Ferromagnetic Metal Research Articles

Robust half metallic properties in two-dimensional transition metal borocarbides: TMBC (TM = 3d transition metals)

Two-dimensional transition metal borocarbides with intrinsic magnetism have garnered significant research attention due to their potential applications in spintronics. Using density functional theory calculations, we designed a type of transition metal borocarbides with two distinct configurations, TMBC-Is and TMBC-IIs (TM = V–Co), and explored their electronic and magnetic properties. Our results demonstrate that all the studied systems exhibit both thermal and kinetic stability. Notably, four systems of MnBC-I/MnBC-II and FeBC-I/FeBC-II are robust ferromagnetic (FM) half metals (HMs) with Curie temperatures of 145, 180, 108, and 315 K. Expect FeBC-II monolayer, FM to antiferromagnetic transition occurs for three other FM HMs under 8%–10% compressive strains, while FM HM to FM semiconductor transition is found for MnBC-II monolayer under 8% tensile strain. These findings provide a promising way to design two-dimensional FM HMs, which hold potential applications in spintronics.

Unconventional magnetotransport properties of two-dimensional ferromagnet Fe5GeTe2

Two-dimensional (2D) van der Waals FexGeTe2 metallic ferromagnets have Curie temperature near or even higher than room temperature, showing great prospects in the field of spintronics. Here, we study the magnetotransport properties of Fe5GeTe2 nanoflakes. Multiple sign changes of angle-dependent magnetoresistance (ADMR) are observed with changing temperature or magnetic field. The high field-induced negative to positive MR transition in low temperatures (T < 50 K) and the temperature-induced sign reversal of anisotropic MR at T = 130 K are responsible for these exotic and complex characteristics of ADMR. In addition, the electron–magnon scattering induced negative MR exhibits abnormal nonmonotonic temperature dependence, which is related to the nonmonotonic variation of anomalous Hall resistance and the transition of the carrier types at T = 150 K. The exotic magnetotransport properties of Fe5GeTe2 revealed in this work may help pave the way for the practical application of this 2D magnetic material.

Highly Efficient Room-Temperature Spin-Orbit-Torque Switching in a Van der Waals Heterostructure of Topological Insulator and Ferromagnet.

All-Van der Waals (vdW)-material-based heterostructures with atomically sharp interfaces offer a versatile platform for high-performing spintronic functionalities at room temperature. One of the key components is vdW topological insulators (TIs), which can produce a strong spin-orbit-torque (SOT) through the spin-momentum locking of their topological surface state (TSS). However, the relatively low conductance of the TSS introduces a current leakage problem through the bulk states of the TI or the adjacent ferromagnetic metal layers, reducing the interfacial charge-to-spin conversion efficiency (qICS). Here, a vdW heterostructure is used consisting of atomically-thin layers of a bulk-insulating TI Sn-doped Bi1.1Sb0.9Te2S1 and a room-temperature ferromagnet Fe3GaTe2, to enhance the relative current ratio on the TSS up to ≈20%. The resulting qICS reaches ≈1.65 nm-1 and the critical current density Jc ≈0.9×106Acm-2 at 300 K, surpassing the performance of TI-based and heavy-metal-based SOT devices. These findings demonstrate that an all-vdW heterostructure with thickness optimization offers a promising platform for efficient current-controlled magnetization switching at room temperature.

Investigating the shunting effect in a Fe/Co ferromagnetic metal hybrid structure and its impact on the spin Seebeck effect

Investigating the shunting effect in a Fe/Co ferromagnetic metal hybrid structure and its impact on the spin Seebeck effect

Critical enhancement of the spin Hall effect by spin fluctuations

The spin Hall (SH) effect, the conversion of the electric current to the spin current along the transverse direction, relies on the relativistic spin-orbit coupling (SOC). Here, we develop a microscopic theory on the mechanisms of the SH effect in magnetic metals, where itinerant electrons are coupled with localized magnetic moments via the Hund exchange interaction and the SOC. Both antiferromagnetic metals and ferromagnetic metals are considered. It is shown that the SH conductivity can be significantly enhanced by the spin fluctuation when approaching the magnetic transition temperature of both cases. For antiferromagnetic metals, the pure SH effect appears in the entire temperature range, while for ferromagnetic metals, the pure SH effect is expected to be replaced by the anomalous Hall effect below the transition temperature. We discuss possible experimental realizations and the effect of the quantum criticality when the antiferromagnetic transition temperature is tuned to zero temperature.

Synthesis of Co@N-doped carbon with yolk–shell heterostructures for efficient electromagnetic wave absorption

Regulating the composition and microstructure of nanomaterials is a major challenge in the development of high-performance materials for electromagnetic wave (EMW) absorption. This paper introduces a new lightweight EMW-absorbing material Co@N/C with a yolk–shell structure and compositions of ferromagnetic metal and carbon materials. The minimum reflection loss (RLmin) of the as-designed Co@N/C nanospheres with a filler loading of 25 wt% reaches −67.68 dB and the effective absorption bandwidth of a 1.9 mm thickness is 5.3 GHz. The exceptional absorption performance of the EMW absorption is primarily achieved through the synergistic effect between the Co–carbonaceous material and the yolk–shell structure, which optimizes the impedance matching. The polarization loss, conductivity loss, magnetic loss, and multiple scattering mainly contribute to the excellent EMW-absorption ability of the materials. The proposed method for regulating the structure and morphology of Co@N/C can efficiently construct high-performance EMW absorbers.

Martensitic Transition and Electronic, Magnetic, Thermal, and Thermoelectric Properties of Metallic Ferromagnetism Ni2Mn1-xGa1-yFex+y Shape Memory Alloys: Ab Initio Calculations

Martensitic Transition and Electronic, Magnetic, Thermal, and Thermoelectric Properties of Metallic Ferromagnetism Ni2Mn1-xGa1-yFex+y Shape Memory Alloys: Ab Initio Calculations

Enhancement of spin to charge conversion efficiency at the topological surface state by inserting normal metal spacer layer in the topological insulator based heterostructure

In this study, we report efficient spin to charge conversion (SCC) in the topological insulator (TI) based heterostructure (BiSbTe1.5Se1.5/Cu/Ni80Fe20) by using spin-pumping technique, where BiSbTe1.5Se1.5 is the TI and Ni80Fe20 is the ferromagnetic (FM) layer. The SCC, characterized by inverse Edelstein effect length (λIEE) in the TI material, gets altered with an intervening Copper (Cu) layer, and it depends on the interlayer thickness. The introduction of Cu layer at the interface of TI and FM metal provides a new degree of freedom for tuning the SCC efficiency of the topological surface states. The significant enhancement of the measured spin-pumping voltage and the increased linewidth of ferromagnetic resonance absorption spectra due to the insertion of Cu layer at the interface indicate a reduction in spin memory loss at the interface that resulted from the presence of exchange coupling between the surface states of TI and the local moments of FM metal. The temperature dependence (from 8 to 300 K) of the evaluated λIEE data for all the trilayer systems, TI/Cu/FM with different Cu thicknesses, confirms the effect of exchange coupling between the TI and FM layer on the SCC efficiency of the topological surface state. This study offers promising ways for designing more efficient spin-charge conversion devices of the TI-based heterostructure by controlling the interface effects.

Room‐temperature tunable tunneling magnetoresistance in Fe3GaTe2/WSe2/Fe3GaTe2 van der Waals heterostructures

AbstractThe exceptional properties of two‐dimensional (2D) magnet materials present a novel approach to fabricate functional magnetic tunnel junctions (MTJ) by constructing full van der Waals (vdW) heterostructures with atomically sharp and clean interfaces. The exploration of vdW MTJ devices with high working temperature and adjustable functionalities holds great potential for advancing the application of 2D materials in magnetic sensing and data storage. Here, we report the observation of highly tunable room‐temperature tunneling magnetoresistance through electronic means in a full vdW Fe3GaTe2/WSe2/Fe3GaTe2 MTJ. The spin valve effect of the MTJ can be detected even with the current below 1 nA, both at low and room temperatures, yielding a tunneling magnetoresistance (TMR) of 340% at 2 K and 50% at 300 K, respectively. Importantly, the magnitude and sign of TMR can be modulated by a DC bias current, even at room temperature, a capability that was previously unrealized in full vdW MTJs. This tunable TMR arises from the contribution of energy‐dependent localized spin states in the metallic ferromagnet Fe3GaTe2 during tunnel transport when a finite electrical bias is applied. Our work offers a new perspective for designing and exploring room‐temperature tunable spintronic devices based on vdW magnet heterostructures.

Anomalous electrons in a metallic kagome ferromagnet

Ordinary metals contain electron liquids within well-defined ‘Fermi’ surfaces at which the electrons behave as if they were non-interacting. In the absence of transitions to entirely new phases such as insulators or superconductors, interactions between electrons induce scattering that is quadratic in the deviation of the binding energy from the Fermi level. A long-standing puzzle is that certain materials do not fit this ‘Fermi liquid’ description. A common feature is strong interactions between electrons relative to their kinetic energies. One route to this regime is special lattices to reduce the electron kinetic energies. Twisted bilayer graphene1–4 is an example, and trihexagonal tiling lattices (triangular ‘kagome’), with all corner sites removed on a 2 × 2 superlattice, can also host narrow electron bands5 for which interaction effects would be enhanced. Here we describe spectroscopy revealing non-Fermi-liquid behaviour for the ferromagnetic kagome metal Fe3Sn2 (ref. 6). We discover three C3-symmetric electron pockets at the Brillouin zone centre, two of which are expected from density functional theory. The third and most sharply defined band emerges at low temperatures and binding energies by means of fractionalization of one of the other two, most likely on the account of enhanced electron–electron interactions owing to a flat band predicted to lie just above the Fermi level. Our discovery opens the topic of how such many-body physics involving flat bands7,8 could differ depending on whether they arise from lattice geometry or from strongly localized atomic orbitals9,10.

Electric manipulation of the magnetization in heterostructure Pt/Co/Bi2Se3

Spin–orbit torque (SOT) can provide efficient electrical manipulation of magnetism via applying electrical current to breaking the symmetry of damping-like torque. In the heterojunction of heavy and ferromagnetic metal, Dzyaloshinskii–Moriya interaction (DMI) is one of the key ingredients for stabilizing chiral spin structures, like chiral domain walls. Meanwhile, materials with larger charge-spin conversion rates are also highly expected for the efficient SOT. In this paper, spin–orbit torque magnetic switching is observed in the perpendicularly magnetized Pt/Co/Bi2Se3 and shows relatively high efficiency with low critical switching current density of about 5 × 105 A cm−2. The SOT efficiency and DMI in perpendicularly magnetized Pt/Co/Bi2Se3 were quantitatively investigated by electrical detection of the effective spin Hall field. The DMI constant is about 2.6 mJ m−2, and the effective spin Hall angle of Pt/Co/Bi2Se3 is about 0.14. The work also demonstrates that the Bi2Se3 layer takes the main responsibility for SOT, and the Pt/Co interface is the main source of DMI in Pt/Co/Bi2Se3 structures, which makes it possible to achieve independent optimization of DMI and SOT in the Pt/Co/Bi2Se3 structure at room temperature for the advanced application of spintronic devices.

Investigation of ordered dispersive effect, charge density, thermal properties and disappearance of spin polarization in perovskite CsBeO3 under the influence of pressure-A DFT perspective

Full Potential Linearized Augmented Plane Wave method (FP-LAPW) was employed to investigate the behavior of cubic perovskite CsBeO3 under the influence of pressure. The spin polarized study has been carried out in PBE-GGA approximation under the application of pressure. The variation of pressure is attained by the appropriate reduction of volume for the compound. At equilibrium volume and at 0 GPa, the compound CsBeO3 is found to exhibit energy gap in the spin up direction and the spin down direction is largely conducting. With the reduction of volume and their corresponding increase in pressure, the electronic behavior changes for the compound. At a pressure of about 10 GPa, the s-orbital of Cs atom undergoes energy excitation to higher energy level due to an ordered dispersive effect at s-orbital. This results in the disappearance of energy gap and the compound becomes conducting in spin up direction and the half metallic ferromagnetism is found to disappear at increased pressure. Thermal properties such as Debye temperature and Curie point have been reported in this work. Elastic constants and anisotropy factor have been determined and compared at different pressures.

Research on Experimental Bench Testing of Wear Metal Particles in Lubricating Oil Based on Self-Excitation and Self-Induction of Coil

The on-line monitoring of wear metal particles in lubricating oil plays an important role in equipment fault diagnosis technology. According to the principle of electromagnetic induction and the Biot-Savart law, model structure design, coil production, etc., different from traditional multi-coil excitation detection methods and compared to traditional methods that are only sensitive to large particles, this paper designed a self-excitation and self-induction metal particle monitoring sensor in lubricating oil based on LC resonance. At the same time, a sensor experimental bench is built by combining the production of ferromagnetic and non-ferromagnetic metal particle standards. In addition, through experimental verification, the sensor can achieve monitoring sensitivity for ferromagnetic particles greater than 41.28 μm and non-ferromagnetic (copper) particles greater than 61.53 μm under the 4.2 mm aperture flow channel, realizing the sensitivity on monitoring of small wear ferromagnetic particles and wear metal non-ferromagnetic particles, the experiment showed that it is particularly sensitive to small non-ferromagnetic particles. Based on a wide pipeline radius, the accuracy and sensitivity of the designed single-coil sensing system have been demonstrated.

Ciecz buforowa i metoda jej przygotowania w celu wykonania korków cementowych

The study of extensive material on the results of well cementing in various regions of the world shows that the quality of plugging operations is largely determined by the degree of displacement of the drilling fluid from the well. No one has ever specifically developed a buffer fluid for plugback cementing. When carrying out reverse cementing, determining the end time of the cementing process is of great importance, which largely depends on the choice of buffer fluid. The purpose of this work is to give the buffer fluid the properties of a magnetic locking element during plugback cementing of casing strings while increasing its separating ability. To achieve this, carboxymethyl cellulose is additionally dissolved in water before the displacement of the components when preparing a buffer liquid. Rubber crumbs are then mixed with the filler, and mixing is carried out under a pressure of at least 0.2 MPa. The buffer liquid contains the following components in the following wt.% ratios: carboxymethylcellulose 4–5, crumb rubber 7–8, ferromagnetic metal powder 15–16, with the remaining portion being water. The buffer fluid of the optimal composition not only maintains no less (than 98%) displacing power, but also exhibits an exceptionally low filler fall rate (when diluted by half). Furthermore, it does not linger in a pipe with an open end and an annular magnet inside, preventing settling plugs. The economic benefits of using a buffer fluid primarily stems from ensuring reliable control over the filling of the annular space with cement slurry, preventing its pumping from the annulus to the intracasing space, and preventing clogging of the productive underlying formation with cement.

Photovoltaic effect on silicon–alumina–ferromagnet tunnel junction providing insights about spin-dependent molecular spintronics solar cells

The study focuses on the observation of the photovoltaic (PV) effect on Si/AlOx/FM semiconductor–insulator–ferromagnetic metal (SIFM) structure. Utilization of ∼10 nm NiFe film as the top ferromagnet (FM) layer was permeable for sufficient light radiation necessary for reaching the silicon substrate for the generation of electron–hole pairs upon photoexcitation. The effect of light intensity and magnetic field was studied on the SIFM’s PV response. We also investigated the role of silicon doping and the AlOx tunnel barrier between Si and FM in exploring suitable band bending necessary for separating the electron–hole pairs. Increasing the dopant density in Si and a damaged AlOx tunnel barrier quenched the PV effect. Ferromagnet/Insulator/Ferromagnet (FMIFM) was also studied to gain deeper mechanistic insights into the spin-dependent photovoltaic effect observed on FM/AlOx/FM tunnel junction-based molecular spintronics devices. Bridging of magnetic molecules between the Si and FM electrodes of SIFM increased the overall device current by establishing additional parallel conduction channels along with the AlOx tunnel barrier. However, SIFM with molecular conduction channels did not produce a PV effect. This study reported the PV effect on well-designed SIFM and opened possibilities for exploring new systems. More importantly, this paper provided insights into the role of molecule-induced exchange coupling in transforming an ordinary, cheap, and widely available ferromagnet into a semiconductor-like material capable of showing PV.

Thermoelectric and magneto-transport characteristics of interconnected networks of ferromagnetic nanowires and nanotubes

Macroscopic-scale nanostructures, situated at the interface of nanostructures and bulk materials, hold significant promise in the realm of thermoelectric materials. Nanostructuring presents a compelling avenue for enhancing material thermoelectric performance as well as unlocking intriguing nanoscale phenomena, including spin-dependent thermoelectric effects. This is achieved while preserving high power output capabilities and ease of measurements related to the overall macroscopic dimensions. Within this framework, the recently developed three-dimensional interconnected nanowire and nanotube networks, integrated into a flexible polymer membrane, emerge as promising candidates for macroscopic nanostructures. The flexibility of these composites also paves the way for advances in the burgeoning field of flexible thermoelectrics. In this study, we demonstrate that the three-dimensional nanowire networks made of ferromagnetic metals maintain the intrinsic bulk thermoelectric power of their bulk constituent even for a diameter reduced to approximately 23 nm. Furthermore, we showcase the pioneering magneto-thermoelectric measurements of three-dimensional interconnected nickel nanotube networks. These macroscopic materials, comprising interconnected nanotubes, enable the development of large-area devices that exhibit efficient thermoelectric performance, while their nanoscale tubular structures provide distinctive magneto-transport properties. This research represents a significant step toward harnessing the potential of macroscopic nanostructured materials in the field of thermoelectrics.

Epitaxial growth and magnetic properties of kagome metal FeSn/elemental ferromagnet heterostructures

Binary kagome compounds TmXn (T = Mn, Fe, Co; X = Sn, Ge; m:n = 3:1, 3:2, 1:1) have garnered recent interest owing to the presence of both topological band crossings and flatbands arising from the geometry of the metal-site kagome lattice. To exploit these electronic features for potential applications in spintronics, the growth of high-quality heterostructures is required. Here, we report the synthesis of Fe/FeSn and Co/FeSn bilayers on Al2O3 substrates using molecular beam epitaxy to realize heterointerfaces between elemental ferromagnetic metals and antiferromagnetic kagome metals. Structural characterization using high-resolution x-ray diffraction, reflection high-energy electron diffraction, and electron microscopy reveals that the FeSn films are flat and epitaxial. Rutherford backscattering spectroscopy was used to confirm the stoichiometric window where the FeSn phase is stabilized, while transport and magnetometry measurements were conducted to verify metallicity and magnetic ordering in the films. Exchange bias was observed, confirming the presence of antiferromagnetic order in the FeSn layers, paving the way for future studies of magnetism in kagome heterostructures and potential integration of these materials into devices.

Strain‐controlled dynamics of transverse domain walls in hybrid piezoelectric–magnetostrictive heterostructures: An asymptotic approach

AbstractThe present work deals with an analytical study of the statical and dynamical behavior of transverse magnetic domain walls in hybrid bilayer piezoelectric/magnetostrictive heterostructures under the combined influence of spin‐polarized electric currents, transverse, and axial applied magnetic fields. The magnetostrictive material is considered to be isotropic and linearly elastic. We perform the investigation within the framework of the one‐dimensional Landau–Lifshitz–Gilbert equation. By employing the regular perturbation asymptotic expansion approach, we derive the explicit analytical expression of the most significant dynamic features, namely, traveling wave profile, DW velocity, and displacement under the influence of small and moderate transverse magnetic fields. Finally, we illustrate numerically the analytical results and delineate the domain wall motion for metallic and semiconductor ferromagnets.

GdFe-based nanostructured thin films with large perpendicular magnetic anisotropy for spintronic applications

In this study, we investigated the impact of geometric factors on the magnetic anisotropy of Gd-Fe alloy thin films deposited on nanoporous alumina membranes. By synthesizing Gd-Fe alloy nanostructure thin films with different hole diameters (ranging from 45 to 90 nm) and keeping the layer thickness and lattice parameters fixed at 45 nm and 105 nm, respectively, we observed a significant perpendicular magnetic anisotropy (PMA) in samples with hole diameter above 65 nm. The transition from in-plane to out-of-plane magnetization in Gd-Fe alloy nanostructure thin films occurred at a critical antidot hole diameter of 75 nm. The observed variations in coercivity and remanence with the nanohole diameter are attributed to substantial changes in the magnetization mechanisms induced by the nanoholes. This novel induction of PMA in Gd-Fe alloy nanostructure thin films through the manipulation of geometric parameters in the antidot arrays opens new possibilities for tailoring the magnetic behavior of ferromagnetic metals with pronounced PMA.

Strain-restricted transfer of ferromagnetic electrodes for constructing reproducibly superior-quality spintronic devices

Spintronic device is the fundamental platform for spin-related academic and practical studies. However, conventional techniques with energetic deposition or boorish transfer of ferromagnetic metal inevitably introduce uncontrollable damage and undesired contamination in various spin-transport-channel materials, leading to partially attenuated and widely distributed spintronic device performances. These issues will eventually confuse the conclusions of academic studies and limit the practical applications of spintronics. Here we propose a polymer-assistant strain-restricted transfer technique that allows perfectly transferring the pre-patterned ferromagnetic electrodes onto channel materials without any damage and change on the properties of magnetism, interface, and channel. This technique is found productive for pursuing superior-quality spintronic devices with high controllability and reproducibility. It can also apply to various-kind (organic, inorganic, organic-inorganic hybrid, or carbon-based) and diverse-morphology (smooth, rough, even discontinuous) channel materials. This technique can be very useful for reliable device construction and will facilitate the technological transition of spintronic study.