In-plane Magnetization Components Research Articles

Toward 3D magnetic force microscopy: Simultaneous torsional cantilever excitation to access a second, orthogonal stray field component

Magnetic force microscopy (MFM) is long established as a powerful tool for probing the local stray fields of magnetic nanostructures across a range of temperatures and applied stimuli. A major drawback of the technique, however, is that the detection of stray fields emanating from a sample’s surface rely on a uniaxial vertical cantilever oscillation, and thus are only sensitive to vertically oriented stray field components. The last two decades have shown an ever-increasing literature fascination for exotic topological windings where particular attention to in-plane magnetic moment rotation is highly valuable when identifying and understanding such systems. Here, we present a method of detecting in-plane magnetic stray field components, by utilizing a split-electrode excitation piezo that allows the simultaneous excitation of a cantilever at its fundamental flexural and torsional modes. This allows for the joint acquisition of traditional vertical mode images and a lateral MFM where the tip–cantilever system is only sensitive to stray fields acting perpendicular to the torsional axis of the cantilever.

Ion-irradiation-induced field-free magnetization switching in synthetic antiferromagnets by spin–orbit torque

The perpendicularly magnetized synthetic antiferromagnets (SAFs) are expected to be ideal materials for magnetic random-access memory (MRAM) due to the low cross-talk noise and the high recording density. Normally, an in-plane magnetic field is required to break the inversion symmetry for deterministic magnetization switching in perpendicular SAFs by SOTs, which is undesirable for applications. In this work, the ion-irradiation method was adopted to engineer the interface of a perpendicularly magnetized Pt/Co/Pt/Ru/Pt/Co/Ta SAF to achieve the filed-free switching of the magnetization via the in-plane magnetization component of top-Co layer, which provides an in-plane effective field to bottom-Co layer and breaks the symmetry. Furthermore, with the increase of ion fluence, the critical switching current density decreases, which is consistent with the increase of spin Hall angle induced by ion-irradiation measured by the harmonic Hall voltage method. These results indicate that ion irradiation is a promising approach for realizing field-free magnetization switching in SAFs driven by SOTs and has potential application in SOT-based spintronic devices.

Manipulation of topological spin textures in centrosymmetric rare-earth magnets

Topologically protected magnetic skyrmions are expected to be used in the next-generation spintronic devices. Realizing their nucleation and manipulation at room temperature is fundamental for future practical applications. Here, using in situ Lorentz transmission electron microscopy and micromagnetic simulation, we demonstrate that magnetic biskyrmions can spontaneously exist at room temperature in Nd1–xTbxCo5 (x = 0.3, 0.5) alloys. The spontaneous biskyrmions are controllably obtained over a wide temperature range across room temperature by switching atomic chemical environment. Furthermore, the density of biskyrmions can be tuned by a small magnetic field. High-density biskyrmions are stimulated to form in the thinner region at room temperature by introducing an in-plane magnetic field component. These results provide valuable insights into the manipulation of topological states, which is of great significance to their practical applications.

Majorana zero modes in a magnetic and superconducting hybrid vortex

We propose and investigate a new platform for the realization of Majorana zero modes in a thin-film heterostructure composed of an easy-plane ferromagnet and a superconductor with spin-orbit coupling. The system can support an energetically favorable bound state comprising a magnetic vortex and a superconducting vortex. We show that a hybrid vortex thus created can host a robust zero-energy Majorana bound state at its core over a wide range of parameters, with its partner zero mode located at the boundary of a disk-shaped topological region. We identify a novel mechanism underlying the formation of the topological phase that, remarkably, relies on the orbital effect of the magnetization field and not on the usual Zeeman effect. The in-plane components of magnetization couple to electrons as a gauge potential with nonzero curl, thus creating an emergent magnetic field responsible for the gapped topologically nontrivial region surrounding the vortex core. Our construction allows the mobility of magnetic vortices to be imposed on the Majorana zero mode at the core of the superconducting vortex. In addition, the system shows a rich interplay between magnetism and superconductivity which might aid in developing future devices and technologies.

Giant anisotropic magnetoresistance at low magnetic fields in a layered semiconductor

Materials exhibiting a drastic change in electrical resistivity depending on magnetic-field direction is of great interest and is rarely seen in real systems. We report the huge anisotropic magnetoresistance ratio exceeding 7500 at low-magnetic field of 0.4 T at 2 K in the layered magnetic semiconductor ${\mathrm{CeTe}}_{1.83}{\mathrm{Sb}}_{0.17}$ with extremely low carrier density in charge-density-wave state. We found that the electrical resistivity is governed only by the out-of-plane component of magnetization and steeply decreases nearly four orders of magnitude in the magnetic field along the $c$ axis. In contrast, it is quite insensitive to the in-plane component of magnetization and huge anisotropy is preserved even in a much higher magnetic field.

Magnetic domains and unusual hysteresis loops of yttrium iron garnet crystals revealed by magneto-optic effects

I present a magneto-optic effect study of magnetic domains in a ferrimagnetic yttrium iron garnet crystal at different stages of a hysteresis loop. By measuring the Faraday effect in response to the out-of-plane component and Kerr effects to the in-plane components of the sample magnetization, I examined the evolution of magnetic domains during a hysteresis loop in an in-plane external magnetic field. I found that crystalline anisotropy, magneto-static energy, and the presence of movable domain walls play indispensable roles in the domain orientation, particularly when the external field is near zero, and have led to seemingly unusual appearances of hysteresis loops.

Interpretation of Kerr Microscopic Domain Contrast on Curved Surfaces

In this letter we address a technical peculiarity of wide-field magneto-optical Kerr microscopy, which may easily lead to a misinterpretation of the domain contrast on curved surfaces. On the example of circumferentially magnetized domains in ferromagnetic microwires we show that the checkerboard domain pattern, which typically shows up in polar Kerr sensitivity, is caused by the superposition of longitudinal Kerr contrasts that arise from in-plane magnetization components and inclined light incidence rather than from the magnetization components perpendicular to the focal plane as claimed in the literature. Experimental ways to avoid such peculiar contrasts are demonstrated.

V-MOKE magnetometry: a solution for devices with fixed electromagnet

We introduce a novel method aimed to obtain the scale factor between in-plane magnetization components, indispensable for vectorial-magneto-optic Kerr effect (v-MOKE) experiments, convenient for experimental setups where it is difficult or unfeasible to rotate the electromagnet. Unlike the original method, in our proposal the electromagnet (and all other optical components) are fixed, extending in this way the possibility to implement v-MOKE magnetometry. Two films, FePt 9 and 100 nm thickness, were used as sample probes, presenting in-plane magnetic uniaxial anisotropy and in-plane magnetic isotropy, respectively. All experiments were carried out at room temperature and employing an home-made MOKE system. We also introduce a closed mathematical expression for the scale factor linking both magnetization components in terms of experimental and sample dependent parameters.

Anisotropy of the in-plane g -factor of electrons in HgTe quantum wells

The results of experimental studies of the Shubnikov-de Haas (SdH) efect in the (013)-HgTe/Hg$_{1-x}$Cd$_x$Te quantum wells (QWs) of electron type of conductivity both with normal and inverted energy spectrum are reported. Comprehensive analysis of the SdH oscillations measured for the different orientations of magnetic field relative to the quantum well plane and crystallographic exes allows us to investigate the anisotropy of the Zeeman effect. For the QWs with inverted spectrum, it has been shown that the ratio of the spin splitting to the orbital one is strongly dependent not only on the orientation of the magnetic field relative to the QW plane but also on the orientation of the in-plane magnetic field component relative to crystallographic axes laying in the QW plane that implies the strong anisotropy of in-plane g-factor. In the QW with normal spectrum, this ratio strongly depends on the angle between the magnetic field and the normal to the QW plane and reveals a very slight anisotropy in the QW plane. To interpret the data, the Landau levels in the tilted magnetic field are calculated within the framework of four-band \emph{kP} model. It is shown that the experimental results can be quantitatively described only with taking into account the interface inversion asymmetry.

Surface modification of FePt(Ag, C) granular film by ultrathin B4C capping layer

The in-plane magnetic component in FePt-40 vol% (Ag, C) granular film was caused by lower ordering degree which lower the magnetic anisotropy field and out-of-plane coercivity (Hc = 23.6 kOe). To inhibit the FePt grains with second nucleation, random texture and in plane c-axis, the ultrathin B4C layer with thickness of 1 nm was capped. After surface modification, the FePt-40 vol% (Ag, C) film illustrates high perpendicular magnetic anisotropy (Ku = 1.75 × 107 erg/cm3) and out-of-plane coercivity (Hc = 28.8 kOe). The in-plane remanence magnetic moment is small and the tiny magnetization kink at zero field was not observed in easy-axis loop of 6 nm thick FePt-40 vol% (Ag, C) film. The ordering degree and the average surface roughness of FePt-(Ag, C) films were improved by surface diffusion of B4C which deposited at 470 °C and post-annealed for 2 min. Further, the perpendicular magnetic anisotropy and out-of-plane coercivity of FePt-(Ag, C) films were enhanced significantly. The TiOx are more favorable than TiN in MgTiON layer due to formation enthalpy, part of N atoms was diffused and incorporated in the FePt lattice evidenced in high angle angular dark field mapping. After post annealing, the released N atoms cause lots of vacancies and defects inside FePt film which promote the ordering degree.

Magnetic properties and spin-orbit-torque-induced magnetization switching in Ta/MnGa grown on Cr and NiAl buffer layers

We investigate the magnetic properties and spin-orbit-torque-induced (SOT-induced) magnetization switching in Ta/MnGa/Cr and Ta/MnGa/NiAl structures. Out-of-plane hysteresis loops for the Ta/MnGa/Cr (NiAl) structures are skewed (square). In-plane currents I are applied to Hall devices made of structures exposed to in-plane magnetic fields Hin along the channel direction. Clear asymmetric magnetization switching with respect to the polarity of I and Hin is detected for the Ta/MnGa/NiAl device. Similar asymmetric magnetization switching is observed for the Ta/MnGa/Cr device, although the magnetization is partially switched regardless of the polarity of I and Hin. These results suggest that an in-plane magnetization component opposite to Hin is present in the Cr-buffer structure and that the formation of such a component is suppressed in the NiAl-buffer structure.

Magneto-optical Kerr effect and nuclear resonant scattering study of uni-directional anisotropy in hard-soft magnetic bilayers

The present work reports the unconventional exchange bias (EB) phenomena in an exchange-coupled hard and soft magnetic bilayer system and the tunability of EB. The EB phenomena, i.e., shifting of the hysteresis loop of the soft (Fe) layer is observed when the hard magnetic (L10 FePt) layer is under the remanent state indicating the development of unidirectional anisotropy. The nuclear resonant scattering measurements clearly reveal the development of unidirectional anisotropy in the soft magnetic (Fe) layer, when the hard magnetic layer is under the remanent state. The magnetization reversal process is investigated by measuring two in-plane orthogonal components of magnetization, i.e., parallel (M∥) and perpendicular (M⊥) to the applied field using the magneto-optical Kerr effect (MOKE). When the magnetic field is applied parallel (antiparallel) to the biasing field direction, (HSAT) magnetization reversal is nonuniform, and on the other hand, the rotation of magnetization is observed when the magnetic field is applied away from the HSAT direction. In addition, the sign inversion of the M⊥ component is observed when the magnetic field is applied at the same angle on either side of the HSAT direction, which clearly imply the change in handedness of the chirality of spin structure during the magnetization reversal of the soft layer. Further, it is observed that the EB decreases with the increase of soft magnetic (Fe) layer thickness, demonstrating the tunable nature of EB phenomena even in these unconventional systems.

Time-Resolved Imaging of Magnetoelastic Waves by the Cotton-Mouton Effect

Time-resolved magneto-optical (TRMO) imaging with ultrashort laser pulses now allows direct observation of the excitation, propagation, and relaxation dynamics of magnetization, with the details of excitation still being studied. This article shows how to image the in-plane component of magnetization, modulated by propagating spin waves, via the birefringence that arises in a transverse magnetic field. The authors use this method to resolve the contribution from magnetoelastic coupling in an out-of-plane-magnetized film. This technique extends the scope of TRMO imaging for investigating laser-induced magnetization dynamics, which will enable work in spintronics.

Field-Tunable 0-\u03c0-Transitions in SnTe Topological Crystalline Insulator SQUIDs

The manifestation of spin-orbit interactions, long known to dramatically affect the band structure of heavy-element compounds, governs the physics in the surging class of topological matter. A particular example is found in the new family of topological crystalline insulators. In this systems transport occurs at the surfaces and spin-momentum locking yields crystal-symmetry protected spin-polarized transport. We investigated the current-phase relation of SnTe thin films connected to superconducting electrodes to form SQUID devices. Our results demonstrate that an assisting in-plane magnetic field component can induce 0-π-transitions. We attribute these findings to giant g-factors and large spin-orbit coupling of SnTe topological crystalline insulator, which provides a new platform for investigation of the interplay between spin-orbit physics and topological transport.

Composite fermion liquid to Wigner solid transition in the lowest Landau level of zinc oxide

Interactions between the constituents of a condensed matter system can drive it through a plethora of different phases due to many-body effects. A prominent platform for it is a dilute two-dimensional electron system in a magnetic field, which evolves intricately through various gaseous, liquid and solid phases governed by Coulomb interaction. Here we report on the experimental observation of a phase transition between the composite fermion liquid and adjacent magnetic field induced phase with a character of Wigner solid. The experiments are performed in the lowest Landau level of a MgZnO/ZnO two-dimensional electron system with attributes of both a liquid and a solid. An in-plane magnetic field component applied on top of the perpendicular magnetic field extends the Wigner-like phase further into the composite fermion liquid phase region. Our observations indicate the direct competition between a composite fermion liquid and a Wigner solid formed either by electrons or composite fermions.

Imaging spin-resolved cyclotron trajectories in the InSb two-dimensional electron gas

We consider spin-resolved cyclotron trajectories in a magnetic focusing device with quantum point source and drain contacts defined within the InSb two-dimensional electron gas and their mapping by the scanning gate microscopy. Besides the perpendicular component of the external magnetic field which bends the electron trajectories we consider an in-plane component which introduces the spin-dependence of the cyclotron radius. We demonstrate that the focusing conductance peaks become spin-split by the in-plane magnetic field component of the order of a few tesla and that the spin-resolved trajectories can be traced separately with the conductance mapping.

Interplay of magnetic anisotropies on the magnetostrictive behavior of Fe–Co thin films

This paper reports the structure, microstructure, domain imaging and magnetostrictive properties of Fe50Co50 thin grown on Si substrates with different thicknesses namely 40, 80, 100 and 120 nm. Structural studies revealed that the films are crystalline in nature with bcc type structure. Magnetization studies exhibited predominant in-plane magnetic anisotropy for all the films. In addition to this films grown with higher thicknesses also showed co-existence of out-of-plane magnetic anisotropy along with in-plane magnetic components. Angle dependent hysteresis measurements indicated presence of weak uni-axial magnetic anisotropy along the plane for all the films. Longitudinal magneto-optic Kerr microscopy studies revealed nucleation of reverse domains for the film grown with low thickness. Wide band domains with few zig–zag branched features have been observed for the films grown with higher thicknesses. Magnetic force microscopy investigations along the out-of-plane direction showed increase in magnetic phase contrast with increase in film thicknesses. Magnetostriction derived from the deflection measurements are found to decrease with increase in film thicknesses. Presence of competing anisotropies has been found to be prominent reason for the decrease in the magnetostriction with increase in film thickness.

3D Magnetic Field Reconstruction Methodology Based on a Scanning Magnetoresistive Probe.

The present work provides a detailed description on quantitative 3D magnetic field reconstruction using a scanning magnetoresistance microscopy setup incorporating a 19.5 m × 2.5 m magnetoresistive sensor. Therefore, making use of a rotation stage, 11 nm thick ferromagnetic CoFe elements with 20 m × 5 m planar size were measured along different sensor axes and converted into cartesian coordinate magnetic field components by use of the analytical coordinate transform equations. The reconstruction steps were followed and validated by numerical simulations based on a field averaging model caused by a non-negligible sensor volume. Detailed in-plane magnetic component reconstruction with ability to reconstruct sub-micrometer features is achieved. A discussion on the limiting factors for optimal resolution is presented.

X-ray scattering study on the electric field-induced interfacial magnetic anisotropy modulation at CoFeB / MgO interfaces

The electric field-induced modifications of magnetic anisotropy in CoFeB/MgO systems are studied using X-ray resonant magnetic scattering and magneto-optical Kerr effect. Voltage dependent changes of the magnetic anisotropy of −12.7 fJ/Vm and −8.32 fJ/Vm are observed for Ta/CoFeB/MgO and Hf/CoFeB/MgO systems, respectively. This implies that the interfacial perpendicular magnetic anisotropy is reduced (enhanced) when electron density is increased (decreased). X-ray resonant magnetic scattering measurements reveal that the small in-plane magnetic component of the remanent state of CoFeB/MgO systems with weak magnetic anisotropy changes depending on the applied voltage leading to modification of the magnetic anisotropy at the CoFeB/MgO interface.

Scanning electron microscopy with polarization analysis for multilayered chiral spin textures

We show that scanning electron microscopy with polarization analysis (SEMPA) that is sensitive to both in-plane magnetization components can be used to image the out-of-plane magnetized multi-domain state in multilayered chiral spin textures. By depositing a thin layer of Fe on top of the multilayer, we image the underlying out-of-plane domain state through the mapping of its stray fields in the Fe. We also demonstrate that SEMPA can be used to image the domain wall chirality in these systems after milling away the capping layer and imaging the topmost magnetic layer directly.