Anisotropic Magnetic Behavior Research Articles

The Role of Rare-Earth Atoms in the Anisotropy and Antiferromagnetic Exchange Coupling at a Hybrid Metal-Organic Interface.

Magnetic anisotropy and magnetic exchange interactions are crucial parameters that characterize the hybrid metal-organic interface, a key component of an organic spintronic device. It is shown that the incorporation of 4f RE atoms to hybrid metal-organic interfaces of CuPc/REAu2 type (RE = Gd, Ho) constitutes a feasible approach toward on-demand magnetic properties and functionalities. The GdAu2 and HoAu2 substrates differ in their magnetic anisotropy behavior. Remarkably, the HoAu2 surface promotes the inherent out-of-plane anisotropy of CuPc, owing to the match between the anisotropy axis of substrate and molecule. Furthermore, the presence of RE atoms leads to a spontaneous antiferromagnetic exchange coupling at the interface, induced by the 3d-4f superexchange interaction between the unpaired 3d electron of CuPc and the 4f electrons of the RE atoms. It is shown that 4f RE atoms with unquenched quantum orbital momentum ( ), as it is the case of Ho, induce an anisotropic interfacial exchangecoupling.

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.

Hydrogen-annealing modulated magnetocaloric effect and critical behavior of Weyl semimetallic Co3Sn2S2

Modulating the electron interaction and magnetic domains is an essential strategy to evoke novel physical properties, both for fundamental research and for related magnetic applications. The emerging annealing process attracted attention due to its capability of tuning the magnetic performance, but it has been rarely studied. Herein, we conducted hydrogen annealing on the Weyl semimetallic Co3Sn2S2 and investigated the magnetic interaction, critical behavior, and magnetocaloric effect (MCE). Hydrogen-annealed Co3Sn2S2 (HA-Co3Sn2S2) exhibits a distinct anisotropy-dependent magnetic behavior, where a typical second-order transition with an easy magnetization process is observed under H//c. However, a frustrated magnetic state composed of ferromagnetic (FM), antiferromagnetic (AFM), and/or spin glass phases is observed when H//ab. Critical analyses illustrate that the ground state of HA-Co3Sn2S2 lies between the 3D-Ising model and the Mean-filed model, indicating the presence of both long-range and short-range magnetic interactions in the system. Additionally, we found that HA-Co3Sn2S2 exhibits an enhanced saturation magnetization (Ms) and magnetic refrigeration capacity, both showing anisotropic dependence, compared to the pristine Co3Sn2S2. Our work develops hydrogen annealing to modulate electron coupling and magnetic domains, paving the way for further studies of anisotropic magnetic behavior and applications in magnetic refrigeration.

Exploring the multifaceted properties of novel oxide-based perovskites ABO3 (A=Nd and B[dbnd]Lr, Y): A DFT study

The full-potential linear augmented plane wave with local orbital (FP-LAPW) technique is now used in this approach to better understand the structural, electronic, optical and mechanical properties of simple cubic oxide perovskite. NdLrO3 and NdYO3 compounds are studied by employing the density functional theory (DFT) with CASTEP code for the first time. The lattice parameters are found 4.2462 and 4.2301 Å for NdLrO3 and NdYO3 respectively. Both the compounds have 1.9 eV and 1.4 eV band gap showing the direct band gap nature of both materials. The exchange-correlation (XC) energy has been selected during this investigation with the Local Density Approximation (LDA) approach. We optimize as well as clarify the elastic constants Cij, the bulk modulus B, elasticity modulus G, Young's modulus of stretch Y, and the Poisson ratio v. Every substance shows anisotropic behavior. NdLrO3 and NdYO3 compounds exhibit a direct band-gap nature, as revealed by the electronic band structure computations. These compounds were all classified as semiconductors. To quantify the number of localized electrons in various bands, partial density of states (PDOS) and total density of states (TDOS) were deployed. Both compounds are computed by fitting the dispersion relation of the imagined component. Optical properties showed that these compounds were excellent absorbers of incident radiation. Therefore, it may be assumed that these compounds could be employed in magnetic sensors because of anisotropic magnetic behavior and to capture the ultraviolet range of solar radiations.

The influence of substrate orientation on the magnetic behavior of nearly-stoichiometric Mn5Ge3 thin films: DFT calculations and experimental analysis

The Mn5Ge3 exhibits a wide range of fascinating properties such as high spin polarization up to 42 %, large spin diffusion lengths, near-room Curie temperature, and possible integration with Ge, GaAs, and Si substrates. The influence of substrate orientation on magnetic behavior has been investigated. The thin films studied present an in-plane magnetic reversal which is isotropic in samples grown on GaAs(111) and anisotropic in samples grown on GaAs(001). Another difference observed is a linear trend to saturation on the out-of-plane hysteresis loop in samples grown on GaAs(111), comparatively to samples grown on GaAs(001). To better understand this scenario, Density Functional Theory (DFT) calculations were conducted. The results indicate a ferromagnetic metallic ground state with properties that are consistent with the experimental results. The projected densities of states indicate that the main responsible for the magnetic moment observed in the Mn5Ge3 is the Mn-Mn interaction. The magnetic field distribution isosurfaces obtained from the DFT calculations offer a satisfactory explanation of the magnetic reversal experimentally observed, especially the in-plane magnetic behavior in samples grown on both GaAs(111) and GaAs(001) substrates. This work provides a theoretical-experimental approach that allows a deeper understanding of the magnetic anisotropy behavior under the influence of the crystallographic orientation of the substrate observed in nearly-stoichiometric Mn5Ge3 thin films, which is a good candidate for rare-earth free magnet in spintronic applications.

Non-coplanar spin structure in a metallic thin film of triangular lattice antiferromagnet CrSe

An antiferromagnetic metal with a two-dimensional triangular network offers a unique playground of intriguing magneto-transport properties and functionalities stemming from the interplay between conducting electrons and intricate magnetic phases. A NiAs-type CrSe is one of the candidates owing to alternate stackings of Cr and Se triangular atomic networks in its crystal structure. While the fabrication of CrSe thin films is indispensable to develop functional devices, studies on its thin-film properties have been limited to date due to the lack of metallic samples. Here, we report on the realization of metallic conductivities of CrSe thin films, which allows us to investigate their intrinsic magneto-transport properties. The metallic sample exhibits a co-occurrence of weak ferromagnetism with perpendicular magnetic anisotropy and antiferromagnetic behavior, indicating the presence of non-coplanar spin structures. In addition, control of the polarity and tilting angle of the non-coplanar spin structure is accomplished by a sign of cooling magnetic fields. The observed non-coplanar spin structure, which can be a source of emergent magnetic field acting on the conducting electrons, highlights the high potential of the triangular lattice antiferromagnet and provides a unique platform for functional thin-film devices composed of NiAs-type derivative Cr chalcogenides and pnictides.

Exploring anisotropic phases and spin transport in perovskite heterostructures: Insights into 3d/5d interfaces for antiferromagnetic spintronics

Transition metal oxides (TMOs) demonstrate a broad spectrum of properties encompassing electronic correlations, anisotropic transport, magnetism, and optical behavior. The anisotropy arises from both intrinsic crystal symmetry and extrinsic factors like epitaxial strain and structural asymmetry at TMO interfaces. Weiss and Neel's work has elucidated anisotropic magnetic behavior in antiferromagnetic (AFM) materials. AFM TMOs exhibit unique magnetotransport behavior, including weak antilocalization (WAL) and anisotropic magnetoresistance (AMR). Understanding the magnetic structure and band topology in AFM perovskites and their interfaces enables the tailored design of materials for spintronics and energy conversion. In few interfaces lacking inversion symmetry, Rashba spin–orbit coupling (SOC) induces WAL, a quantum correction in conductivity in a two-dimensional electronic system. Electron accumulation and charge transfer across 3d, 5d transition metal-based perovskite interfaces affect WAL and AMR, as observed in 3d/3d and 3d/5d AFM heterostructures, respectively. Advancements in spintronics rely on exploring spin-dependent transport anisotropy. This review focuses on various scattering mechanisms, categorized as extrinsic and intrinsic, in anisotropic transport, particularly in 3d/5d AFM superlattices. The WAL scattering mechanism depends on both intrinsic factors related to Rashba SOC-induced band topology and extrinsic sources like spin impurities and lattice ions. Moreover, the investigation into AMR mechanisms involves the application of impurity-based extrinsic scattering models, which are aligned with the Rashba and Dresselhauss models on Fermi surfaces. This exploration specifically targets the interface of two-band insulators, exemplified by LaAlO3/SrTiO3 and LaVO3/KTaO3. Furthermore, this model achieves comprehensive coverage, extending its applicability to 3d/5d AFM heterostructures like LaMnO3/SrIrO3 and CaMnO3/CaIrO3. Additionally, the intrinsic scattering mechanism tied to Berry phase effects related to band topology is studied, focusing on the CaMnO3/CaIrO3 superlattice. Despite manipulation challenges stemming from reduced stray fields, AFM materials show potential in interface physics and applications within the realm of spintronics.

Influence of composition on the structural, magnetic and magnetotransport properties of nanostructured Co-Ag films fabricated by electrodeposition technique

Evolution of structure, granular size, magnetoresistance and magnetization behavior of electrodeposited Co-Ag coatings with changing cobalt concentration from 19.07 to 47.02 at.% is offered. The heterogeneity of the deposits was verified through the utilization of structural techniques, including X-ray diffraction and transmission electron microscopy, revealing a size distribution ranging from superparamagnetic to ferromagnetic particles. The coatings were found to contain both fcc-Ag and fcc-Co. As the concentration of Co in the films increases, the size of the magnetic granules also increases while the distance among them simultaneously is reduced. The magnetic force microscopy indicates that magnetic domains exist which are significantly larger than actual particles. The highest giant magnetoresistance (GMR) amplitude was observed in coatings with a cobalt concentration of 33. 12 at. %. The studies on dc-magnetization obviously recognized the existence of perpendicular magnetic anisotropy. With increasing cobalt concentration beyond 33.12 at. %, the strength of perpendicular magnetic anisotropy decreases, while the anisotropic magnetoresistance (AMR) increases. The observed perpendicular magnetic anisotropy and complex magnetoresistance behavior in the Co-Ag films can be explained by the transition in the nature of magnetic interaction from dipolar to ferromagnetic interactions. Moreover, results indicate that the coercivity of Co-Ag films decreases with increasing the Co concentration up to 33.12 at. %, but begins to increase with further increasing Co concentration in the Co-Ag coatings. we calculated the first and second magnetic anisotropy factors based on the magnetization curves.

Investigation on crystallographic alignment of Sm-Co alloy nanoparticles by external magnetic field

In order to improve the magnetic properties of Sm-Co nanopowder prepared using the low oxygen-induction thermal plasma (LO-ITP) process, the effect of heat treatment on the phase transformation and magnetic properties of Sm-Co nanopowder was investigated. Sm-Co nanopowder was annealed at 873, 973, 1073, and 1173 K. The X-ray diffraction results indicate that uniform Sm-Co nanopowder with a dominant SmCo5 phase can be prepared at annealing temperatures higher than 1073 K. The coercivity of the Sm-Co nanopowder annealed at 1173 K was measured to be 1.5 MA/m. The Sm-Co nanoparticles can be sufficiently oriented using an external magnetic field. Although perfect crystal orientation could not be achieved in the annealed nanopowder owing to necking, short-duration heat treatment promoted the formation of the hard magnetic phase and suppressed necking. The results of this study demonstrate the importance of the rapid heat treatment effect during particle formation in the ITP process for preparing dispersible Sm-Co nanoparticles with high coercivity and improved anisotropic magnetic behavior.

Anomalous Magnetic Anisotropy Behaviour in Co-Rich and Fe-Rich Glass-Coated Microwires under Applied Stress.

In this article, we study the effect of annealing temperature and applied stress on the magnetic properties of Fe71.80B13.27Si11.02Nb2.99Ni0.92 and Co65.34Si12.00B10.20Cr8.48Fe3.90Mo0.08 microwires. An anomalous behavior of the coercive field is observed while applying stress, indicating nontrivial changes in the microwire magnetic anisotropy. The effect of applied stimuli on the magnetic anisotropy and magnetostriction constant in both microwires is also discussed.

Thickness dependent magnetic anisotropy studies in sputtered Fe-Co-Al thin films

In this paper, an attempt has been made to evolve a structure-magnetic microstructure – magnetic property correlations in sputtered Fe-Co-Al thin films grown at different thicknesses. Fe-Co-Al thin films with various thicknesses viz., 25, 50, 100, 150 and 200 nm were deposited on Si 〈100〉 substrates at room temperature. Structural studies revealed that the films are crystalline in nature with bcc type structure. The crystallinity and average crystallite size deduced from X-ray diffraction studies were found to increase with increase in film thicknesses. Surface microscopy investigations also showed an increase in grain size with film thickness. All the films exhibited a predominant in-plane (IP) magnetic anisotropy. While the saturation magnetization was found to decrease with increase in film thickness, the coercivity exhibited an increasing trend. A maximum saturation magnetization of about 1300 emu/cc has been realized for the 50 nm thick film. Angular dependent magnetization studies indicated anisotropic magnetic behaviour along the plane of the film. Magnetic microscopy studies carried out using Longitudinal magneto-optical Kerr microscopy showed presence of 180° band domain along the easy direction of magnetization for lower thickness films. With subsequent increase in film thickness a combination of ripple and band domains were observed. With further increase in film thickness, presence of only ripple domains has been observed. The deterioration of IP magnetic properties with increase in film thickness was correlated with the magnetic microstructural observations.

Enhanced magnetic anisotropy and Single-chain magnet behavior via Photo-induced charge transfer

Enhanced magnetic anisotropy and Single-chain magnet behavior via Photo-induced charge transfer

Structural and Magnetic Properties of Ni Nanoparticles Embedded in Vinyl Polymer Nanocomposite Films

Ni nanoparticles layer of nominal thickness in the range of 5–40[Formula: see text]nm were deposited on polyvinyl alcohol (PVA) film by using the ion beam sputtering (IBS) technique. PVA films were made on a quartz substrate by the solution casting technique. Grazing incidence X-ray diffraction (GIXRD) results reveal Ni is present in a metallic form in the FCC phase. AFM shows that roughness increases with increase in thickness of Ni layer and corresponding MFM images of magnetic domains were recorded. Soft X-ray absorption spectroscopy (SXAS) studies on the PVA/Ni nanocomposites films were recorded using synchrotron radiation. This study is used to study the electronic structure of the as-prepared nanocomposite films and reveals that Ni nanoparticles are present in their metallic form. Magnetic properties were measured using the magneto-optical Kerr effect (MOKE) magnetometer and the films were found to be magnetically soft with higher value of coercivity at lower thickness of Ni nanoparticles layer. The results of magnetic studies are discussed in light of the microstructure and morphological features of PVA/Ni nanocomposite films. The PVA/Ni nanocomposites showed interesting anisotropic magnetic behavior; thus the investigative results may be useful for the development of futuristic flexible functional magnetic material system.

Nanostructuring of Rare-earth-based Single-Molecule Magnets as Long-range Ordered Arrays in the Framework of Organic Metal Halide Perovskites.

The nanostructuring of single-molecule magnets (SMMs) on substrates, in nanotubes and periodic frameworks is highly desired for the future magnetic recording devices. However, the ability to organize SMMs into long-range ordered arrays in these systems is still lacking. Here, we report the incorporation of magnetic (RECl2 (H2 O)6 )+ (RE=rare earths) molecular groups into the framework of an organic metal halide perovskite (OMHP)-(H2 dabco)CsCl3 . Intriguingly, we show the incorporated rare-earth groups self-organized into long-range ordered arrays that uniformly and periodically distributed in the A sites of OMHP. The ordered (RECl2 (H2 O)6 )+ groups serve as SMMs in the perovskite frameworks, exhibiting large effective magnetic moment, moderate magnetic anisotropy and two-step relaxation behavior. With the additional merit of great structural flexibility and multifunction of OMHPs, the preparation of the first SMMs@OMHP magnetic materials furthers the development of molecular spintronics.

Defects modify anisotropic saturation magnetization in transparent and flexible Hf0.95Co0.05O2 thin films for wearable device

A pure inorganic flexible magnetic thin film that is transparent with high temperature and light weight is crucial for high temperature flexible/wearable magnetic sensors and spintronics devices such as electronic skin and a mechanical arm. Here, a transparent flexible Hf0.95Co0.05O2 (HCO) thin film with various thicknesses of 105, 140, 175, and 210 nm was deposited on fluorophlogopite (F-Mica) substrates by using a sol-gel method. All of the flexible HCO samples show two phase structures with a monoclinic phase (M-phase) and an orthorhombic phase (O-phase), resulting in strain and strain relaxation in the samples of different thicknesses. An out-of-plane anisotropy behavior in saturation magnetization was observed in the flexible HCO samples, and the values of (Ms-out-of-plane−Ms-in-plane) decrease with the increase in the thickness. The content of Co2+ increases and the content of Co3+ and vacancy oxygen decrease when the thickness increases, which will affect the anisotropic magnetization behavior in the flexible HCO thin films. Moreover, the flexible HCO samples show excellent light transparency (above 80% in the visible range). The flexible HCO thin films with an anisotropic magnetization behavior and high transmittance are promising for various applications in transparent flexible/wearable devices.

Anisotropic magnetotransport in the layered antiferromagnet TaFe1.25Te3

The discovery of fascinating ways to control and manipulate antiferromagnetic materials have garnered considerable attention as an attractive platform to explore novel spintronic phenomena and functionalities. Layered antiferromagnets (AFMs) exhibiting interesting magnetic structures can serve as an attractive starting point to establish novel functionalities down to the two-dimensional limit. In this work, we explore the magnetoresistive properties of the spin-ladder AFM ${\mathrm{TaFe}}_{1.25}{\mathrm{Te}}_{3}$. Magnetization studies reveal an anisotropic magnetic behavior resulting in the stabilization of a spin-flop configuration for $H\ensuremath{\perp}$ (10-1) plane (i.e., out-of-plane direction). Angle-dependent longitudinal and transverse magnetoresistances show an unusual anharmonic behavior. A significant anisotropic enhancement of magnetoresistance when $H\ensuremath{\perp}$ (10-1) plane compared to $H||$ (10-1) directions has been observed. The present results deepen our understanding of the magnetoresistive properties of low-dimensional layered AFMs, and point towards the possibility of utilizing these novel material systems for antiferromagnetic spintronics.

Manufacturing of Textured Bulk Fe-SmCo5 Magnets by Severe Plastic Deformation.

Exchange-coupling between soft- and hard-magnetic phases plays an important role in the engineering of novel magnetic materials. To achieve exchange coupling, a two-phase microstructure is necessary. This interface effect is further enhanced if both phase dimensions are reduced to the nanometer scale. At the same time, it is challenging to obtain large sample dimensions. In this study, powder blends and ball-milled powder blends of Fe-SmCo5 are consolidated and are deformed by high-pressure torsion (HPT), as this technique allows us to produce bulk magnetic materials of reasonable sizes. Additionally, the effect of severe deformation by ball-milling and severe plastic deformation by HPT on exchange coupling in Fe-SmCo5 composites is investigated. Due to the applied shear deformation, it is possible to obtain a texture in both phases, resulting in an anisotropic magnetic behavior and an improved magnetic performance.

Critical behavior and strongly anisotropic interactions in PrMn2Ge2

Understanding the mechanisms for forming skyrmionic spin configurations at room temperature is essential for exploring the applicable spintronics devices based on topological spin textures. In this work, the anisotropic magnetic properties and critical behavior are investigated in noncollinear itinerant magnet PrMn2Ge2. The strongly anisotropic magnetic interactions and magnetic field and temperature induced antiferromagnetic to ferromagnetic transition are observed. The critical behavior of high temperature ferromagnetic transition at 331 K was analyzed, and the critical exponents β = 0.335, γ = 0.878, and δ = 3.617 are extracted by the modified Arrott plot method, which lie between the values of long-range mean-field and short-range three-dimensional theories, demonstrating that PrMn2Ge2 possesses multiple magnetic interactions. This is also confirmed by the moderated interaction function, which is decay as J(r) ∼ r−4.69. Therefore, the competition of multiple magnetic interactions in PrMn2Ge2 is analogous to what has been observed in GdRu2Si2 and could be the origin of skyrmionic bubbles observed at room temperature.

Effect of surfactants on the stability, rheological properties, and thermal conductivity of Fe3O4 nanofluids

Stability is the major factor that enables the application of nanofluids in energy conversion systems. Excellent rheological and thermal conductivity is the key for nanofluids to be an ideal heat transfer medium. In this work, we investigated the stability of Fe3O4 nanofluids by four characterization techniques, mainly from the viewpoint of surfactant type and mass ratio, and systematically studied its rheological and thermal conductivity properties by different experimental methods and analyzed the behavior of magnetic fluid thermal anisotropy by mathematical methods. The experimental results show that the surfactant Tetramethylammonium hydroxide (TMAH) has the best stability effect and can keep the Fe3O4 nanofluids more than 120 h. And the best ratio is when the mass ratio of Fe3O4 to TMAH is 1:4. The surfactant Polyvinylpyrrolidone (PVP) has the greatest effect on nanofluids viscosity. The increase in TMAH mass leads to a Newtonian fluid behavior of the nanofluids at low temperatures and low shear rates, besides shifting its shear thinning towards the high temperature region. However, from the curve relationship between the shear rate and shear stress, the Fe3O4 nanofluids belongs to the expansion fluid among non-Newtonian fluids. The surfactant Sodium dodecyl sulfate (SDS) have the greatest effect on the thermal conductivity of Fe3O4 nanofluids. Theoretical calculations show that as the concentration increases, the rate of heat transfer in the direction of the parallel magnetic field is significantly greater than in the direction of the perpendicular magnetic field, while the rate of heat transfer in the absence of a magnetic field is somewhere in between.

Valley polarization, magnetic anisotropy and band alignment engineering in two-dimensional 2H-VTe2/1T-FeCl2 van der Waals heterostructures

The effects of stacking configurations, biaxial strain, and layer distance on the valley polarization and band alignment of 2H-VTe2/1T-FeCl2 van der Waals heterostructures are investigated through the first-principles calculations. The results predict that magnetic anisotropy behavior with its easy magnetization axis stability keeps in-plane with altering stacking orders and biaxial strain from −6% to 6%. The valley polarization of 2H-VTe2 is well preserved in the 2H-VTe2/1T-FeCl2 heterostructures, and the most stable stacking configuration with type-I band alignment exhibits a large valley polarization of 156.5 meV, which can realize a maximum valley polarization of 166.6 meV at the compression strain of −4%. The biaxial strain remarkably alters the band structure of heterostructures and achieves the transitions from type-I to type-II and III band alignments as well as from semiconductor to metallic. The modulation of layer distance shows a weak effect on valley polarization and only can convert the band alignment from type-I to type-II. The significant variations of band alignments enable 2H-VTe2/1T-FeCl2 heterostructure to become an attractive candidate for optoelectronic and photocatalytic materials and also give rise to the possibility of valleytronics and spintronics application.