In-plane Magnetic Field Research Articles

Orbital Magneto-Nonlinear Anomalous Hall Effect in Kagome Magnet Fe_{3}Sn_{2}.

It has been theoretically predicted that perturbation of the Berry curvature by electromagnetic fields gives rise to intrinsic nonlinear anomalous Hall effects that are independent of scattering. Two types of nonlinear anomalous Hall effects are expected. The electric nonlinear Hall effect has recently begun to receive attention, while very few studies are concerned with the magneto-nonlinear Hall effect. Here, we combine experiment and first-principles calculations to show that the kagome ferromagnet Fe_{3}Sn_{2} displays such a magneto-nonlinear Hall effect. By systematic field angular and temperature-dependent transport measurements, we unambiguously identify a large anomalous Hall current that is linear in both applied in-plane electric and magnetic fields, utilizing a unique in-plane configuration. We clarify its dominant orbital origin and connect it to the magneto-nonlinear Hall effect. The effect is governed by the intrinsic quantum geometric properties of Bloch electrons. Our results demonstrate the significance of the quantum geometry of electron wave functions from the orbital degree of freedom and open up a new direction in Hall transport effects.

An in-situ magnetising holder achieving 1.5 T in-plane field in 200 kV transmission electron microscope

A strong in-plane magnetic field is required for Lorentz transmission electron microscopy (LTEM) to observe the evolution of the magnetic domain structure of materials with high coercivity, particularly for research on rare-earth permanent magnets. However, the maximum field of the present in-situ magnetising holder applied in 200-kV or 300-kV TEM does not exceed 0.1 T. In this study, the reason for the low field was analysed, and the field strength was significantly elevated by reducing the field application area of the field generator. From finite element method calculations and experimental measurements, a 1.5 T in-plane field was achieved by our new holder in a 200-kV TEM, and images with good quality could still be obtained. Using the newly developed holder, the magnetisation process of hot-pressed NdFeB magnets was observed. The in-situ magnetising holder can be used in research on a wide variety of magnetic materials.

Estimation of the interfacial Dzyaloshinskii–Moriya interaction in all-metallic multilayer with perpendicular magnetic anisotropy

The interfacial Dzyaloshinskii–Moriya (iDMI) interaction which arises at the interface between a heavy metal (HM) and a ferromagnet (FM) can stabilize chiral Néel type domain walls in ultrathin perpendicularly magnetized multilayers. Dissimilar HMs are required on both bottom and top sides of the FM layer in order to introduce the structural inversion asymmetry which ensures an effective iDMI in the FM layer. HMs like Pt, Ir, Ta etc are very well known for developing large iDMI in the interface with Co, whereas noble metals like Au can produce negligible iDMI. Therefore, a multilayer Pt/Co/Au is chosen to determine the individual iDMI in the Pt/Co interface. Some procedures like field-induced domain wall motion study, spin–orbit torque efficiency estimation study are well established to quantify the effective field due to the iDMI ( HDMI ) which in turn gives the strength of the iDMI ( Deff ). Besides these procedures, a current-induced switching of magnetization was studied to construct a switching phase diagram where the critical current density of magnetization switching has been plotted as a function of the applied in-plane magnetic field. The experimentally constructed diagram and the simulated diagram using a micromagnetic study have revealed the possibility to quantify HDMI . Thus, a systematic and unified estimation of Deff has been done on all-metallic Ta/Pt/Co/Au multilayers.

Field-Free Switching of Perpendicular Magnetization in an Ultrathin Epitaxial Magnetic Insulator.

For energy-efficient magnetic memories, switching of perpendicular magnetization by spin-orbit torque (SOT) appears to be a promising solution. This SOT switching requires the assistance of an in-plane magnetic field to break the symmetry. Here, we demonstrate the field-free SOT switching of a perpendicularly magnetized thulium iron garnet (Tm3Fe5O12, TmIG). The polarity of the switching loops, clockwise or counterclockwise, is determined by the direction of the initial current pulses, in contrast with field-assisted switching where the polarity is controlled by the direction of the magnetic field. From Brillouin light scattering, we determined the Dzyaloshinskii-Moriya interaction (DMI) induced by the Pt-TmIG interface. We will discuss the possible origins of field-free switching and the roles of the interfacial DMI and cubic magnetic anisotropy of TmIG. This discussion is substantiated by magnetotransport, Kerr microscopy, and micromagnetic simulations. Our observation of field-free electrical switching of a magnetic insulator is an important milestone for low-power spintronic devices.

An ideal candidate for observing anomalous Hall effect induced by the in-plane magnetic field

The anomalous Hall effect induced by the in-plane magnetic field (anomalous planar Hall effect) has recently attracted a lot of interests due to its numerous advantages. Although several schemes have been put forward in theory, experimental observations in many materials so far are often accompanied by planar Hall effects due to other mechanisms, rather than the pure anomalous planar Hall effect (APHE). We propose the surface state of the strained topological insulator as an ideal candidate to observe this effect. The surface state exhibits a pure APHE, characterized by a linear dependence on the magnetic field and a 2π periodicity, which remains robust against the scattering of non-magnetic and various magnetic impurities, as long as the uniaxial strain preserves mirror symmetry. Although a general strain that breaks the mirror symmetry can induce the conventional Drude Hall effect, the anomalous contribution remains dominant. Furthermore, we present a feasible scheme to distinguish between the two contributions based on their distinct magnetic field dependencies. Our work is of great significance for promoting experimental observation of the APHE and provides reference value in the search for other realistic materials.

Parallel pumping of magnons in inhomogeneous spin textures probed through NV spin relaxometry

We combine micromagnetic simulations and nitrogen-vacancy (NV) defect center spin relaxometry measurements to study magnon modes in inhomogeneous spin textures. A thin, micrometer-scale ferromagnetic disk is magnetized in a vortex state in which the magnetization curls around a central core. Micromagnetic simulations show that at zero applied field, the magnetization dynamics of the disk consist of a low frequency gyrotropic mode and higher frequency azimuthal magnon modes, all far detuned from the NV spin transition frequencies. An in-plane static magnetic field breaks the azimuthal symmetry of the vortex state, resulting in the magnon modes transforming in frequency and spatial profile as the field increases. Experimentally, we probe the dynamics of vortex magnetization as a function of applied in-plane static field and ac driving frequency by optically monitoring a nearby NV defect center spin. At certain values of the applied magnetic field, we observe enhanced spin relaxation when driving at twice the frequency of the NV ground state spin transition in optically detected magnetic resonance measurements. We attribute this effect to parallel pumping of a magnon mode in the disk producing magnons at half the excitation frequency. Micromagnetic simulations support this finding, showing spatial and spectral overlap of a confined magnon mode and an NV spin transition, with sufficient interaction strength to explain the observed signal.

Manipulation of the magnetic monopole injection for topological transition

Manipulating the topological properties of spin textures in magnetic materials is of great interest due to the rich physics and promising technological applications of these materials in advanced electronic devices. A spin texture with desired topological properties can be created by magnetic monopole injection, resulting in topological transitions involving changes in the topological charge. Therefore, controlling magnetic monopole injection has paramount importance for obtaining the desired spin textures but has not yet been reported. Here, we report the use of reliably manipulated magnetic monopole injection in the topological transition from stripe domains to skyrmions in an Fe/Gd multilayer. An easily tunable in-plane magnetic field applied to an Fe/Gd multilayer plays a key role in the magnetic monopole injection by modulating the local exchange energy. Our findings facilitate the efficient management of topological transitions by providing an important method for controlling magnetic monopole injection.

Stable skyrmions in Co/Ni-based nanopillars with perpendicular magnetization anisotropy

Micromagnetic simulations have been conducted to explore the formation rules of stable skyrmions in Co/Ni-based perpendicular magnetization anisotropy nanopillars with Dzyaloshinskii–Moriya Interaction (DMI). The results show that an appropriate perpendicular magnetic field can generate a robust Néel-type skyrmion magnetic configuration in the free layer with a 5° tilted easy axis. The creation and stability of skyrmion states also depends on the strength of the DMI and the size of nano-disk. Furthermore, we observed intriguing behavior in the case of the free layer with a perfectly perpendicular easy axis. Skyrmion states appeared in two distinct regions of perpendicular magnetic field when both perpendicular and in-plane magnetic fields were applied. This discontinuity arises from the nucleation of initial Bloch-type skyrmions. These results contribute to comprehending the formation mechanism of stable skyrmions in perpendicular magnetic anisotropy multilayers and may promote the development of skyrmion-based nanodevices.

Orbital Origin of the Intrinsic Planar Hall Effect.

Recent experiments reported an antisymmetric planar Hall effect, where the Hall current is odd in the in plane magnetic field and scales linearly with both electric and magnetic fields applied. Existing theories rely exclusively on a spin origin, which requires spin-orbit coupling to take effect. Here, we develop a general theory for the intrinsic planar Hall effect (IPHE), highlighting a previously unknown orbital mechanism and connecting it to a band geometric quantity-the anomalous orbital polarizability (AOP). Importantly, the orbital mechanism does not request spin-orbit coupling, so sizable IPHE can occur and is dominated by an orbital contribution in systems with weak spin-orbit coupling. Combined with first-principles calculations, we demonstrate our theory with quantitative evaluation for bulk materials TaSb_{2}, NbAs_{2}, and SrAs_{3}. We further show that AOP and its associated orbital IPHE can be greatly enhanced at topological band crossings, offering a new way to probe topological materials.

Wall-attached convection under strong inclined magnetic fields

We employ a linear stability analysis and direct numerical simulations to study the characteristics of wall modes in thermal convection in a rectangular box under strong and inclined magnetic fields. The walls of the convection cell are electrically insulated. The stability analysis assumes periodicity in the spanwise direction perpendicular to the plane of a homogeneous magnetic field. Our study shows that for a fixed vertical magnetic field, the imposition of horizontal magnetic fields results in an increase of the critical Rayleigh number along with a decrease in the wavelength of the wall modes. The wall modes become tilted along the direction of the resulting magnetic fields and therefore extend further into the bulk as the horizontal magnetic field is increased. Once the modes localized on the opposite walls interact, the critical Rayleigh number decreases again and eventually drops below the value for onset with a purely vertical field. We find that for sufficiently strong horizontal magnetic fields, the steady wall modes occupy the entire bulk and therefore convection is no longer restricted to the sidewalls. The aforementioned results are confirmed by direct numerical simulations of the nonlinear evolution of magnetoconvection. The direct numerical simulation results also reveal that at least for large values of horizontal magnetic field, the wall-mode structures and the resulting heat transfer are dependent on the initial conditions.

Enhancing magnetically driven microswimmer velocity via low Reynolds number hydrodynamic interactions

The motion of comoving magnetic microswimmers is modeled by considering the inter-hydrodynamic interactions (HI) under low Reynolds number conditions. The microswimmer is a two-link design consisting of a magnetic head attached to a slender tail via a torsional spring, and it is driven by an external planar oscillatory magnetic field. The inter-HI considered are the head-head and tail-tail interactions. The propulsion velocity for the comoving mode is calculated and compared with that of an isolated mode. The comparative results show that the comoving mode velocity can be either similar or greater than the isolated mode, depending on the actuation frequency. The parametric dependency results show that the velocity generated in comoving mode depends on the average separation distance and length-to-width ratio of the tail. For proof of concept, a low-cost fabrication protocol is implemented to design a millimeter-sized magnetic flagellated swimmer. The experimental result shows that the comoving swimming mode generates larger velocity in comparison to isolated swimming.

Thermal Stability of Skyrmion Tubes in Nanostructured Cuboids.

Magnetic skyrmions in bulk materials are typically regarded as two-dimensional structures. However, they also exhibit three-dimensional configurations, known as skyrmion tubes, that elongate and extend in-depth. Understanding the configurations and stabilization mechanism of skyrmion tubes is crucial for the development of advanced spintronic devices. However, the generation and annihilation of skyrmion tubes in confined geometries are still rarely reported. Here, we present direct imaging of skyrmion tubes in nanostructured cuboids of a chiral magnet FeGe using Lorentz transmission electron microscopy (TEM), while applying an in-plane magnetic field. It is observed that skyrmion tubes stabilize in a narrow field-temperature region near the Curie temperature (Tc). Through a field cooling process, metastable skyrmion tubes can exist in a larger region of the field-temperature diagram. Combining these experimental findings with micromagnetic simulations, we attribute these phenomena to energy differences and thermal fluctuations. Our results could promote topological spintronic devices based on skyrmion tubes.

Two-fold symmetric superconductivity in the Kagome superconductor RbV3Sb5

The recently discovered kagome superconductors offer a promising platform for investigating intertwined orders and novel states, including topology, superconductivity, charge density waves, and more. The interplay among these orders can spontaneously break rotational symmetry, giving rise to exotic phenomena such as nematicity or even nematic superconductivity. Here we present our findings on the two-fold symmetric superconductivity in thin-flake RbV3Sb5 in response to direction-dependent in-plane magnetic fields, in contrast to the inherent six-fold structural symmetry of the crystal lattice. The two-fold symmetry was evidenced through a combination of magnetoresistance transport experiments, critical magnetic field measurements, and observations of anisotropic superconducting gaps. Additionally, by altering the experimental configuration, we also detected the presence of six-fold symmetric components superimposed on the two-fold symmetry at the boundary between normal and superconducting states. Our results underscore the correlation-driven symmetry-breaking phenomena and emphasize the potential of this correlated kagome family as a promising platform for investigating intertwined orders, including unconventional superconductivity.

The phase diagram of the baxter-Wu model in the magnetic field and temperature plane

Using the Fisher zeros of the partition function of a finite sized cluster with ‘spherical’ boundary conditions an approximate phase diagram in the magnetic field—temperature plane is obtained for the Baxter-Wu model. The phase diagram compares favourably with previous approximations as well as the known exact results when the magnetic field is zero. The accuracy of the approximated phase diagram, especially for small values of the magnetic field, is dependent on the fact, as shown previously, that for zero magnetic field the Fisher zeros for this cluster lie on loci giving the exact zero field critical temperature.

Bloch oscillations probed quantum phases in HgTe quantum wells

The semiconductor quantum well based on mercury telluride is characterized by two distinct phases: conventional insulating phase and topological insulating phase with helical edge states. The system undergoes a topological quantum phase transition from one phase to the other, tuned by the critical geometric parameters of the quantum well. It is shown that the quantum states in each phase exhibit distinct flavors of Bloch oscillations, depending strongly on the geometric parameters and crystal momentum of the system. In particular, the group and Berry velocities and the real-space trajectories exhibit pronounced Bloch oscillations. Interestingly, the x- and y-components of the group velocity are interchanged by interchanging their corresponding components of the crystal momentum. In addition, a Gaussian wave packet undergoes distinct time evolution in each quantum phase of the HgTe quantum well. Moreover, the effects of applied in-plane electric and transverse magnetic fields are determined within the framework of Newtonian mechanics, leading to the geometric visualization of such an oscillatory motion. We find that in the presence of both applied in-plane electric and transverse magnetic fields simultaneously, the system undergoes a dynamic phase transition between confined and de-confined states, tuned by the relative strength of the fields. It is argued that the distinct Bloch oscillations originate from the peculiar band structure of HgTe quantum wells in each quantum phase. Furthermore, we find that the direct-current drift velocity in each quantum phase exhibits negative differential conductivity, a hallmark of the Bloch oscillation regime.

Maximum Aligned Directional Derivative (MADD) Technique for Planar Structure Analysis in Space

Interplanetary discontinuities are the most common intermittent structures in the solar winds, whose jump conditions conform to the Rankine–Hugoniot relations. The identification and analysis of such planar structures rely on an accurate determination of the normal vectors. In this study, we perform a benchmark test of a technique designed to estimate the dimensionality and orientation of the magnetic fields based on four spacecraft measurements. Such a technique operates on the fact that in a strictly planar magnetic field, three columns of ∇ B are all aligned and the characteristic direction corresponding to the maximum aligned directional derivative (MADD; i.e., the maximum of ∣∇B·r^∣ ) can be considered the normal vector of the structure. A benchmark test of this technique, using both the simulation data and numerical models of planar structures, shows that the MADD technique can identify planar magnetic field structures efficiently. For a discontinuity with translational and rotational motion, MADD is able to estimate its normal vector with second-order precision and the speed of motion with first-order precision. Two demonstrations of the MADD application to the tangential discontinuity and shock structures are presented to show its efficiency and superiority. In principle, MADD is suitable for all types of planar structures in space. Compared with the minimum variance analysis and timing techniques, MADD is superior in the study of intermediate shocks that exhibit magnetic coplanarity and rapid spatial evolution.

Magnitno-silovaya i nelineyno-opticheskaya mikroskopiya pripoverkhnostnoy domennoy struktury epitaksial'noy plenki ferrita-granata

The magnetic properties of the surface layer of an epitaxial bismuth-doped iron garnet film with a weak uniaxial anisotropy are studied by magnetic force, optical, and nonlinear optical microscopy. A significant modulation of optical second harmonic generation intensity along stripe domains is detected near the free film surface. This modulation is caused by periodic distortions of the stripe domain structure near the film surface and the presence of surface closure domains detected by magnetic force microscopy (MFM). A series of MFM images of the film taken in an in-plane magnetic field varying from –400 to 400 Oe demonstrates quasi-static nucleation of closure domains periodically located along stripe domains.

Parametric mechanism of the magnetization reversal as a low-power recording mechanism for MRAM. Measurement of spin-accumulation-induced in-plane magnetic field in a FeB nanomagnet

The parametric torque presents a promising recording mechanism for MRAM, complementing Spin Transfer Torque and Spin Orbit Torque, enabling magnetization reversal in a nanomagnet using a DC electrical current. Its resonance nature allows for optimization of magnetization reversal at a lower current, presenting an opportunity for a lower recording current and, therefore, for efficient and high-performance operation in modern MRAM technology. The in-plane magnetic field generated by spin accumulation serves as the driving force behind this torque. Experimental measurements of the current-induced in-plane magnetic field in the FeB nanomagnet reveal its magnitude to be around 40 Gauss at a current density of 25 mA/μm2, a value adequate for facilitating parametric magnetization reversal. The parametric torque is analytically calculated by solving the Landau–Lifshitz equation. Analytical calculations demonstrate its potential in advancing modern MRAM technology.

Control of valley optical conductivity and topological phases in buckled hexagonal lattice by orientation of in-plane magnetic field

We investigate the optical conductivity, along with longitudinal and transverse conductivities, in buckled hexagonal lattice such as silicene subjected to both an in-plane magnetic field and a perpendicular electric field. In this model, we neglect the effect of the spin-orbit interaction, which is of a smaller order compared to the strong staggered potential and the next-nearest hoping energy. The orientations of the in-plane magnetic field and the perpendicular electric field give rise to a non-uniform, tunable gap. The Chern number for each valley degree of freedom deviates from being constant but remains steady when summed over the entire Brillouin zone. The longitudinal and transverse currents, in the case of a specific valley, can be selected by adjusting the direction of the electric field in the semimetal phase. Furthermore, the defining characteristics of topological phases induces the rapid change in longitudinal conductivity when varying the angle of orientation of the in-plane magnetic field under monochromatic light, and perfect valley filtering in transverse conductivity. The transverse current associated with a specific valley can be selected when the angle of orientation satisfies the specific conditions. This investigation paves the way for materials design with valley-locked current, using a specific orientation of the in-plane magnetic field.

Spectral properties of disordered Ising superconductors with singlet and triplet pairing in in-plane magnetic fields

Spectral properties of disordered Ising superconductors with singlet and triplet pairing in in-plane magnetic fields