In-plane Magnetization Research Articles

How Saturn could create dense rings after the emergence of its magnetic field. The Tchernyi-Kapranov effect: mechanism of magnetic anisotropic accretion

The origin of Saturn’s dense rings is still unclear. Here we propose a mechanism of the genesis of Saturn’s dense rings from ice particles (chunks) of the protoplanetary cloud. It shows how Saturn could create rings after the emergency of its magnetic field. We take into account the force of diamagnetic expulsion and the Tchernyi-Kapranov effect: the process of magnetic anisotropic accretion. The force of diamagnetic expulsion acts on the particles together with the gravitational and centrifugal force. As a result, the orbits of ice particles of different sizes move into the plane of magnetic equator, where their energy is minimal. Ultimately, every particle acquires its stable orbit in magnetic equator plane, and the net force prevents its radial and vertical shift. The process described here is likely to contribute to the genesis of a stable disk-shaped structure of dense rings, formation of sharp edges of rings and gaps, and separation of particles (chunks) in rings. Previous theories are not questioned here, but they are complemented with the magnetic interaction, which accounts for the Tchernyi-Kapranov effect: mechanism of magnetic anisotropic accretion of ice particles.

Controllable unidirectional magnetoresistance in ferromagnetic films with broken symmetry

Spin-related unidirectional magnetoresistance (UMR) exhibits nonreciprocal transport to either charge current or magnetization reversal, providing a potential application for direct electrical readout of in-plane magnetization using simple two-terminal geometry. To achieve such a UMR, it is usually believed that an adjacent heavy metal or other materials with strong spin-orbit coupling (SOC) as the spin polarizer is indispensable, leading to most efforts on multilayer structures rather than single-layer ferromagnetic films. Here, we report the observation of UMR in a single CoPt film by introducing a vertical composition gradient to break the structural inversion symmetry. Moreover, unlike conventional heavy-metal/ferromagnetic-metal bilayer films, the UMR in the CoPt film with a positive Co composition gradient is controllable as a function of current amplitude, which shows the decrease, sign reversal, and then enhancement with the increment of current density. These results reveal two competing UMR mechanisms with opposite signs in electrical current dependency, i.e., bulk Rashba effect induced by composition gradients and anomalous Nernst effect driven by a vertical temperature gradient. Our work provides a promising way to manipulate the UMR in a single ferromagnetic film with the combination of charge-spin conversion and magnetothermal effect.

Large Spin Hall Angle in Sputtered BiSb Topological Insulator on Top of Various Ferromagnets With In-Plane Magnetization for SOT Reader Application

A spin-orbit torque (SOT) reader using the inverse spin Hall effect was recently proposed as a candidate for magnetic recording beyond 4 Tbit/in2. However, SOT readers using conventional heavy metals have small output voltage and low signal-to-noise ratio (SNR) due to the small spin Hall angles of heavy metals. Demonstrated in this work is a large spin Hall angle of 2.6–5.1 in sputtered BiSb, a topological insulator, on top of various ferromagnets with in-plane magnetization. The spin Hall angle of BiSb is much larger than that of heavy metals, which is promising for SOT readers with large output and high SNR.

Destabilizing Influence of the Neutral Winds for the Midnight and Post‐Midnight Ionospheric Irregularities in Brazil Sector

AbstractMidnight and post‐midnight ionospheric irregularities are observed over Brazil sector during the June solstice of solar inactive years. The prevailing nighttime winds in the magnetic meridional plane (magnetic meridional winds) are experimentally described as a trans‐equatorial wind, and superposed a convergent/equatorward component that emerges after 03 LT. Further computation of the growth rate of the generalized Rayleigh‐Taylor (GRT) instability well explains the local time dependent irregularities observed. Our analysis indicates that the trans‐equatorial wind before midnight uplifts the ionosphere in the upwind (northern) hemisphere, whereas the expected downwelling in the conjugate hemisphere is almost unseen. The wind hence decreases the field‐line integrated Pedersen conductivity and promotes the midnight instability, instead of suppressing it as conventionally known. After 03 LT, the convergent/equatorward component also provides an unstable condition, consistent with the theory that a meridional wind profile with a negative latitudinal gradient will destabilize the ionosphere. The growth rate gets lower as the neutral winds weakened with increasing solar activity, but seemingly insufficient to explain the much fewer instabilities observed in 2012 than in 2009. Other solar activity dependent factors need to be taken into account in addition to the growing process of the GRT instability in the F region.

Thickness dependent microstructural and magnetic studies of iron embedded PVA nanocomposite films

This paper presents the structural and magnetic properties of polyvinyl alcohol/iron (PVA/Fe) nanocomposite films. Iron (Fe) films of different thicknesses were deposited on a PVA substrate using ion beam sputtering. The Fe nanoparticle layer thickness ranges from 3 to 50 nm on the PVA substrate. Grazing incidence x-ray diffraction has been carried out to study the structural behavior of the prepared films. An atomic force microscope records the indicated remarkable change in the roughness of the nanocomposite film as a result of initiation of vertical growth of sputtered Fe nanoparticles.Magneto-optic Kerr effect (MOKE) magnetometry and MOKE spectroscopy have been employed to evaluate the magnetic property and simultaneously study the real time growth of the magnetic domain structure for both 0° and 90° azimuthal angles. MOKE microscopic images indicated the magnetization reversal commensurate with the hysteresis loop of the nanocomposites. All the films show soft ferromagnetic behavior. Gradual development of the domain structure is observed in the MOKE micrograph with the increase in the thickness of Fe nanoparticle deposition. Ex situ magnetic force micrographs of the magnetic domain structures supported the observation of MOKE microscopic studies, which indicated switching of in-plane magnetization to out-of-plane magnetization near an Fe nanoparticle deposition thickness of 40 nm. The PVA matrix appears to be an effective material to support the growth of magnetic properties in the PVA/Fe nanocomposite system. The evolution of Fe nanostructures on PVA and the resulting magnetic behavior have been discussed.

Engineering axion insulator and other topological phases in superlattices without inversion symmetry

We study theoretically the interplay between magnetism and topology in three-dimensional HgTe/MnTe superlattices stacked along the (001) axis. Our results show the evolution of the magnetic topological phases with respect to the magnetic configurations. An axion insulator phase is observed for the antiferromagnetic order with the out-of-plane N\'eel vector direction below a critical thickness of MnTe, which is the ground state amongst all magnetic configurations. Defining $T$ as the time-reversal symmetry, this axion insulator phase is protected by a magnetic two-fold rotational symmetry $C_2{\cdot}T$. The axion insulator phase evolves into a trivial insulator as we increase the thickness of the magnetic layers. By switching the N\'eel vector direction into the $ab$ plane, the system realizes different antiferromagnetic topological insulators depending on the thickness of MnTe. These phases feature gapless surface Dirac cones shifted away from high-symmetry points on surfaces perpendicular to the N\'eel vector direction of the magnetic layers. In the presence of ferromagnetism, the system realizes a magnetic Weyl semimetal and a ferromagnetic semimetal for out-of-plane and in-plane magnetization directions, respectively. We observe large anomalous Hall conductivity in the presence of ferromagnetism in the three-dimensional superlattice.

Layer-dependent zero-line modes in antiferromagnetic topological insulators

Recently, the magnetic domain walls have been experimentally observed in antiferromagnetic topological insulators MnBi$_2$Te$_4$, where we find that the topological zero-line modes (ZLMs) appear along the domain walls. Here, we theoretically demonstrate that these ZLMs are layer-dependent in MnBi$_2$Te$_4$ multilayers. For domain walls with out-of-plane ferromagnetism, we find that ZLMs are equally distributed in the odd-number layers. When domain walls possess in-plane magnetization, the ZLMs can also exist in even-number layers due to in-plane mirror-symmetry breaking. Moreover, the conductive channels are mainly distributed in the outermost layers with increasing layer thickness. Our findings lay out a strategy in manipulating ZLMs and also can be utilized to distinguish the corresponding magnetic structures.

Quantum Oscillation and Electronic Structure of Sn4As3 and Sn4P3

We report the magnetotransport properties and electronic structures of the single crystals of Sn4As3 and Sn4P3. The magnetization curves display strong de Haas–van Alphen oscillations at low temperatures and high magnetic fields. The oscillation frequencies and corresponding Fermi surfaces (FSs) are identified from the analysis of the oscillations. The in-plane magnetization of Sn4As3 shows the split of FSs induced by nonsymmetric spin–orbit interaction. The extracted cyclotron effective masses are very small and in the range 0.03–0.11 me. First-principles calculations reveal the electronic structures and topological properties. Large transverse magnetoresistance (MR) has also been observed in Sn4As3 and Sn4P3. The Hall measurements eliminate the possibility of electron–hole compensation. It is suggested that the large MR mainly originates from the open FSs.

Raman scattering signatures of strong spin-phonon coupling in the bulk magnetic van der Waals material CrSBr

Magnetic excitations in layered magnetic materials that can be thinned down the two-dimensional (2D) monolayer limit are of high interest from a fundamental point of view and for applications perspectives. Raman scattering has played a crucial role in exploring the properties of magnetic layered materials and, even-though it is essentially a probe of lattice vibrations, it can reflect magnetic ordering in solids through the spin-phonon interaction or through the observation of magnon excitations. In bulk CrSBr, a layered A type antiferromagnet (AF), we show that the magnetic ordering can be directly observed in the temperature dependence of the Raman scattering response i) through the variations of the scattered intensities, ii) through the activation of new phonon lines reflecting the change of symmetry with the appearance of the additional magnetic periodicity, and iii) through the observation, below the Neel temperature (TN) of second order Raman scattering processes. We additionally show that the three different magnetic phases encountered in CrSBr, including the recently identified low temperature phase, have a particular Raman scattering signature. This work demonstrates that magnetic ordering can be observed directly in the Raman scattering response of bulk CrSBr with in-plane magnetization, and that it can provide a unique insight into the magnetic phases encountered in magnetic layered materials.

Correlation-Driven Topological Transition in Janus Two-Dimensional Vanadates

The appearance of intrinsic ferromagnetism in 2D materials opens the possibility of investigating the interplay between magnetism and topology. The magnetic anisotropy energy (MAE) describing the easy axis for magnetization in a particular direction is an important yardstick for nanoscale applications. Here, the first-principles approach is used to investigate the electronic band structures, the strain dependence of MAE in pristine VSi2Z4 (Z = P, As) and its Janus phase VSiGeP2As2 and the evolution of the topology as a function of the Coulomb interaction. In the Janus phase the compound presents a breaking of the mirror symmetry, which is equivalent to having an electric field, and the system can be piezoelectric. It is revealed that all three monolayers exhibit ferromagnetic ground state ordering, which is robust even under biaxial strains. A large value of coupling J is obtained, and this, together with the magnetocrystalline anisotropy, will produce a large critical temperature. We found an out-of-plane (in-plane) magnetization for VSi2P4 (VSi2As4), and an in-plane magnetization for VSiGeP2As2. Furthermore, we observed a correlation-driven topological transition in the Janus VSiGeP2As2. Our analysis of these emerging pristine and Janus-phased magnetic semiconductors opens prospects for studying the interplay between magnetism and topology in two-dimensional materials.

Magnetic and absorption properties in hundreds of megahertz band for a FeSi@SiO2 composite with brick stacking structure and crystallographic orientation

Electromagnetic (EM) pollution in the 0.1–1 GHz band is increasing with the rapid advancement in 5G communication technology. However, there are barely any absorption materials in the said band. Herein, we report a high-performance EM wave absorption composite with brick stacking structure and crystallographic orientation prepared using flake-like FeSi@SiO2 particles. The permeability of this composite with such novel structure is increased by more than ten times compared with conventional composites, reaching 42 at 1 MHz. The reflection loss (RL) can reach −40 dB around 0.3 GHz and the effective absorption bandwidth (RL 〈−10) can cover 0.2–1 GHz, which is significantly better than previous reports. Such a high permeability is ascribed to easy magnetization plane and low demagnetization factor parallel to the flake-like particles plane. The excellent absorption is attributed to the intrinsic loss introduced by the enhanced domain wall resonance, and the interference loss generated by quarter-wavelength cancellation. Particularly, the composite proposed in this study has great business and application value in the field of EM wave absorption, and the preparation method can be extended to other EM wave absorption composites, which provides a considerable guidance for the preparation of magnetic metallic absorption composites.

A comprehensive view on real-time magnetic resonance-guided flutter ablation image planes from an electrophysiological perspective.

A comprehensive view on real-time magnetic resonance-guided flutter ablation image planes from an electrophysiological perspective.

Iterative Optimization Algorithm to Design Biplanar Coils for Dynamic Magnetoencephalography

In this article, an iterative optimization algorithm is proposed to design biplanar coils, which is used for dynamic magnetoencephalography to compensate for residual fields in the magnetic shielding room. The effects of magnetic shielding layers and plane’s side length on the uniformity are both considered for designing coils. The iterative calculation is used to minimize the side length of the coil plane. The biplanar coils with 1.3-m side length are designed, which consist of three homogeneous-field coils ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$B_{x}, B_{y},\; { \rm and }\; B_{z}\; { \rm coils }$</tex-math></inline-formula> ) and five gradient-field coils ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$dB_{x}/dy, dB_{x}/dz, dB_{y}/dy, dB_{y}/dz,\; { \rm and }\; dB_{z}/dz\; { \rm coils }$</tex-math></inline-formula> ). The coil system can produce homogeneous and gradient fields within 1% error over the volume of 40 cm × 40 cm × 40 cm. Through active magnetic shielding, the central field inside the magnetic room is reduced from 7.56 to 0.17 nT, and standard deviation from the mean value in the target area falls from 1.366 to 0.177 nT. The dynamic auditory stimulation experiment proves that the biplanar coil system will improve the quality of the evoked signals.

Anisotropic angle-dependent Andreev reflection at the ferromagnet/superconductor junction on the surface of topological insulators

We theoretically demonstrate that a ferromagnetic/superconductor junction on the surface of three-dimensional topological insulators (3D TIs) has an anisotropic angle-dependent Andreev reflection when the in-plane magnetization has a component perpendicular to the junction. In the presence of in-plane magnetization, the Dirac cone’s location adjusts in the k-space, whereas its out-of-plane component induces a gap. This movement leads to the anisotropic angle-dependent Andreev reflection and creates an anomalous Hall conductance flows parallel to the interface. Also, an indirect gap induces in the junction, which removes the transport signatures of Majorana bound states. Because of the full spin-momentum locking of Dirac fermions on the surface of 3DTIs, a torque that called Andreev Transfer Torque (ATT) imposes on the junction. Moreover, we propose a setup to detect them experimentally.

Optical Creation of Skyrmions by Spin Reorientation Transition in Ferrimagnetic CoHo Alloys.

Manipulating magnetic skyrmions by means of a femtosecond (fs) laser pulse has attracted great interest due to their promising applications in efficient information-storage devices with ultralow energy consumption. However, the mechanism underlying the creation of skyrmions induced by an fs laser is still lacking. As a result, a key challenge is to reveal the pathway for the massive reorientation of magnetization from trivial to nontrivial topological states. Here, we studied a series of ferrimagnetic CoHo alloys and investigated the effect of a single laser pulse on the magnetic states. Thanks to the time-resolved magneto-optical Kerr effect and imaging techniques, we demonstrate that the laser-induced phase transitions from single domains into a topological skyrmion phase are mediated by the transient in-plane magnetization state, in real time and space domains, respectively. Combining experiments and micromagnetic simulations, we propose a two-step process for creating skyrmions through laser pulse irradiation: (i) the electron temperature enhancement induces a spin reorientation transition on a picosecond (ps) timescale due to the suppression of perpendicular magnetic anisotropy (PMA) and (ii) the PMA slowly restores, accompanied by out-of-plane magnetization recovery, leading to the generation of skyrmions with the help of spin fluctuations. This work provides a route to control skyrmion patterns using an fs laser, thereby establishing the foundation for further exploration of topological magnetism at ultrafast timescales.

Study of magnetic heterostructure MgO/CoFeB/Ta using the harmonic method

The heavy metal/ferromagnet type MgO/CoFeB/Ta structure with in-plane magnetization and high spin polarization was studied. We use the adiabatic harmonic Hall voltage method to study the effective damping coefficient and to estimate the values of the effective fields that arise in such structures under the action of a spin-polarized current.

Elucidating the superexchange mechanisms in magnetic coordination polymer [Co(HCOO)2(H2O)2]∞ through chemical bonding analysis

Single crystal synchrotron X-ray diffraction data are used to obtain an experimental electron density of a magnetic coordination polymer and thereby probe chemical interactions responsible for magnetic pathways.

Weyl nodal lines, Weyl points and the tunable quantum anomalous Hall effect in two-dimensional multiferroic metal oxynitride: Tl2NO2.

The investigation of two-dimensional (2D) multiferroic and topological quantum phases is a significant topic in current condensed matter physics. In this study, we discover quantum topological phases in the multiferroic material Tl2NO2. We observe that its ferroelectric (FE) phase displays a ferromagnetic ground state with magnetization favoring in-plane orientation. In the absence of spin-orbit coupling (SOC), a Weyl nodal loop around the Fermi level is evident, representing a 1D band crossing between spin-up and spin-down states. When spin-orbit coupling is taken into account, setting the magnetization in-plane, the Weyl nodal loop becomes gapped. Additionally, a pair of 2D Weyl nodes appear on the high-symmetry path, protected by a vertical mirror symmetry allowed by the magnetization. Remarkably, we prove that the Weyl nodes are situated at the topological phase transition between two quantum anomalous Hall (QAH) phases with opposite Chern numbers. Therefore, by adjusting the magnetization, it is possible to switch the propagation direction of chiral edge states. Furthermore, from its ferroelectric state to a paraelectric state, the time-reversal symmetry breaking nodal line is transformed into a Weyl point, achieving 100% spin polarization. Particularly, the Weyl points remain robust against SOC when the vertical mirror symmetry is preserved. Importantly, we also demonstrate that the Weyl point also represents the transition point where the QAH phase changes the sign of its Chern number. Overall, our study provides new insights into the study of multiferroic and topological phenomena in 2D materials and offers a potential avenue for controlling QAH phases.

Rashba Field Contribution and Electric Field Control of the Magnetic Anisotropy

"The anatomy of the Perpendicular Magnetic Anisotropy (PMA) in magnetic multilayered thin film heterostructures and the possibility to efficiently manipulate it by external electric fields represent major issues for technological applications in magnetic data storage devices. Solving a standard quantum model based on a Stoner-Rashba Hamiltonian, we illustrate that the magnetic properties in ultrathin magnetic films arise from the competing components identified in the magnetic energy: the Rashba correction to the Stoner splitting, a pseudo-dipolar contribution to the anisotropy energy proportional to the electric field at the interface that would favor in-plane magnetization configuration and a uniaxial-like perpendicular anisotropy term. This last term is responsible on the perpendicular magnetization configuration in ultrathin films and depends on the square of the electric field at the surface of the film. Investigating the time evolution of the magnetic system, we described the macrospin magnetization dynamics in terms of a Rashba field induced magnetization precession. Despite its simplicity, the quantum approach underlines the basic issues related to the physical origin and the mechanisms of the perpendicular magnetization in ultrathin magnetic films and illustrates the capability of manipulation by external gating electric field, in experiments similarly to Nuclear Magnetic Resonance. Keywords: perpendicular magnetic anisotropy, electric field control of anisotropy, magnetic tunnel junctions, magnetic multilayer heterostructures. "

Role of interfacial nickel silicides in shaping magnetic anisotropy in nickel films grown on Silicon substrates

Using different experimental techniques such as X-ray reflectivity, X-ray diffraction, X-ray photoelectron spectroscopy and magneto-optical Kerr effect (MOKE) microscopy, the structural and magnetic properties of Ni films grown on Si substrates are investigated. Various Ni-silicide phases are found to be formed at the Ni–Si interface as a function of depth following the sequence Ni-Ni2Si-NiSi-NiSi2 from the nickel to silicon side. This has been explained in terms of the effective heat of formation and inter-diffusion of the elements at the interface. In-plane magnetic anisotropy of the system is investigated by measuring in-plane magnetization using MOKE microscopy. The film exhibits an uniaxial in-plane magnetic anisotropy. An anomalous behavior, i.e., the collapse of the hard axis, has also been observed. This anomaly has been explained in terms of the creation of V-state domains during the magnetization reversal process at the hard axis. Interestingly, in-plane magnetic anisotropy could not be found in a Ni film grown with a Pt buffer layer on the Si substrate. Ni-silicide phases could not be detected in this system. This may suggests that the formation of silicides and diffusion at the interface causes the atypical magnetic anisotropy in Ni–Si sample.