Nonmagnetic Metal Research Articles

Impact of interfacial chemical state on spin pumping and inverse spin Hall effect in YIG/Pt hybrids

The interface between ferromagnetic (FM) and nonmagnetic (NM) metal plays a fundamental role in the generation, transmission, detection of spin current, and spin-based devices. The impact of physical properties on the interface such as roughness, crystallization conditions, and even impedance matching has been widely investigated. In this work, the effects of interfacial chemical state at the interface of ${\mathrm{Y}}_{3}{\mathrm{Fe}}_{5}{\mathrm{O}}_{12}$ and Pt (YIG/Pt) are systematically investigated through spin injection. Prior to Pt deposition, the spin mixing conductance and inverse spin Hall voltage of YIG/Pt hybrids increased up to 300%, using surface chemical processing on YIG. The interfacial chemical state is identified from x-ray photoelectron spectroscopy spectra and peak decomposition. Both ${\mathrm{Fe}}^{2+}$ and ${\mathrm{Fe}}^{3+}$ cations appear at the interface and higher content of ${\mathrm{Fe}}^{3+}$ enhances the interface magnetic moment which consequently plays a crucial role in spin injection efficiency and inverse spin Hall voltage. In order to prevent the influence of magnetic proximity effect of Pt layers close to the FM/NM interface, a Cu spacer is inserted. It is found that the improved spin injection efficiency due to iron cations still exists in the YIG/Cu/Pt structure, which confirms the universal influence of the interfacial chemical state on spin pumping efficiency. This discovery has potential implications for spin generation, detection, and even optimization of spintronic devices.

Electronic and magnetic properties of 3d transition metal atom adsorbed Zr2CO2 Mxene: First-principles study

The structural, electronic and magnetic properties of the 3d transition metal (TM) atoms (from Sc to Zn) adsorbed Zr2CO2 Mxenes were investigated systematically by using first-principles calculations. The adsorption energies demonstrate that all the TM atoms are chemically adsorbed above the C atom (TC) sites of the Zr2CO2 Mxenes except for the Zn atom. Furthermore, the analyses of bond length, charge transfer and vDW interaction ratio demonstrate that the interaction between adatoms (from Sc to Cu) and under-coordinated atoms is mainly covalent bonding features. Cu adsorbed Zr2CO2 Mxene exhibits nonmagnetic metal, and Ni and Zn adsorbed systems show nonmagnetic semiconductor. While Sc, V, Cr, Mn and Co adsorbed Zr2CO2 Mxenes exhibit magnetic metal. Interestingly, the Fe adsorbed system shows bipolar magnetic semiconductor character. Especially, the Ti adsorbed system exhibits half-metallic character. Our results demonstrate that the 3d TM atom adsorbed Zr2CO2 Mxene could provide various potential application in nanoelectronics and spintronics.

Meronlike Spin Textures in In-Plane-Magnetized Thin Films

The interfacing of magnetic materials with nonmagnetic heavy metals with a large spin-orbit coupling, such as $\mathrm{Pt}$, results in an asymmetric exchange interaction at the interface due to the Dzyaloshinskii-Moriya interaction (DMI), which in turn leads to the formation of skyrmions and topological spin structures in perpendicularly magnetized multilayers. Here, we show that out-of-plane spin domains with lateral dimensions from 200 nm to 2 $\ensuremath{\mu}\mathrm{m}$ are stabilized in in-plane magnetized $\mathrm{Ta}$/$\mathrm{Co}$/$\mathrm{Pt}$ trilayers. We show that these spin textures are largely insensitive to the direction of the in-plane magnetization switched by either magnetic fields or electric fields applied across a ${\mathrm{Si}}_{3}{\mathrm{N}}_{4}$ gate dielectric. The results of micromagnetic simulations indicate that the DMI is required for the stabilization of such out-of-plane domains and that the presence of surface roughness helps to stabilize larger structures, in agreement with experimental results. We identify these spin structures as meronlike topological textures, characterized by a perpendicular spin texture in an uniformly in-plane magnetized system.

Orbital gyrotropic magnetoelectric effect and its strain engineering in monolayer NbX2

Electrical control of the orbital degrees of freedom is an important area of research in the emerging field of "orbitronics." Orbital {\it gyrotropic} magneto-electric effect (OGME) is the generation of an orbital magnetization in a nonmagnetic metal by an applied electric field. Here, we show that strain induces a large GME in the monolayer Nb$X_2$ ($X =$ S, Se) normal to the plane, primarily driven by the orbital moments of the Bloch bands as opposed to the conventional spin magnetization, without any need for spin-orbit coupling. The key physics is captured within an effective two-band valley-orbital model and it is shown to be driven by three key ingredients: the intrinsic valley orbital moment, broken $C_{3z}$ symmetry, and strain-induced Fermi surface changes. The effect can be furthermore switched by changing the strain condition, with potential for future device applications.

Огромное магнетосопротивление в структуре металл--органический полупроводник--металл

The article represents results of huge magnetoresistance effect investigation in the structure of magnetic metal / organic semiconductor / nonmagnetic metal with magnitude of ~ 2600%. There are observed influence of magnetic field on concentration and mobility of charge carriers and on magnitude of ferromagnetic/semiconductor potential barrier. Theoretical interpretation is considered with previously discussed model. The model describes influence of hyperfine fields on spin selective hopping rate between the sites in the polymer

Highly nonlinear frequency-dependent spin-wave resonance excited via spin-vorticity coupling

A nonuniform vorticity of lattice deformation in a surface acoustic wave (SAW) can generate a spin current (SC) in nonmagnetic metals via spin-vorticity coupling (SVC). We demonstrated a strong enhancement of SVC-derived SC generated in Cu and Pt films with increasing the frequency of the SAW by observing the spin-wave resonance (SWR) in an adjacent NiFe film. The comparative amplitudes and high-order frequency variations of SWR in NiFe/Cu and NiFe/Pt bilayers imply that the amplitude of the SC generated via SVC in a SAW is robust against the strength of spin-orbit interaction in nonmagnetic metals.

Hydrogen tunes magnetic anisotropy by affecting local hybridization at the interface of a ferromagnet with nonmagnetic metals

Ionic control of magnetic properties, dubbed magneto-ionics, has gained much attention in recent years due to the sizable effects that can be induced by electrically controlled ion motion. Here we assess the mechanism by which hydrogen affects magnetic anisotropy in representative ferromagnetic/nonmagnetic metal layers. We take Co/Pd film as a model system that is widely used in spintronics. First-principles calculations demonstrate that the magnetic moment can be switched by ${90}^{\ensuremath{\circ}}$ via hydrogen insertion at the Co/Pd interface. This control results from hydrogen-induced changes in magnetic anisotropy originating from modifications to the electronic structure. Accumulation of hydrogen at the Co/Pd interface affects the hybridization between neighboring Co and Pd layers, leading to a decrease of the perpendicular anisotropy component, and eventually changes the net magnetic anisotropy to in-plane. Hydrogen penetration into the interior Co layers has the opposite effect, promoting perpendicular magnetic anisotropy. These changes are governed by competing contributions of the ${d}_{xy};$ ${d}_{{x}^{2}+{y}^{2}}$ and the $3{d}_{{z}^{2}};$ $3{d}_{zy}$ states, which are mainly responsible for the perpendicular and the in-plane magnetocrystalline anisotropy, respectively. By using this understanding, we predict that hydrogen accumulation at Fe/V interfacial layers causes the opposite spin reorientation effect, promoting perpendicular magnetic anisotropy.

Spin\u2013orbit torque nano-oscillator with giant magnetoresistance readout

Spin-orbit torque nano-oscillators based on bilayers of ferromagnetic and nonmagnetic metals are ultra-compact current-controlled microwave signal sources. They are attractive for practical applications such as microwave assisted magnetic recording, neuromorphic computing, and chip-to-chip wireless communications. However, a major drawback of these devices is low output microwave power arising from the relatively small anisotropic magnetoresistance of the ferromagnetic layer. Here we experimentally show that the output power of a spin-orbit torque nano-oscillator can be significantly enhanced without compromising its structural simplicity. Addition of a ferromagnetic reference layer to the oscillator allows us to employ current-in-plane giant magnetoresistance to boost the output power of the device. This enhancement of the output power is a result of both large magnitude of giant magnetoresistance compared to that of anisotropic magnetoresistance and their different angular dependencies. Our results hold promise for practical applications of spin-orbit torque nano-oscillators.

Spin Caloritronics in 3D Interconnected Nanowire Networks.

Recently, interconnected nanowire networks have been found suitable as flexible macroscopic spin caloritronic devices. The 3D nanowire networks are fabricated by direct electrodeposition in track-etched polymer templates with crossed nano-channels. This technique allows the fabrication of crossed nanowires consisting of both homogeneous ferromagnetic metals and multilayer stack with successive layers of ferromagnetic and non-magnetic metals, with controlled morphology and material composition. The networks exhibit extremely high, magnetically modulated thermoelectric power factors. Moreover, large spin-dependent Seebeck coefficients were directly extracted from experimental measurements on multilayer nanowire networks. This work provides a simple and cost-effective way to fabricate large-scale flexible and shapeable thermoelectric devices exploiting the spin degree of freedom.

Combining Spin-Seebeck and Nernst Effects in Aligned MnBi/Bi Composites.

The spin-Seebeck effect (SSE) is an advective transport process traditionally studied in bilayers composed of a ferromagnet (FM) and a non-magnetic metal (NM) with strong spin-orbit coupling. In a temperature gradient, the flux of magnons in the FM transfers spin-angular momentum to electrons in the NM, which by the inverse spin-Hall effect generates an SSE voltage. In contrast, the Nernst effect is a bulk transport phenomenon in homogeneous NMs or FMs. These effects share the same geometry, and we show here that they can be added to each other in a new combination of FM/NM composites where synthesis via in-field annealing results in the FM material (MnBi) forming aligned needles inside an NM matrix with strong spin-orbit coupling (SOC) (Bi). Through examination of the materials’ microstructural, magnetic, and transport properties, we searched for signs of enhanced transverse thermopower facilitated by an SSE contribution from MnBi adding to the Nernst effect in Bi. Our results indicate that these two signals are additive in samples with lower MnBi concentrations, suggesting a new way forward in the study of SSE composite materials.

INFLUENCE OF WINDING ENDS ON THE PARAMETERS OF PULSE INDUCTOR WITH U-SHAPED CORE

It is known from the scientific literature that magnetic pulse processing of electrically conductive non-magnetic sheet materials helps to reduce residual stresses, especially in welded joints. This is due to magnetoplastic and electroplastic effects. To create such effects in non-magnetic electrically conductive materials with welded joints, an inductor with pulsed magnetic field, U-shaped magnetic circuit and hollow conductor for possibility of active cooling of the winding is proposed. Such inductor allows inducing high-density pulsed currents in electrically conductive non-magnetic sheet materials with welded joints. It studies the parameters of the inductor - active resistance and inductance in the frequency-domain mode. The parameters calculated in two-dimensional and three-dimensional models are compared. The electromagnetic field is calculated using Maxwell equations and finite element method. Parameters of an ends of winding are determined by the difference in the parameters of the three-dimensional and two-dimensional models of the induction system. Resistance is calculated separately in the groove`s part of the winding, the outer part and on the frontal parts. The parameters of the induction system with a ferromagnetic core and non-magnetic thin-sheet alloy AMg6 are calculated for various values of complex amplitude of current in winding. Additionally, the parameters are calculated both without the magnetic core and without the non-magnetic metal. The quantitative comparison of the parameters of the three-dimensional model with the two-dimensional one is performed. The active resistance and inductance of end parts of the inductor are investigated by well-known analytical expressions from handbooks of electric machines. References 11, figures 3, tables 6.

Monolayer Mo2B: A non-magnetic metal and potential application as anode material for ion batteries and catalyst for hydrogen evolution

Using the first principle method, the properties and electronic structures for two dimensional (2D) Mo2B are studied. Our investigations show 2D Mo2B with the hexagonal structure is a stable phase. Electronic structure show that 2D Mo2B is a typical metal and non-magnetic. The native defects, as well as a few percent of biaxial tensions and compressions cannot destroy its metallic behaviors. Stable metallic properties suggest 2D Mo2B is a promising electrode material in ion batteries. For Li and Na adsorbed cases, negative adsorption energies suggest strong interactions between Li (Na) and 2D Mo2B, which could prevent the formation of metallic Li and Na, and improve ions batteries’ safety and reversibility when utilized as anodes in ion batteries. The diffusion barriers for Li (Na) ions on 2D Mo2B are 0.073 (0.069) eV, and the open circuit voltage for Li (Na) adsorbed are 0.62–1.15 (0.42–1.41) V. Such diffusion barriers and open circuit voltage indicate 2D Mo2B is a promising anode material for Li or Na ion batteries. Smaller Gibbs free energy implies 2D Mo2B have a good prospect as a catalyst for hydrogen evolution.

Microwave Magnon-Plasmon-Polaritons in the Ferromagnetic Metal–Screened Insulator Structure

A possibility for surface magnon–plasmon–polaritons (SMPPs)–coupled microwave oscillations of magnetization, electron density, and electromagnetic field–to exist in real ferromagnetic metal–insulator–ideal non-magnetic metal structures has been analyzed theoretically. The developed theory predicts that the effective formation of SMPPs is possible only at certain values of the external dc magnetic field and must be accompanied by a shift in the characteristic frequency of the resonance plasmon-polariton systems. A theoretical estimation of the frequency shift for SMPPs in the structure “surface electromagnetic wave resonator made of permalloy–vacuum–ideal metal” gives a value of ±45 MHz for a resonator with a characteristic frequency of 10 GHz, which seems sufficient for this effect to be observed experimentally.

Ferromagnetism in PtTe2 monolayer introduced by doping 3d transition metal atoms and group VA and VIIB atoms

Most of the two-dimensional layered materials discovered so far are intrinsically nonmagnetic. Introducing ferromagnetism into these materials will expand their application greatly in the field of spintronics. Here we study the introduction of ferromagnetism into the PtTe2 monolayer via doping the 3d transition metal atoms and the group VA and VIIB atoms by means of the first-principles calculations. Results show that the magnetic order can be introduced in the V-, Mn-, Fe-, Cu- and Zn-doped PtTe2 monolayers, among which the V-, Cu- and Zn-doped monolayers have ferromagnetic ground state, and the Mn- and Fe-doped monolayers have antiferromagnetic ordering in ground state. Among the group VA atom doped systems, N-, P- and As-doped monolayers exhibit ferromagnetic, and Sb doped monolayer is a nonmagnetic metal. All the VIIB atom doped PtTe2 monolayers are nonmagnetic, while the doping makes the PtTe2 monolayer transit from an indirect bandgap semiconductor to metal. The findings obtained in this work may initiate new experimental exploration and expand the application of the layered transition-metal ditellurides in spintronics.

Robust spin–orbit torques in ferromagnetic multilayers with weak bulk spin Hall effect

The spin currents generated by spin–orbit coupling in nonmagnetic metals or at interfaces with broken inversion symmetry are particularly important for devices with extraordinary performance. We have investigated the spin–orbit torques (SOTs) in Ru/Fe/HfO2 heterostructures with weak perpendicular magnetic anisotropy. Although the bulk spin Hall effect (SHE) of the Ru layer is smaller than that of Pt, Ta, or W, robust SOT-induced magnetization switching can also be realized. Through nonadiabatic harmonic measurements, the effective spin Hall angle in Ru/Fe/HfO2 heterostructures is calculated to be −0.045. We have explored the mechanisms of spin current generation, which could stem from the Ru/Fe interfaces other than the weak bulk SHE of Ru. Our results suggest the spin current generation mechanisms in ferromagnet/nonmagnetic metal heterostructures remain to be further explored.

Broken symmetries and the related interface-induced effects at Weyl-system TaAs in proximity of noble metals

Weyl semimetal TaAs, congenially accommodating the massless Weyl fermions, furnishes a platform to observe a spontaneous breaking of either the time-reversal or the inversion symmetry and the concurrent genesis of pairs of Weyl nodes with significant topological durability. Former experimental analysis, which reveals that the near-zero spin-polarization of bulk TaAs, experiences a boost in proximity of point-contacts of non-magnetic metals along with the associated tip-induced superconductivity, provides the impetus to study the large-area stacked interfaces of TaAs with noble metals like Au and Ag. The primary outcomes of the present work can be listed as follows: (1) First-principles calculations on the interfacial systems have manifested an increment of the interface-induced spin-polarization and contact-induced transport spin-polarization of TaAs in proximity of noble metals; (2) In contrast to the single interface, for vertically stacked cases, the broken inversion symmetry of the system introduces a z-directional band-dispersion, resulting in an energetically separated series of non-degenerate band crossings. The simultaneous presence of such band-crossings and spin-polarization indicated the coexistence of both broken time reversal and inversion symmetries for metal-semimetal stacked interfaces; (3) quantum transport calculations on different device geometries reveal the importance of contact geometry for spin-transport in TaAs devices. Lateral contacts are found to be more effective in obtaining a uniform spin transport and larger transport spin polarization; (4) the phonon dispersion behaviour of TaAs displays a closure of band-gap with the associated increase of phonon-density of states for the acoustic modes in proximity of lateral contacts of noble metals.

The amplitude-sensitive eddy current method for investigation of the plastically deformed metal zone beneath the indent obtained by ball indentation

The paper presents the analysis of the results of plastic deformation zones obtained by the ball indentation into the surface of a non-magnetic metal plate using the amplitude-sensitive eddy current method. Calculation and experimental methods were used in the research. A two-dimensional finite-element model of an eddy current probe installed above a local plastically deformed zone on the metal plate surface was developed. The finite-element modelling of the electromagnetic field of eddy currents induced in the aluminium plate during multi-frequency excitation was made. It is found that the amplitude-sensitive eddy current method is appropriate not only to estimate the plastic deformation zone propagation depth, but also to detect a zone with the maximum stress values beneath the indent (hydrostatic core zone). An experimental verification of the proposed model was done. The specific zones in the deformed metal beneath the indent were detected by the eddy current method and the hydrostatic core size was evaluated.

Fabrication of Cylindrical Magnetic Nanoparticles for Functionalization of Polyelectrolyte Microcapsules

A problem of fabrication of magnetic polymer capsules for targeted drug delivery is considered. Magnetic nanoparticles are used in the problem under study. A method for fabrication of such particles involving synthesis of layered nanowires with alternating layers of the specified magnetic metal and sacrificial layers of nonmagnetic metal is proposed. A method for template-assisted synthesis based on ac-potential electroplating of specified metals in the pores of track membranes is used to fabricate wires with a diameter of 100 nm with nickel layers of 400 and 200 nm. A method for the subsequent extraction of nickel fragments using selective etching (removal) of copper fragments is developed. Procedures that prevent aggregation of magnetic nanoparticles and penetration of the nanoparticles in the shells of polymer capsules are considered.

Experimental Research of Induction Heating in Inner Hollow of Cylindrical Solenoid

Purpose. Experimental determination of the dependence of the magnetic field strength distributions and the density of induced currents in the metal of the tubular blank from its position in the cylindrical inductor internal hallow. Methodology. The electrodynamic problem solution using mathematical apparatus for analytical calculations. To describe the processes that arise in the material under processing, expressions for fields and currents flowing in non-magnetic metals under the action of a multi-turn cylindrical solenoid that derived from the system of Maxwell's equations. Accepted mathematical assumptions and simplifications do not affect the correctness of the results. Carrying out an experiment to determine the intensity of the magnetic field in the solenoid inner hollow and the induced currents density on the surface of the nonmagnetic blank. Results. The obtained experimental distributions of the magnetic field strength and induced currents with the full blank placement in the cylindrical inductor hollow correspond to the analytical relations derived earlier and coincide with the fundamental physical concepts of the processes taking place in the system. When the billet is partially placed in the inner hollow of the inductor, there is a sudden increase in the tangential magnetic field strength component. In this case, an extremum is observed in the end zone of the billet. This is explained by the concentration of induced currents in this region, as well as on the cylindrical surface of the billet. Originality. The average induction heating speeds correspond to the calculated values for the materials of the processed samples used in the experiment, which indicates the effectiveness of using this processing technology in equal measure, both non-magnetic metals and magnetic. The practical value of the results consists in the possibility of estimating the qualitative indices of the concentration of induced currents and heat release in the end part of nonmagnetic cylindrical preforms with their partial overlapping by an inductor to perform heating operations.

Experimental Research of Induction Heating in Inner Hollow of Cylindrical Solenoid

Purpose. Experimental determination of the dependence of the magnetic field strength distributions and the density of induced currents in the metal of the tubular blank from its position in the cylindrical inductor internal hallow. Methodology. The electrodynamic problem solution using mathematical apparatus for analytical calculations. To describe the processes that arise in the material under processing, expressions for fields and currents flowing in non-magnetic metals under the action of a multi-turn cylindrical solenoid that derived from the system of Maxwell's equations. Accepted mathematical assumptions and simplifications do not affect the correctness of the results. Carrying out an experiment to determine the intensity of the magnetic field in the solenoid inner hollow and the induced currents density on the surface of the nonmagnetic blank. Results. The obtained experimental distributions of the magnetic field strength and induced currents with the full blank placement in the cylindrical inductor hollow correspond to the analytical relations derived earlier and coincide with the fundamental physical concepts of the processes taking place in the system. When the billet is partially placed in the inner hollow of the inductor, there is a sudden increase in the tangential magnetic field strength component. In this case, an extremum is observed in the end zone of the billet. This is explained by the concentration of induced currents in this region, as well as on the cylindrical surface of the billet. Originality. The average induction heating speeds correspond to the calculated values for the materials of the processed samples used in the experiment, which indicates the effectiveness of using this processing technology in equal measure, both non-magnetic metals and magnetic. The practical value of the results consists in the possibility of estimating the qualitative indices of the concentration of induced currents and heat release in the end part of nonmagnetic cylindrical preforms with their partial overlapping by an inductor to perform heating operations.