using the coalescence of droplets under the electric field. The results from calorimetric measurements show that the presence of a stable particle shell caused a slower temperature decrease in samples, especially for lower intensities of the magnetic field. The retarded heat transfer from magnetic Pickering droplets can be utilized in further potential applications where delayed heat transfer is desirable. Full article

(This article belongs to the Special Issue Magnetic Materials and Applications)

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19 pages, 5315 KiB

Open AccessArticle

Antiferromagnetic Ordering and Transport Anomalies in Single-Crystalline CeAgAs₂

by Maria Szlawska, Daniel Gnida, Piotr Ruszała, Maciej J. Winiarski, Małgorzata Samsel-Czekała, Marcus Schmidt, Yuri Grin and Dariusz Kaczorowski

Materials 2020, 13(17), 3865; https://doi.org/10.3390/ma13173865 - 1 Sep 2020

Cited by 5 | Viewed by 3117

Abstract

Single crystals of the ternary cerium arsenide CeAgAs₂ were grown by chemical vapor transport. They were studied by means of x-ray diffraction, magnetization, heat capacity and electrical transport measurements. The experimental research was supplemented with electronic band structure calculations. The compound was confirmed to order antiferromagnetically at the Néel temperature of 4.9 K and to undergo metamagnetic transition in a field of 0.5 T at 1.72 K. The electrical resistivity shows distinct increase at low temperatures, which origin is discussed in terms of pseudo-gap formation in the density of states at the Fermi level and quantum corrections to the resistivity in the presence of atom disorder due to crystal structure imperfections. Full article

(This article belongs to the Special Issue Magnetic Materials and Applications)

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17 pages, 2334 KiB

Open AccessArticle

Limitations in the Grain Boundary Processing of the Recycled HDDR Nd-Fe-B System

by Awais Ikram, Muhammad Awais, Richard Sheridan, Allan Walton, Spomenka Kobe, Franci Pušavec and Kristina Žužek Rožman

Materials 2020, 13(16), 3528; https://doi.org/10.3390/ma13163528 - 10 Aug 2020

Cited by 3 | Viewed by 2612

Abstract

Fully dense spark plasma sintered recycled and fresh HDDR Nd-Fe-B nanocrystalline bulk magnets were processed by surface grain boundary diffusion (GBD) treatment to further augment the coercivity and investigate the underlying diffusion mechanism. The fully dense SPS processed HDDR based magnets were placed in a crucible with varying the eutectic alloys Pr₆₈Cu₃₂ and Dy₇₀Cu₃₀ at 2–20 wt. % as direct diffusion source above the ternary transition temperature for GBD processing followed by secondary annealing. The changes in mass gain was analyzed and weighted against the magnetic properties. For the recycled magnet, the coercivity (H_Ci) values obtained after optimal GBDP yielded ~60% higher than the starting recycled HDDR powder and 17.5% higher than the SPS-ed processed magnets. The fresh MF-15P HDDR Nd-Fe-B based magnets gained 25–36% higher coercivities with Pr-Cu GBDP. The FEG-SEM investigation provided insight on the diffusion depth and EDXS analysis indicated the changes in matrix and intergranular phase composition within the diffusion zone. The mechanism of surface to grain boundary diffusion and the limitations to thorough grain boundary diffusion in the HDDR Nd-Fe-B based bulk magnets were detailed in this study. Full article

(This article belongs to the Special Issue Magnetic Materials and Applications)

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14 pages, 4514 KiB

Open AccessArticle

Characterization of Damage Evolution on Hot Flat Rolled Mild Steel Sheets by Means of Micromagnetic Parameters and Fatigue Strength Determination

by Mirko Teschke, Julian Rozo Vasquez, Lukas Lücker and Frank Walther

Materials 2020, 13(11), 2486; https://doi.org/10.3390/ma13112486 - 29 May 2020

Cited by 12 | Viewed by 3032

Abstract

In continuous casting processes, inevitable voids (damage) are generated inside the material. The subsequent forming process of hot flat rolling offers the potential of healing these defects by closing the voids and bonding the internal surfaces. In this paper, different forming conditions from hot flat rolling process were characterized with micromagnetic measurement techniques and the influence of the damage evolution on the fatigue behavior was investigated. To characterize the reduction of voids through hot flat rolling processes, nondestructive testing techniques are required. Therefore, micromagnetic measurements such as Barkhausen noise, incremental permeability, and harmonic analysis were carried out, correlated with the number of voids, and compared with each other. The influence of damage evolution of different forming conditions on the fatigue behavior was characterized based on instrumented constant amplitude and multiple amplitude (load increase) tests. A significant increase in fatigue strength due to the hot flat rolling process, which leads to a reduction in the number of voids, was observed. In addition, the fracture surfaces of the specimens were analyzed in the scanning electron microscope. Full article

(This article belongs to the Special Issue Magnetic Materials and Applications)

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16 pages, 25435 KiB

Open AccessArticle

Structural, Magnetic and Microwave Characterization of Polycrystalline Z-Type Sr₃Co₂Fe₂₄O₄₁ Hexaferrite

by Svetoslav Kolev, Petya Peneva, Kiril Krezhov, Tanya Malakova, Chavdar Ghelev, Tatyana Koutzarova, Daniela Kovacheva, Benedicte Vertruyen, Raphael Closset, Lan Maria Tran and Andrzej Zaleski

Materials 2020, 13(10), 2355; https://doi.org/10.3390/ma13102355 - 20 May 2020

Cited by 8 | Viewed by 3487

Abstract

We report results on the structural and microwave properties and magnetic phase transitions in polycrystalline Sr₃Co₂Fe₂₄O₄₁ hexaferrite synthesized by sol-gel auto-combustion and acting as a filler in a composite microwave absorbing material. The zero-field-cooled (ZFC) and field-cooled (FC) magnetization curves revealed a change in the magnetization behavior at 293 K. The reflection losses in the 1–20 GHz range of the Sr₃Co₂Fe₂₄O₄₁ powder dispersed homogeneously in a polymer matrix of silicon rubber were investigated in both the absence and presence of a magnetic field. In the latter case, a dramatic rise in the attenuation was observed. The microwave reflection losses reached the maximum value of 32.63 dB at 17.29 GHz in the Ku-band. The sensitivity of the microwave properties of the composite material to the external magnetic field was manifested by the appearance of new reflection losses maxima. At a fixed thickness t_m of the composite, the attenuation peak frequency can be adjusted to a certain value either by changing the filling density or by applying an external magnetic field. Full article

(This article belongs to the Special Issue Magnetic Materials and Applications)

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17 pages, 12746 KiB

Open AccessArticle

Correlation between Magnetic Properties and Chemical Composition of Non-Oriented Electrical Steels Cut through Different Technologies

by Gheorghe Paltanea, Veronica Manescu (Paltanea), Radu Stefanoiu, Iosif Vasile Nemoianu and Horia Gavrila

Materials 2020, 13(6), 1455; https://doi.org/10.3390/ma13061455 - 23 Mar 2020

Cited by 14 | Viewed by 4469

Abstract

Due to worldwide regulations on electric motor manufacturing, the energy efficiency of these devices has to be constantly improved. A solution may reside in the fact that high quality materials and adequate cutting technologies should be carefully chosen. The magnetic properties of non-oriented electrical steels are affected by the cutting methods, through induced plastic, and thermal stresses. There is also an important correlation between chemical composition and different magnetic properties. In this paper, we analyze different industrial grades of non-oriented electrical steels, used in electrical machines’ core manufacturing as M800-65A, M800-50A, M400-65A, M400-50A, M300-35A, and NO20. The influence of the cutting methods on the normal magnetization curve, total energy loss and its components, and relative magnetic permeability is investigated in alternating currents using a laboratory single sheet tester. The chemical composition and grain size influence are analyzed and correlated with the magnetic properties. Special attention is devoted to the influence of the increased cutting perimeter on the energy losses and to the way it relates to each chemical alloy constituent. The final decision in what concerns the choice of the proper magnetic material and the specific cutting technology for the motor magnetic cores is imposed by the desired efficiency class and the specific industrial applications. Full article

(This article belongs to the Special Issue Magnetic Materials and Applications)

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6 pages, 3900 KiB

Open AccessArticle

Multiple Transitions in Permalloy Half-Ring Wires with Finite-Size Effect

by Cheng-Yi Wu and Shiow-Kang Yen

Materials 2020, 13(6), 1384; https://doi.org/10.3390/ma13061384 - 19 Mar 2020

Viewed by 1860

Abstract

Six permalloy (Py) half-rings with finite-size from 120 nm to 360 nm were connected in series on five corners. The magnetization reversal processes were investigated by the measurement of anisotropic magnetoresistance (AMR). The number of switching jumps in the AMR loops, from zero to five, varied with the longitudinal applied field. These discrete jumps resulted from domain wall (DW) nucleating and depinning on the corners. The larger external field had a fewer number of jumps in the magnetoresistance (MR) curve. This reproducible and particular response of the domain wall device in the half-ring wires pattern might be one of the new promising magnetoelectronic devices. Full article

(This article belongs to the Special Issue Magnetic Materials and Applications)

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14 pages, 6315 KiB

Open AccessArticle

The AC Soft Magnetic Properties of FeCoNi_xCuAl (1.0 ≤ x ≤ 1.75) High-Entropy Alloys

by Zhongyuan Wu, Chenxu Wang, Yin Zhang, Xiaomeng Feng, Yong Gu, Zhong Li, Huisheng Jiao, Xiaohua Tan and Hui Xu

Materials 2019, 12(24), 4222; https://doi.org/10.3390/ma12244222 - 16 Dec 2019

Cited by 16 | Viewed by 3599

Abstract

High-entropy alloys (HEAs) with soft magnetic properties are one of the new candidate soft magnetic materials which are usually used under an alternating current (AC) magnetic field. In this work, the AC soft magnetic properties are investigated for FeCoNi_xCuAl (1.0 ≤ x ≤ 1.75) HEAs. The X-ray diffraction (XRD) and scanning electron microscope (SEM) show that the alloy consists of two phases, namely a face-centred cubic (FCC) phase and a body-centred cubic (BCC) phase. With increasing Ni content, the FCC phase content increased. Further research shows that the AC soft magnetic properties of these alloys are closely related to their phase constitution. Increasing the FCC phase content contributes to a decrease in the values of AC remanence (AC B_r), AC coercivity (AC H_c) and AC total loss (P_s), while it is harmful to the AC maximum magnetic flux density (AC B_m). P_s can be divided into two parts: AC hysteresis loss (P_h) and eddy current loss (P_e). With increasing frequency f, the ratio of P_h/P_s decreases for all samples. When f ≤ 150 Hz, P_h/P_s > 70%, which means that P_h mainly contributes to P_s. When f ≥ 800 Hz, P_h/P_s < 40% (except for the x = 1.0 sample), which means that P_e mainly contributes to P_s. At the same frequency, the ratio of P_h/P_s decreases gradually with increasing FCC phase content. The values of P_e and P_h are mainly related to the electrical resistivity (ρ) and the AC H_c, respectively. This provides a direction to reduce P_s. Full article

(This article belongs to the Special Issue Magnetic Materials and Applications)

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11 pages, 3388 KiB

Open AccessArticle

Assessment of Tendon Prestressing after Long-Term Service via the Barkhausen Noise Technique

by Miroslav Neslušan, František Bahleda, Martin Moravčík, Katarína Zgútová and Filip Pastorek

Materials 2019, 12(20), 3450; https://doi.org/10.3390/ma12203450 - 22 Oct 2019

Cited by 13 | Viewed by 2631

Abstract

This paper deals with the assessment of a real prestressed tendon by the use of Barkhausen noise emission. The tendon was obtained from a real highway bridge after 33 years in service. Barkhausen noise is studied as a function of the stress state, and the Barkhausen noise signals received directly from the tendon on the real bridge are compared with the Barkhausen noise signals received from the tendon during loading in the laboratory. Assessment of the prestressing is based on the analysis of the effective value of the Barkhausen noise signal as well as the position in which the Barkhausen noise envelopes attain a maximum. Full article

(This article belongs to the Special Issue Magnetic Materials and Applications)

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9 pages, 2519 KiB

Open AccessArticle

Nonlinear Magnetoelectric Response of Fe_73.5Cu₁Nb₃Si_13.5B₉/Piezofiber Composite for a Pulsed Magnetic Field Sensor

by Caijiang Lu, Hai Zhou, Aichao Yang, Zhengyu Ou, Feihu Yu and Hongli Gao

Materials 2019, 12(18), 2866; https://doi.org/10.3390/ma12182866 - 5 Sep 2019

Cited by 11 | Viewed by 2770

Abstract

In this paper, we report the nonlinear magnetoelectric response in a homogenous magnetostrictive/piezoelectric laminate material. The proposed magnetoelectric stack Fe_73.5Cu₁Nb₃Si_13.5B₉/piezofiber is made up of high-permeability magnetostrictive Fe_73.5Cu₁Nb₃Si_13.5B₉ foils and a piezoelectric Pb(Zr, Ti)O₃ fiber composite. The time dependence of magnetoelectric interactions in the Fe_73.5Cu₁Nb₃Si_13.5B₉/piezofiber structure driven by pulsed magnetic field was investigated in detail. The experimental results show that the magnetoelectric effect is strongly dependent on the external bias magnetic and pulsed magnetic field parameters. To detect the amplitude of a pulsed magnetic field, the output sensitivity reaches 17 mV/Oe, which is excited by a 100 μs width field. In addition, to measure the pulsed width, the output sensitivity reaches 5.4 mV/μs in the range of 0–300 μs. The results show that the proposed Fe_73.5Cu₁Nb₃Si_13.5B₉/piezofiber sensor is ideally suited for pulsed magnetic field measurement. Full article

(This article belongs to the Special Issue Magnetic Materials and Applications)

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7 pages, 7527 KiB

Open AccessArticle

Marked Enhancement of Roll-Off Frequency in FeCoN Synthetic Antiferromagnetic Films Deposited by Oblique Incidence

by Luran Zhang, Dandan Gao, Huan Liu, Jiyang Xie and Wanbiao Hu

Materials 2019, 12(14), 2328; https://doi.org/10.3390/ma12142328 - 22 Jul 2019

Cited by 3 | Viewed by 2852

Abstract

A series of FeCoN films were successfully deposited on glass substrates in a magnetron sputtering system. Using oblique incidence method and FeCoN/Ru/FeCoN synthetic antiferromagnetic (SAF) structure, two additional anisotropies energy were introduced: oblique incidence anisotropy and exchange anisotropy energy, which marked enhancement of the effective magnetic anisotropy (Hk). The increment of Hk results in a significant improvement in the roll-off frequency of these films. The roll-off frequency of FeCoN/Ru/FeCoN films with SAF structure can reach up to 8.6 GHz. A feasible approach to conveniently controlling Hk of soft magnetic thin films by using oblique deposition and SAF structure can further improve their properties for the potential applications in the high frequency region. Full article

(This article belongs to the Special Issue Magnetic Materials and Applications)

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