Anisotropic Magnetic Properties Research Articles

Direct and inverse magnetocaloric effects in magnetostrictive GdMn2Ge2 with field-induced metamagnetic transition

Heavy rare-earth-based ternary intermetallic compounds with the formula RT2X2 have drawn great interest because of their multiple magnetic transitions and various magnetic structures. Here, anisotropic magnetic behaviors, magnetocaloric effects (MCEs), and magnetostriction effects in single-crystalline GdMn2Ge2 are studied in two different directions. Experiments show a magnetic transition characterized by a sudden decrease in magnetization for μ0H//a and a sharp increase for μ0H//c at Tt. The transition is driven by lower temperatures for μ0H//a, contrasting that for μ0H//c with an increase in the magnetic field. An inverse MCE is observed for μ0H//a with a maximum magnetic entropy change (−ΔSMmax) of −7.4 J kg−1 K−1 (μ0ΔH = 6 T), while a direct MCE is obtained for μ0H//c with an −ΔSMmax of 8.0 J kg−1 K−1 under the same magnetic field change. Moreover, a remarkable field-induced metamagnetic transition and a magnetostriction effect are observed simultaneously at Tt, indicating strong magneto-lattice coupling. The T-μ0H phase diagrams are constructed based on the magnetic properties. The coexistence of direct and inverse MCEs is discussed and is due to the spin-flop of Mn and anisotropic magnetic properties under magnetic fields in different directions.

Peculiarities of spin–orbit interaction systematically measured in FeCoB nanomagnets

This study introduces a method to measure the strength of spin–orbit interaction (SO) in a nanomagnet, investigating fundamental phenomena governing magnetic anisotropy. The method explores the fundamental property of SO in its linear proportionality to the external magnetic field, a relationship validated through experimental observation. Systematic study of SO in FeCoB nanomagnets reveals distinct SO behaviors in bulk and at an interface, substantial disparities in single- and multi-layer nanomagnets, intriguing periodic oscillations in SO strength, and the systematic relationship between SO strength, demagnetization field, and magnetic anisotropy based on surface imperfections. These findings provide crucial insights into diverse SO interaction behaviors, crucial for understanding and optimizing magnetic anisotropy and nanomagnet properties.

Effects of inserted ultrathin Pt buffer on perpendicular magnetic properties of Ta/TbFeCo/Ta layered structures

We investigated effects of inserted ultrathin Pt buffer on the perpendicular magnetic properties of Ta/TbFeCo/Ta layered structures. For Tb-rich TbFeCo films buffered with Ta and Ta/Pt a compensation thickness is observed at ∼ 6 nm, where the net saturation magnetization vanishes. The perpendicular magnetic anisotropy properties of two structures are found to be governed by a competition of a perpendicular bulk anisotropy and an in-plane interface anisotropy. Compared with Ta-buffered TbFeCo films, the counterparts with insertion of Pt buffer exhibits a larger negative interface anisotropy. A large variation of saturation magnetization and perpendicular magnetic anisotropy with increasing inserted thickness of Pt buffer is observed in the Ta/Pt/TbFeCo/Ta structure. This can be ascribed to the interface-driven variation of exchange interaction between Tb and FeCo at the interface, confirmed by thermomagnetic measurements. A clear correlation between the interface-driven variation of exchange interaction and perpendicular magnetic properties of the TbFeCo films is identified. Our results show the interface plays an important role in the perpendicular magnetic properties of TbFeCo films, which is critical for the application in spintronic devices.

The Success of Fabrication of Pure SmFe2 Phase Film with Outstanding Perpendicular Magnetic Anisotropy.

This study used DC magnetron sputtering technology to fabricate Sm-Fe films and systematically investigated the phase transition behavior of Sm-Fe films with different Fe ratios. It was found that at higher Fe content, the films consisted of Sm2Fe17 or SmFe7 phases; as Fe content decreased, the films were mainly composed of SmFe3 or SmFe2 phases; at higher Sm content, the films primarily consisted of Sm phase. Sm is prone to volatilization at high temperatures, so Ta was used as a capping layer to effectively suppress Sm volatilization, successfully synthesizing pure SmFe2 phase films at a nearly 1:2 ratio. The magnetic properties and magnetostrictive behavior of the SmFe2 films were investigated, revealing that pure-phase SmFe2 films exhibit good perpendicular magnetic anisotropy and magnetostriction properties. The larger stress along the perpendicular-to-film direction, resulting from the absence of substrate-induced constraints, contributes to the excellent perpendicular magnetic anisotropy of the films. This study successfully synthesized pure-phase SmFe2 films and discovered a new method for fabricating perpendicularly anisotropic films. The research findings are of great significance for the efficient synthesis of desired films with high phase formation temperatures containing volatile elements.

Investigation on the physical origins of laser effects on anisotropic magnetic properties of GO electrical steels by means of thermal annealing

Both conventional laser surface treatments (irradiation or scribing) and recently developed ablation process performed with UltraShort Pulse Lasers (USPL) can improve magnetic properties of Grain-Oriented Electrical Steels (GOES) along their Rolling Direction (RD). While pushing the study of laser treatments further, interesting power loss reductions could also be obtained along the Transverse Direction (TD) (or other directions) of GOES using the ablation process with adapted laser patterns. To better understand the physical origins of loss reductions obtained with the USPL ablation process, the effects of a thermal annealing on GOES laser treated with various patterns are investigated. Results differ depending on the excitation direction and in connection with the applied laser treatment and pattern, which provides an original insight into the origins of the modifications of magnetic properties by laser.

Effect of Annealing Temperature and Time on the Magnetic Properties and Magnetic Anisotropy of a Temper-Rolled, Semi-processed Non-oriented Electrical Steel

The effect of final annealing temperature and time on the core loss, magnetic permeability, and magnetic anisotropy of a temper-rolled, semi-processed 0.5 wt.% Si non-oriented electrical steel was investigated. The magnetic properties of the steel sheets at 50–400 Hz and 0.5–1.50 T were measured by the Epstein frame method on strips cut along both the rolling (RD) and transverse directions (TD). Optimal magnetic properties were obtained when the annealing temperature was at 800–825°C, and the annealing time was 2–4 h. Relatively large magnetic anisotropy between the RD and TD was observed in samples after recrystallization (~ 10% in core loss and ~ 70% in relative permeability), while deformed and non-recrystallized samples showed small anisotropy in magnetic properties. Regardless of the processing state of the steel, i.e., temper-rolled, recovered, or recrystallized, the core loss followed quadratic polynomial functions with respect to both the frequency and magnetic flux density, while the relative magnetic permeability followed cubic polynomial functions with respect to both the frequency and magnetic flux density. The microstructure and texture of selected samples were characterized by electron backscatter diffraction, which revealed the correlations between the magnetic properties of the steel and the microstructure and texture.

Features of Anisotropic Drug Delivery Systems.

Natural materials are anisotropic. Delivery systems occurring in nature, such as viruses, blood cells, pollen, and many others, do have anisotropy, while delivery systems made artificially are mostly isotropic. There is apparent complexity in engineering anisotropic particles or capsules with micron and submicron sizes. Nevertheless, some promising examples of how to fabricate particles with anisotropic shapes or having anisotropic chemical and/or physical properties are developed. Anisotropy of particles, once they face biological systems, influences their behavior. Internalization by the cells, flow in the bloodstream, biodistribution over organs and tissues, directed release, and toxicity of particles regardless of the same chemistry are all reported to be factors of anisotropy of delivery systems. Here, the current methods are reviewed to introduce anisotropy to particles or capsules, including loading with various therapeutic cargo, variable physical properties primarily by anisotropic magnetic properties, controlling directional motion, and making Janus particles. The advantages of combining different anisotropy in one entity for delivery and common problems and limitations for fabrication are under discussion.

LnDOTA puppeteering: removing the water molecule and imposing tetragonal symmetry.

Complexes of lanthanide(iii) ions (Ln) with tetraazacyclododecane-N,N',N'',N'''-tetraacetate (DOTA) are a benchmark in the field of magnetism due to their well-investigated and sometimes surprising features. Ab initio calculations suggest that the ninth ligand, an axial water molecule, is key in defining the magnetic properties because it breaks the potential C4 symmetry of the resulting complexes. In this paper, we experimentally isolate the role of the water molecule by excluding it from the metal coordination sphere without altering the chemical structure of the ligand. Our complexes are therefore designed to be geometrically tetragonal and strict crystallographic symmetry is achieved by exploiting a combination of solution ionic strength and solid state packing effects. A thorough multitechnique approach has been used to unravel the electronic structure and magnetic anisotropy of the complexes. Moreover, the geometry enhancement allows us to predict, using only one angle obtained from the crystal structure, the ground state composition of all the studied derivatives (Ln = Tb to Yb). Therefore, these systems also provide an excellent platform to test the validity and limitations of the ab initio methods. Our combined experimental and theoretical investigation proves that the water molecule is indeed key in defining the magnetic anisotropy and the slow relaxation of these complexes.

Two-dimensional metal–organic nanosheets composed of single-molecule magnets: structural modulation and enhanced magnetism utilizing the steric hindrance effect

Tuning the bulkiness of the single-molecule magnet (SMM) alters the structures of SMM-nanosheets, which results in enhanced perpendicular magnetic anisotropy and SMM properties.

Carrier doping modulates the magnetoelectronic and magnetic anisotropic properties of two-dimensional MSi2N4 (M = Cr, Mn, Fe, and Co) monolayers.

Through extensive density functional theory (DFT) calculations, our investigation delves into the stability, electrical characteristics, and magnetic behavior of monolayers (MLs) of MSi2N4. Computational analyses indicate intrinsic antiferromagnetic (AFM) orders within the MSi2N4 MLs, as a result of direct exchange interactions among transition metal (M) atoms. We further find that CrSi2N4 and CoSi2N4 MLs with primitive cells (pcells) exhibit half-metallic properties, with respective spin-β electron gaps of 3.661 and 2.021 eV. In contrast, MnSi2N4 and FeSi2N4 MLs with pcells act as semiconductors, having energy gaps of 0.427 and 0.282 eV, respectively. When the SOC is considered, the CrSi2N4, MnSi2N4 and FeSi2N4 MLs are metals, while the CoSi2N4 ML is a semiconductor. Our findings imply the dynamics and thermodynamic stability of MSi2N4 MLs. We have also explored the influence of carrier doping on the electromagnetic attributes of MSi2N4 MLs. Interestingly, charge doping could transform CrSi2N4, MnSi2N4, and CoSi2N4 MLs from their original AFM state into a ferromagnetic (FM) order. Moreover, carrier doping transformed CrSi2N4 and CoSi2N4 MLs from spin-polarized metals to half-metals (HMs). It is of particular note that doping of CrSi2N4 MLs with +0.9 e per pcell or more holes caused a switch in the easy axis (EA) to the [001] axis. The demonstrated intrinsic AFM order, excellent thermodynamic and kinetic stability, adjustable magnetism, and half-metallicity of the MSi2N4 family suggest its promising potential for applications in the realm of spintronics.

Highly Anisotropic Magnetism and Nearly Isotropic Magnetocaloric Effect in Mn3Sn2 Single Crystals

Mn3Sn2 has been proposed as an ideal material for magnetic refrigeration. It undergoes two successive ferromagnetic transitions (T C1 = 262 K and T C2 = 227 K) and one antiferromagnetic transition (T N = 192 K). Herein we report, for the first time, the preparation of single crystals of Mn3Sn2 from Bi flux. The resultant anisotropic magnetic properties and magnetocaloric effect are investigated along the three principal crystallographic directions of the crystal. Significant anisotropy of magnetic susceptibility and multiple field-induced metamagnetic transitions were found at low fields, whereas the magnetocaloric effect was found to be almost isotropic and larger than that of the polycrystalline one. The maximum magnetic entropy change amounts to −ΔS M = 4.01 J⋅kg−1⋅K−1 near T C1 under a magnetic field change of μ 0ΔH = 5 T along the c-axis, with the corresponding refrigerant capacity of 1750 mJ⋅cm−3. Combined with a much wider cooling temperature span (∼ 80 K), our results demonstrate Mn3Sn2 single crystal to be an attractive candidate working material for active magnetic refrigeration at low temperatures.

Synthesis of Anisotropic Magnetic Polymeric Janus Particles by In Situ Separation of Magnetic Nanoparticles in a Microfluidic Device.

Magnetic Janus particles have been studied extensively for medical and biological applications owing to their controllable mobility in fluid media. In this work, we report a novel microfluidic device designed for the synthesis of magnetically anisotropic Janus particles made of poly(ethylene glycol) diacrylate and embedded with magnetic iron oxide nanoparticles. Our method consists of a droplet generation step followed by magnetic separation using an external magnetic field and ultraviolet polymerization. The synthesized particles exhibit a monodisperse size distribution with a standard deviation of less than 3.5%, which is among the best size distributions obtained in the literature for magnetic Janus particles. The anisotropic magnetic property of the particles enable them to rotate about their own axes in the presence of an external magnetic field, introducing another degree of freedom to their motion. This microfluidic technique is simple, one-step, and versatile, offering control over the size distribution to synthesize magnetically anisotropic Janus particles.

Giant coercivity induced by perpendicular anisotropy in Mn2.42Fe0.58Sn single crystals

We report the discovery of a giant out-of-plane coercivity in the Fe-doped Mn3Sn single crystals. The compound of Mn2.42Fe0.58Sn exhibits a series of magnetic transitions accompanying with large magnetic anisotropy and electric transport properties. Compared with the ab-plane easy axis in Mn3Sn, it switches to the c-axis in Mn2.42Fe0.58Sn, producing a sufficiently large uniaxial anisotropy. At 2 K, a giant out-of-plane coercivity (Hc) up to 3 T was observed, which originates from the large uniaxial magnetocrystalline anisotropy. The modified Sucksmith-Thompson method was used to determine the values of the second-order and the fourth-order magnetocrystalline anisotropy constants K1 and K2, resulting in values of 6.0 × 104 J/m3 and 4.1 × 105 J/m3 at 2 K, respectively. Even though the Curie temperature (TC) of 200 K for Mn2.42Fe0.58Sn is not high enough for direct application, our research presents a valuable case study of a typical uniaxial anisotropy material.

Combinatorial Growth of Vertically Aligned Nanocomposite Thin Films for Accelerated Exploration in Composition Variation

Combinatorial growth is capable of creating a compositional gradient for thin film materials and thus has been adopted to explore composition variation mostly for metallic alloy thin films and some dopant concentrations for ceramic thin films. This study uses a combinatorial pulsed laser deposition method to successfully fabricate two‐phase oxide–oxide vertically aligned nanocomposite (VAN) thin films of La0.7Sr0.3MnO3 (LSMO)‐NiO with variable composition across the film area. The LSMO‐NiO compositional gradient across the film alters the two‐phase morphology of the VAN through varying nanopillar size and density. Additionally, the magnetic anisotropy and magnetoresistance properties of the nanocomposite thin films increase with increasing NiO composition. This demonstration of a combinatorial method for VAN growth can increase the efficiency of nanocomposite thin film research by allowing all possible compositions of thin film materials to be explored in a single deposition.

Magnetic Ni‐Nanoinclusions in VO2 Thin Films for Broad Tuning of Phase Transition Properties

AbstractMott insulator VO2 exhibits an ultrafast and reversible semiconductor‐to‐metal transition (SMT) near 340 K (67 °C). In order to fulfill the multifunctional device applications, effective transition temperature (Tc) tuning as well as integrated functionality in VO2 is desired. In this study, multifunctionalities including tailorable SMT characteristics, ferromagnetic (FM) integration, and magneto‐optical (MO) coupling, have been demonstrated via metal/VO2 nanocomposite designs with controlled morphology, i.e., a two‐phase Ni/VO2 pillar‐in‐matrix geometry and a three‐phase Au/Ni/VO2 particle‐in‐matrix geometry. Evident Tc reduction of 20.4 to 54.9 K has been achieved by morphology engineering. Interestingly, the Au/Ni/VO2 film achieves a record‐low Tc of 295.2 K (22.2 °C), slightly below room temperature (25 °C). The change in film morphology is also correlated with unique property tuning. Highly anisotropic magnetic and optical properties have been demonstrated in Ni/VO2 film, whereas Au/Ni/VO2 film exhibits isotropic properties because of the uniform distribution of Au/Ni nanoparticles. Furthermore, a strong MO coupling with enhanced magnetic coercivity and anisotropy is demonstrated for both films, indicating great potential for optically active property tuning. This demonstration opens exciting opportunities for the VO2‐based device implementation towards smart windows, next‐generation optical‐coupled switches, and spintronic devices.

Patterns of the Formation of Mobile Localized Magnetic Configurations and Technology for Manufacturing Structures for the Implementation of Magnetic Memory Elements

Based on computer simulation and the analysis of technological, experimental, and theoretical results, the technological requirements for the formation of electronic devices based on magnetic vortices and skyrmions are formulated. The main types of interactions determined by technological factors are deter-mined. The design features of electronic devices based on magnetic vortices and skyrmions are studied. Various technological approaches to the fabrication of structures with different magnetic anisotropy properties are studied.

(Invited) An Overview of Electrochemistry Application to Additive Manufacturing

Additive manufacturing (AM) is the process of creating three-dimensional (3D) objects from digital models through the sequential deposition of material in layers. This talk will highlight how researchers have used electrochemical research in additive manufacturing and will provide insights into how technology can be exploited to formulate novel microstructures and optimize the manufacturing process. Electrochemical 3D printing is a relatively new form of AM that creates metallic structures through the electrochemical reduction of metal ions from solutions onto conductive substrates. It involves localized electrochemical deposition of metals combined with additive manufacturing principles to achieve Electrochemical Additive Manufacturing (ECAM). The talk will also focus on the formulation of metal precursor inks to produce novel metallic microstructures and nanoalloys containing multiple metals. These inks are used with AM techniques to fabricate 2D and 3D printed conductive structures directly onto a substrate. Examples include aligned nickel nanowires over large areas, which provide opportunities to produce structures with enhanced anisotropic electrical and magnetic properties. Nanoalloy films printed using metal precursor inks have a variety of important applications involving local control of alloy composition in AM part. Examples include the facile formation of layered nanostructures and electrical conductivity with oxidative stability. The talk will conclude with current research on electropolishing of AM parts. AM while capable of producing complex-shaped metal parts with intricate internal geometries and lattice structures struggles to make parts with the smooth surface finish required for many applications. Polishing interior surfaces inaccessible to traditional surface polishing methods is a challenge. Electropolishing is increasingly being used as a post-treatment option for metal AM parts due to its non-contact nature and ability to finish complex internal features.

Tunable Magnetic Domain Patterns in Thickness-Gradient Nickel Films on Flexible PDMS Substrates.

Flexible magnetoelectronic devices (based on magnetic films) have great application prospects in the fields of information storages, bionic robotics, and electronic skins. The intrinsic stress and external loading are very important to modulate the structures and properties of flexible magnetic films due to the magnetoelastic coupling effect. Here, we report on tunable magnetic domain patterns in thickness-gradient nickel (Ni) films deposited on flexible polydimethylsiloxane substrates. It is found that stripe magnetic domains spontaneously form in the Ni films and their sizes increase with the film thickness. The internal stress evolves from tensile to compressive states with decreasing film thickness, leading to the formation of cracks in thicker regions and wrinkles in thinner regions. Meanwhile, the orientations of stripe magnetic domains change from the gradient direction to the orthogonal direction. The structural features, evolution behaviors, and physical mechanisms of the cracks, wrinkles, and magnetic domains are analyzed based on the stress theory and magnetoelastic coupling. Periodic gradient Ni films with large-scale regulations of stripe magnetic domains are also realized by masking of copper grids. This study helps to better understand the magnetoelastic coupling effect in gradient flexible magnetic films and provides a technique to modulate anisotropic magnetic properties by designing specific film systems.

Magnetically-assisted digital light processing 4D printing of flexible anisotropic soft-Magnetic composites

ABSTRACT Flexible anisotropic soft-magnetic composite (FASMC) presents superior magnetic properties in one or more specified directions, showing great potential in the application of microwave absorption, soft robots, and other smart sensors/actuators. However, the fabrication of FASMC using additive manufacturing is challenging due to a trade-off between magnetic properties of the composites enhanced by iron particles and printability during printing. Here, we developed a 4D printing scheme using flexible soft-magnetic photosensitive resin consisting of flexible long-chin acrylic resin monomer and soft magnetic iron particles. Multiple complex structures with good spatial resolution of ∼170 μm were fabricated using magnetic field-assisted digital light processing (MF-DLP). Directional magnetic field was applied during printing, enabling the fabrication of FASMC with strong anisotropic magnetic properties. FASMC with high CIP (carbonyl iron powder, CIP) concentration of up to 45 wt.% was fabricated with excellent tensile strength and elongation up to 460%. Strong anisotropic magnetic properties were demonstrated through a series of stimuli-response testing such as large deformation, anti-deflection, controlled motion, variable stiffness metamaterial, and array assembly, under external magnetic field. This study demonstrates the feasibility and potential of MF-DLP technique for fabrication of FASMC, shedding light on the design and fabrication of next-generation sensors and actuators.

Facile preparation of bonded NdFeB/SmFeN hybrid magnets with flexibility, anisotropy and high energy density

The application of rubber isotropic bonded magnets is limited due to low energy density, although it remainsunbeatableintermsofprice and production rate. In this paper, high-filled, flexible, and anisotropic NdFeB/SmFeN bonded magnets were prepared using mixtures of fine SmFeN powders and coarse NdFeB powders by calendering molding. The optical microscope images show that adding fine SmFeN powder benefits processability, leading to higher loading while retaining flexibility. The magnetic property and microstructure of the magnets display the anisotropic magnetic property of NdFeB/SmFeN bonded magnets derived from the arrangement of the platelet-shaped NdFeB particles induced by mechanical stress during the calendaring process. To further optimize the magnetic properties of NdFeB/SmFeN bonded magnets, the NdFeB was sieved and then mixed with SmFeN to mold into sheets. Finally, the effect of NdFeB particle size on the magnetic and mechanical properties of NdFeB/SmFeN bonded magnets was investigated. The results showed that when the particle size of the NdFeB particle was 75–100 µm, the magnetic properties of magnets reached the maximum value (Br = 7.77 KG, Hcj = 14.70 KOe, (BH)max = 12.70 MGOe) with density of 5.59 g/cm3. In addition, the tensile strength of the NdFeB/SmFeN bonded magnets increases and the sample standard deviation narrows with decreasing NdFeB particle size. This method provides a facile preparation for anisotropic bonded magnets with a new energy density record of rubber bonded rolled magnets prepared without an external field.