Application Of In-plane Magnetic Field Research Articles

Tunable room temperature magnetic skyrmions in centrosymmetric kagome magnet Mn4Ga2Sn

The successful realization of skyrmion-based spintronic devices depends on the easy manipulation of underlying magnetic interactions in the skyrmion-hosting materials. Although the mechanism of skyrmion formation in non-centrosymmetric magnets is comprehensively established, the stabilization process of different skyrmion-like magnetic textures in centrosymmetric magnets needs further investigation. Here, we utilize Lorentz transmission electron microscopy study to report the finding of a tunable skyrmion lattice up to room temperature in a centrosymmetric kagome ferromagnet Mn4Ga2Sn. We demonstrate that a controlled switching between the topological skyrmions and non-topological type-II magnetic bubbles can be realized at the optimal magnetic anisotropy. We find that the topological skyrmions are the energetically most stable magnetic objects in the centrosymmetric hexagonal magnets, whereas application of in-plane magnetic field stabilizes type-II magnetic bubbles as an excited state. The present study is a significant step towards understanding of the skyrmion stabilization mechanism in centrosymmetric materials for their future applications.

Spin and valley degrees of freedom in a bilayer graphene quantum point contact: Zeeman splitting and interaction effects

We present a study on the lifting of degeneracy of the size-quantized energy levels in an electrostatically defined quantum point contact in bilayer graphene by the application of in-plane magnetic fields. We observe a Zeeman spin splitting of the first three subbands, characterized by effective Land\'e $g$ factors that are enhanced by confinement and interactions. In the gate-voltage dependence of the conductance, a shoulderlike feature below the lowest subband appears, which we identify as a 0.7 anomaly stemming from the interaction-induced lifting of the band degeneracy. We employ a phenomenological model of the 0.7 anomaly to the gate-defined channel in bilayer graphene subject to in-plane magnetic field. Based on the qualitative theoretical predictions for the conductance evolution with increasing magnetic field, we conclude that the assumption of an effective spontaneous spin splitting is capable of describing our observations, while the valley degree of freedom remains degenerate.

Stimulated Nucleation of Skyrmions in a Centrosymmetric Magnet.

Understanding the dynamics of skyrmion nucleation and manipulation is important for applications in spintronic devices. In this contribution, the spin textures at magnetic domain-boundaries stimulated by application of in-plane magnetic fields in a centrosymmetric kagome ferromagnet, Fe3Sn2, with thickness gradient are investigated using Lorentz transmission electron microscopy. Switching of the in-plane magnetic field is shown to induce a reversible transformation from magnetic stripes to skyrmions, or vice versa, at the interface between differently oriented domains. Micromagnetic simulations combined with experiments reveal that the rotatable anisotropy and thickness dependence of the response to the external in-plane field are the critical factors for the skyrmion formation. In addition, it is shown that the helicity of skyrmions can also be controlled using this dynamic process. The results suggest that magnetic materials with rotatable anisotropy are potential skyrmionic systems and provides a different approach for nucleation and manipulation of skyrmions in spintronic devices.

Origin of the magnetic field enhancement of the spin signal in metallic nonlocal spin transport devices

The nonlocal spin valve (NLSV) enables unambiguous study of spin transport, owing to its ability to isolate pure spin currents. A key principle of NLSV operation is that the ``spin signal'' is invariant under application of in-plane magnetic fields (above the ferromagnetic contact saturation field). Yet, for certain ferromagnet/normal metal pairings in NLSVs, an unexpected field enhancement of the spin signal occurs, presenting a challenge that has, thus far, been difficult to resolve with existing models. By correlating the extracted spin transport parameters with material, temperature, and field dependencies, in this work we identify field quenching of magnetic impurity scattering as the origin of this effect, confirmed by excellent agreement between our results and field-dependent Kondo theory. In addition to addressing this long-standing mystery, our findings highlight a potential systematic underestimation of spin transport parameters. By identifying signature field and temperature dependencies, we provide here a relatively simple means to isolate and quantify this additional relaxation mechanism.

Twisted monolayer and bilayer graphene for vertical tunneling transistors

We prepare twist-controlled resonant tunneling transistors consisting of monolayer and Bernal bilayer graphene electrodes separated by a thin layer of hexagonal boron nitride. The resonant conditions are achieved by closely aligning the crystallographic orientation of graphene electrodes, which leads to momentum conservation for tunneling electrons at certain bias voltages. Under such conditions, negative differential conductance can be achieved. Application of in-plane magnetic field leads to electrons acquiring additional momentum during the tunneling process, which allows control over the resonant conditions.

High Landau levels of two-dimensional electrons near the topological transition caused by interplay of spin-orbit and Zeeman energy shifts

In the presence of spin-orbit coupling two branches of the energy spectrum of 2D electrons get shifted in the momentum space. Application of in-plane magnetic field causes the splitting of the branches in energy. When both, spin-orbit coupling and Zeeman splitting are present, the branches of energy spectrum cross at certain energy. Near this energy, the Landau quantization becomes peculiar since semiclassical trajectories, corresponding to individual branches, get coupled. We study this coupling as a function of proximity to the topological transition. Remarkably, the dependence on the proximity is strongly asymmetric reflecting the specifics of the behavior of the trajectories near the crossing. Equally remarkable, on one side of the transition, the magnitude of coupling is an oscillating function of this proximity. These oscillations can be interpreted in terms of the St{\"u}ckelberg interference. Scaling of characteristic detuning with magnetic length is also unusual. This unusual behavior cannot be captured by simply linearizing the Fermi contours near the crossing point.

Observation of room-temperature magnetic skyrmions in Pt/Co/W structures with a large spin-orbit coupling

Magnetic skyrmions have significant potential for applications in storage and logic devices, but the ability to control skyrmion motion is key to their success. To realize controlled skyrmion motion, vertical spin current-driven methods employing, e.g., the spin Hall or inverse spin galvanic effect, are efficient; thus, magnetic heterostructures featuring large spin-orbit torques are appealing. In this paper, we report on the observation of room-temperature magnetic skyrmions in Pt/Co/W multilayers. The interfacial Dzyaloshinskii-Moriya interaction was estimated to be $0.19\ifmmode\pm\else\textpm\fi{}0.05\phantom{\rule{0.16em}{0ex}}\mathrm{mJ}/{\mathrm{m}}^{2}$ based on the asymmetric domain-wall motion occurring upon the application of in-plane magnetic fields. The evolution of the magnetic structures from labyrinth domains to skyrmions with diameters of around 145 nm under magnetic fields was observed by performing Lorentz transmission electron microscopy. The skyrmion nucleation fields could be tuned by varying the repetition number. Large spin Hall angle systems such as Pt/Co/W multilayers are appealing for achieving current-driven skyrmion motion in future racetrack and logic applications.

Strain-induced gauge and Rashba fields in ferroelectric Rashba lead chalcogenide PbX monolayers ( X=S , Se, Te)

One of the exciting features of two-dimensional (2D) materials is their electronic and optical tunability through strain engineering. Previously, we found a class of 2D ferroelectric Rashba semiconductors $\mathrm{Pb}X$ ($X=\text{S}$, Se, Te) with tunable spin-orbital properties. In this work, based on our previous tight-binding (TB) results, we derive an effective low-energy Hamiltonian around the symmetry points that captures the effects of strain on the electronic properties of $\mathrm{Pb}X$. We find that strains induce gauge fields which shift the Rashba point and modify the Rashba parameter. This effect is equivalent to the application of in-plane magnetic fields. The out-of-plane strain, which is proportional to the electric polarization, is also shown to modify the Rashba parameter. Overall, our theory connects strain and spin splitting in ferroelectric Rashba materials, which will be important to understand the strain-induced variations in local Rashba parameters that will occur in practical applications.

Magnetic field inducing Zeeman splitting and anomalous conductance reduction of half-integer quantized plateaus in InAs quantum wires

We report on magnetic field dependence of half-integer quantized conductance plateaus (HQPs) in InAs quantum wires. We observed HQPs at zero applied magnetic field in InAs quantum wires fabricated from a high-quality InAs quantum well. The application of in-plane magnetic field causes Zeeman splitting of the HQP features, indicating that the origin of the observed HQP is not spontaneous spin polarization. Additionally we observe that conductance of the split HQPs decreases gradually as the in-plane magnetic field increases. We finally assume electron-electron interaction as a possible mechanism to account for the zero-field HQPs and the anomalous field dependence.

Positive quantum magnetoresistance in tilted magnetic field

Transport properties of highly mobile 2D electrons are studied in symmetric GaAs quantum wells placed in titled magnetic fields. Quantum positive magnetoresistance (QPMR) is observed in magnetic fields perpendicular to the 2D layer. Application of in-plane magnetic field produces a dramatic decrease of the QPMR. This decrease correlates strongly with the reduction of the amplitude of Shubnikov--de Haas resistance oscillations due to modification of the electron spectrum via enhanced Zeeman splitting. Surprisingly no quantization of the spectrum is detected when the Zeeman energy exceeds half of the cyclotron energy suggesting an abrupt transformation of the electron dynamics. Observed angular evolution of QPMR implies strong mixing between spin subbands. Theoretical estimations indicate that in the presence of spin-orbital interaction the elastic impurity scattering provides significant contribution to the spin mixing in GaAs quantum wells at high filling factors.

Magnetointersubband resistance oscillations in GaAs quantum wells placed in a tilted magnetic field

The magnetotransport of highly mobile 2D electrons in wide GaAs single quantum wells with three populated subbands placed in titled magnetic fields is studied. The bottoms of the lower two subbands have nearly the same energy while the bottom of the third subband has a much higher energy ($E_1\approx E_2<<E_3$). At zero in-plane magnetic fields magneto-intersubband oscillations (MISO) between the $i^{th}$ and $j^{th}$ subbands are observed and obey the relation $\Delta_{ij}=E_j-E_i=k\cdot\hbar\omega_c$, where $\omega_c$ is the cyclotron frequency and $k$ is an integer. An application of in-plane magnetic field produces dramatic changes in MISO and the corresponding electron spectrum. Three regimes are identified. At $\hbar\omega_c \ll \Delta_{12}$ the in-plane magnetic field increases considerably the gap $\Delta_{12}$, which is consistent with the semi-classical regime of electron propagation. In contrast at strong magnetic fields $\hbar\omega_c \gg \Delta_{12}$ relatively weak oscillating variations of the electron spectrum with the in-plane magnetic field are observed. At $\hbar\omega_c \approx \Delta_{12}$ the electron spectrum undergoes a transition between these two regimes through magnetic breakdown. In this transition regime MISO with odd quantum number $k$ terminate, while MISO corresponding to even $k$ evolve $continuously$ into the high field regime corresponding to $\hbar\omega_c \gg \Delta_{12}$

Impedance Variation with Subjecting to Normal Field for the Stepped Giant Magnetoimpedance Element

In this paper, an impedance variation for the stepped giant magnetoimpedance (GMI) element, when subjecting to a strong normal field, is reported. The stepped GMI element is an element which has an impedance-step property, which happens simultaneously with a change of magnetic domain. The strong normal field varies a profile of the sharp dip-point of the impedance-step, that is to say the normal field can control the dynamics of domain change of the element. The application of normal field also arises at a lower impedance state, which is expected as a hidden in-plane inclined Landau-Lifshitz-domain. This lower impedance state disappears by the application of in-plane magnetic field, which is larger than a certain value of threshold in absolute, and does not appear until the next application of the normal field. This element was proposed to apply a sensor with memory function in our prior work. The method reported in this paper would give a special function for the sensor application.

Pinning-Mode Resonance of a Skyrme Crystal near Landau-Level Filling Factorν=1

Microwave pinning-mode resonances found around integer quantum Hall effects, are a signature of crystallized quasiparticles or holes. Application of in-plane magnetic field to these crystals, increasing the Zeeman energy, has negligible effect on the resonances just below Landau-level filling ν=2, but increases the pinning frequencies near ν=1, particularly for smaller quasiparticle or hole densities. The charge dynamics near ν=1, characteristic of a crystal order, are affected by spin, in a manner consistent with a Skyrme crystal.

Controlling Double Vortex States in Low-Dimensional Dipolar Systems

The reversal process of the chirality of each opposite vortex belonging to a double vortex state in ferromagnetic hysterons, via the application of in-plane magnetic fields, is reported. Simulations reveal that such a process involves the formation of four intermediate states, including original ones. Hysteresis loops can occur only in a counterclockwise fashion because of one of these intermediate states. Double vortex states can also be controlled by electric fields in ferroelectric nanostructures of different shapes, but with some key differences with respect to the ferromagnetic case.

Signatures of composite-fermion metals in electron bilayers at νT=1

Composite-fermion metals occur in the quantum Hall bilayers at total Landau level filling fraction ν T=1 as the tunneling gap Δ SAS collapses by application of in-plane magnetic fields. Experimental evidence is obtained from the observation of a spin continuum below the Zeeman energy by resonant inelastic light scattering. These low-lying spin modes are assigned to quasi-particle excitations, where spin and composite-fermion Landau level index change simultaneously.

Anisotropic Transport of Two-Dimensional Hole System in Higher Landau Levels: Effect of In-Plane Magnetic Field

We have observed anisotropic states of two-dimensional hole systems (2DHS) in higher Landau levels which are analogous to those found in 2D electron systems (2DES), the so-called stripe phase. Application of in-plane magnetic field along the hard (high resistance) direction stabilizes the anisotropic state, while that along the easy axis hardly affect the state. This is in contrast to the corresponding 2DES case where the stripe is easily reoriented by an in-plane magnetic field, and suggests that the built-in symmetry-breaking cause which favors a particular stripe orientation acts more strongly in 2DHS than in 2DES. We discuss the possible origin of the orientational pinning.

Seeing emergent phases in quantum Hall double layers

We review recent studies by optics methods of emergent phases in the quantum Hall (QH) regimes of double layers with finite tunneling at Landau level filling factor ν=1. In measurements of spin excitations by inelastic light scattering and of elastically scattered Rayleigh light under the application of in-plane magnetic fields, we uncovered evidence of a quantum phase transition that occurs when a many-body tunneling gap collapses. The transformation can be regarded as a transition from an incompressible highly correlated QH state to a compressible composite-fermion bilayer system. The correlated QH state is characterized by the presence of populations of bound electron-hole pairs across the tunneling gap. Quantitative determinations of the density of such excitonic pairs are obtained from inelastic light scattering spectra of spin excitations. The correlated QH state displays resonant Rayleigh scattering with unusual temperature dependence.

Observation of Collapse of Pseudospin Order in Bilayer Quantum Hall Ferromagnets

The Hartree-Fock paradigm of bilayer quantum Hall states with finite tunneling at filling factor nu=1 has full pseudospin ferromagnetic order with all the electrons in the lowest symmetric Landau level. Inelastic light scattering measurements of low energy spin excitations reveal major departures from the paradigm at relatively large tunneling gaps. The results indicate the emergence of a novel correlated quantum Hall state at nu=1 characterized by reduced pseudospin order. Marked anomalies occur in spin excitations when pseudospin polarization collapses by application of in-plane magnetic fields.

Destabilizing Effect of In-Plane Magnetic Field on Panel Flutter

ABSTRACTDestabilizing effect of magnetic damping on the supersonic panel flutter is investigated. The linear piston theory is available to formulate the air force at high Mach numbers. A plate in supersonic flow can be stabilized by reducing the compression force perpendicular to the flow. However, once the dynamic pressure parameter exceeds some critical value, the time rate of motion becomes complex then the flutter occurs. In this paper, the strength of in-plane magnetic field to reduce the panel flutter under higher dynamic pressure parameter is determined. Due to the complexity in finding the exact solution of plate motion, Galerkin solution with different terms of truncation is adopted herein. Therefore, the exact solution can be obtained by using the four-term solution as an initial value. The most attractive feature is that the supersonic flutter can be avoided efficiently through the application of in-plane magnetic field.