In-plane Magnetic Field Research Articles

Two types of superconducting pairs in stripe-ordered La2−xBaxCuO4 (x=1/8) : Evidence from resistivity measurements

Recent angle-resolved $c$-axis resistivity measurements of the stripe-ordered ${\mathrm{La}}_{2\ensuremath{-}x}{\mathrm{Ba}}_{x}{\mathrm{CuO}}_{4}$ (LBCO) with $x=1/8$ revealed an unexpected dependence on the direction of the in-plane magnetic field. We argue that these and other available data for the $c$-axis transport point to the existence of superconducting pairs of two different types in the $x=1/8$ LBCO below the stripe ordering temperature. The pairs of one type carry finite momentum and are confined to the Cu-O planes; the pairs of other type (probably the conventional $d$ wave with zero momentum) propagate along narrow conducting channels traversing the sample in the $c$-axis direction. The evidence for this comes from the observed exponential temperature dependence of the $c$-axis resistivity ${\ensuremath{\rho}}_{c}(T)$ which we attribute to the thermally excited slips of the superconducting phase and flux flows. We present a simple theory to fit the observed $\ensuremath{\pi}/2$-periodic dependence of ${\ensuremath{\rho}}_{c}$ on the direction of the in-plane magnetic field and the other data.

Kondo screening of single magnetic impurity doped type-II Ising superconductors

We theoretically study the Kondo effect in type-II Ising superconductors with a single magnetic impurity. Type-II Ising superconductivity was found in two-dimensional centrosymmetric materials with multiple degenerate orbitals, such as in few-layer stanene [Falson et al., Science 367, 1454 (2020)] and ultrathin ${\mathrm{PdTe}}_{2}$ films [Liu et al., Nano Lett. 20, 5728 (2020)]. The type-II Ising spin-orbit coupling (SOC) in these materials generates out-of-plane effective Zeeman fields orienting opposite directions for opposing orbitals, which strongly protects the interorbital superconducting pairing states against in-plane magnetic fields. We show that the SOC-induced band splitting and the chemical potential significantly influence the formation of a localized magnetic moment, with particle-hole asymmetry in the phase boundary between magnetic and nonmagnetic states. The behaviors of spin-induced Yu-Shiba-Rusinov bound states and low-temperature magnetic susceptibility demonstrate that the SOC suppresses the Kondo screening of the magnetic moment, while the interorbital mixing weakens the SOC at finite momentum, then enhances the Kondo effect. The quantum phase transition between magnetic doublet and Kondo singlet ground states can be tuned through chemical potential in experiments.

Temperature dependent intrinsic Gilbert damping in magnetostrictive FeCoSiB thin film

A low Gilbert damping factor is crucial for emerging magneto-acoustic devices. In current work, angle-dependent and temperature-dependent Gilbert damping of magnetostrictive FeCoSiB thin films have been investigated using electron spin resonance (ESR) and vector network analyzer ferromagnetic resonance (VNA-FMR) techniques, respectively. A very low Gilbert damping factor ∼0.0038 was measured with in-plane magnetic fields at room temperature. Temperature-dependent VNA-FMR results between 10 K and 300 K exhibit a conductivity-like damping feature, which can be attributed to the spin-orbital coupling dominantly controlled by the intraband scattering. Our results clearly indicate that highly magnetostrictive or piezomagnetic film does not necessarily have a high intrinsic damping factor.

Engineering structured magnetic bits for magnonic holographic memory

Magnonic holographic memory is a type of memory that uses spin waves for magnetic bit read-in and read-out. Its operation is based on the interaction between magnets and propagating spin waves where the phase and the amplitude of the spin wave are sensitive to the magnetic field produced by the magnet. Memory states 0 and 1 are associated with the presence/absence of the magnet in a specific location. In this work, we present experimental data showing the feasibility of magnetic bit location using spin waves. The testbed consists of four micro-antennas covered by Y3Fe2(FeO4)3 yttrium iron garnet (YIG) film. A constant in-plane bias magnetic field is provided by NdFeB permanent magnet. The magnetic bit is made of strips of magnetic steel to maximize interaction with propagating spin waves. In the first set of experiments, the position of the bit was concluded by the change produced in the transmittance between two antennas. The minima appear at different frequencies and show different depths for different positions of the bit. In the second set of experiments, two input spin waves were generated, where the phase difference between the waves is controlled by the phase shifter. The minima in the transmitted spectra appear at different phases for different positions of magnetic bit. The utilization of the structured bit enhances its interaction with propagating spin waves and improves recognition fidelity compared to a regular-shaped bit. The recognition accuracy is further improved by exploiting spin wave interference. The depth of the transmission minima corresponding to different magnet positions may exceed 30 dB. All experiments are accomplished at room temperature. Overall, the presented data demonstrate the practical feasibility of using spin waves for magnetic bit red-out. The practical challenges are also discussed.

Stability of line-node semimetals with strong Coulomb interactions and properties of the symmetry-broken state

We study the stability and phenomenology of line-node semimetals in the presence of Coulomb interactions. Our results indicate a phase transition to a chiral insulating state that occurs at a finite interaction threshold, which we determine. We also compute the Landau levels for out-of-plane and in-plane magnetic fields in the symmetric and symmetry-broken phases. We find that the magnetic field couples to the chiral order parameter, implying that this degree of freedom can be manipulated in situ in experiments. Finally, we check the existence of edge states in the symmetry-broken phase. On the system's boundary, we note that the metallic ``drum-head'' states that exist in the symmetric phase are gapped out. However, the symmetry-broken phase permits topological defects in the macroscopic order parameter in the form of domain walls, which host metallic ``interface states.'' These consist of linelike gap-closings that occur on the two-dimensional interfaces.

Perspectives on field-free spin–orbit torque devices for memory and computing applications

The emergence of embedded magnetic random-access memory (MRAM) and its integration in mainstream semiconductor manufacturing technology have created an unprecedented opportunity for engineering computing systems with improved performance, energy efficiency, lower cost, and unconventional computing capabilities. While the initial interest in the existing generation of MRAM—which is based on the spin-transfer torque (STT) effect in ferromagnetic tunnel junctions—was driven by its nonvolatile data retention and lower cost of integration compared to embedded Flash (eFlash), the focus of MRAM research and development efforts is increasingly shifting toward alternative write mechanisms (beyond STT) and new materials (beyond ferromagnets) in recent years. This has been driven by the need for better speed vs density and speed vs endurance trade-offs to make MRAM applicable to a wider range of memory markets, as well as to utilize the potential of MRAM in various unconventional computing architectures that utilize the physics of nanoscale magnets. In this Perspective, we offer an overview of spin–orbit torque (SOT) as one of these beyond-STT write mechanisms for the MRAM devices. We discuss, specifically, the progress in developing SOT-MRAM devices with perpendicular magnetization. Starting from basic symmetry considerations, we discuss the requirement for an in-plane bias magnetic field which has hindered progress in developing practical SOT-MRAM devices. We then discuss several approaches based on structural, magnetic, and chiral symmetry-breaking that have been explored to overcome this limitation and realize bias-field-free SOT-MRAM devices with perpendicular magnetization. We also review the corresponding material- and device-level challenges in each case. We then present a perspective of the potential of these devices for computing and security applications beyond their use in the conventional memory hierarchy.

Fabrication and performance evaluation of magnetically driven double curved conical ribbon micro-helical robot

In this research, a magnetically driven double curved conical ribbon micro-helical robot was proposed to improve the swimming stability and swimming performance. Its swimming performance as well as magnetization characteristics were analyzed by fluid dynamics simulation. Meanwhile, a transverse bidirectional fold-line scanning method was proposed to fabricate the designed microrobots via voxel-modulation two-photon polymerization microfabrication technology. After optimizing the machining parameters, the length dimension error of the double curved conical ribbon micro-helical robot could be further reduced to less than 1%. Furthermore, a conical rotating three-dimensional uniform magnetic field was established to drive the microrobots. Microrobot driven experiment of the conical rotating three-dimensional uniform magnetic field was conducted and compared with the planar uniform magnetic field. It is proved that the micro-helical robot driven by the conical rotating three-dimensional uniform magnetic field can achieve high stability and no swing swimming in the low-frequency spiral propulsion state. This work may provide a reference for the future application of micro-helical robots in the fields of drug delivery, cell sorting, sensing and environmental repair in vivo.

Y-type hexagonal ferrite-based band-pass filter with dual magnetic and electric field tunability

This work is on the design, fabrication and characterization of a hexagonal ferrite band-pass filter that can be tuned either with a magnetic field or an electric field. The filter operation is based on a straight-edge Y-type hexagonal ferrite resonator symmetrically coupled to the input and output microstrip transmission lines. The Zn2Yfilter demonstrated magnetic field tunability in the 8–12 GHz frequency range by applying an in-plane bias magnetic field H0 provided by a built-in permanent magnet. The insertion loss and 3 dB bandwidth within this band were 8.6 ± 0.4 dB and 350 ± 40 MHz, respectively. The electric field E tunability of the pass-band of the device was facilitated by the nonlinear magnetoelectric effect (NLME) in the ferrite. The E-tuning of the center frequency of the filter by (1150 ± 90) MHz was obtained for an input DC electric power of 200 mW. With efforts directed at a significant reduction in the insertion loss, the compact and power efficient magnetic and electric field tunable Zn2Y band-pass filter has the potential for use in novel reconfigurable RF/microwave devices and communication systems.

En route to next-generation nerve repair: static passive magnetostimulation modulates neurite outgrowth

Objective. Regeneration of damaged nerves is required for recovery following nervous system injury. While neural cell behavior may be modified by neuromodulation techniques, the impact of static direct current (DC) magnetic stimulation remains unclear. Approach. This study quantifies the effects of DC magnetostimulation on primary neuronal outgrowth in vitro. The extension of neurites of dorsal root ganglia (DRG) subjected to two different low-strength (mT) static magnetic flux configurations was investigated. Main results. After 3 d of 1 h in-plane (IP) magnetic field stimulation, a 62.5% increase in neurite outgrowth area was seen relative to unstimulated controls. The combined action of in-plane + out-of-plane (IP + OOP) magnetic field application produced a directional outgrowth bias parallel to the IP field direction. At the same time, the diverse magnetic field conditions produced no changes in two soluble neurotrophic factors, nerve growth factor and brain-derived neurotrophic factor, released from resident glia. Significance. These results demonstrate the potential for DC magnetostimulation to enhance neuronal regrowth and improve clinical outcomes.

Robot-Aided Magnetic Navigation System for Wireless Capsule Manipulation

Magnetic navigation systems (MNSs) have been developed to use in the diagnosis of gastrointestinal problems. However, most conventional magnetic navigation systems are expensive and have structural problems because of their large weights and volumes. Therefore, this paper proposes C-Mag, a novel compact MNS composed of two electromagnets and a robotic arm. The two electromagnets generate a planar magnetic field, and the robotic arm rotates and translates the electromagnets to manipulate the magnetic capsule in a large 3-dimensional (3-D) space. The C-Mag design considers the payload of the robotic arm and the capacity of the power supply unit. Under these limited conditions, the C-Mag was optimized to generate the maximum magnetic field considering several major factors. Finally, the C-Mag was constructed, and the maximum magnetic field that could be generated in one direction was 18.65 mT in the downward direction. Additionally, the maximum rotating magnetic field was 13.21 mT, which was used to manipulate the capsule. The performance was verified by measuring the generated magnetic field, and it matched well with the simulated result. Additionally, the path-following experiment of the magnetic capsule showed that the proposed C-Mag can effectively manipulate the magnetic capsule in 3-D space using the robotic arm. This study is expected to contribute to the further development of magnetic navigation systems to treat gastrointestinal problems.

Field-free spin-orbit torque switching of GdCo ferrimagnet with broken lateral symmetry by He ion irradiation

Current-induced magnetization switching by spin-orbit torque (SOT) is of great importance for the energy-efficient operation of spin-based memory and logic devices. However, the requirement of an external in-plane magnetic field to deterministically switch the perpendicular magnetization of a device is a bottleneck for device application. There have been many efforts to realize field-free SOT switching using interlayer/exchange coupling, the spin valve structure, or materials with lateral symmetry breaking. However, limitations of material selection or layer structure modification hinder the application of these methods in practice. Here, we demonstrate the field-free SOT switching of a GdCo ferrimagnet with lateral symmetry breaking by He ion irradiation. Local control of the magnetic property with different He ion irradiation conditions induces a lateral magnetic gradient orthogonal to the current flow direction in the ferrimagnet. We also observe out-of-plane-SOT generation due to lateral symmetry breaking, which is essential for field-free switching. Since the He ion irradiation technique is utilized for the fabrication of complementary−metal−oxide−semiconductors, and resolution can reach the nanometer level, our findings have the potential to serve as the basis for new developments in the fabrication of wafer-scale spintronic memory and logic devices with high energy efficiency and high density.

Altshuler-Aronov-Spivak interference of one-dimensional helical edge states in MoTe2

Recent theories predicted that $1{\mathrm{T}}^{\ensuremath{'}}\text{\ensuremath{-}}\mathrm{MoT}{\mathrm{e}}_{2}$ is a higher-order topological insulator (HOTI) exhibiting one-dimensional (1D) conducting edge states, and that ${\mathrm{T}}_{d}\text{\ensuremath{-}}\mathrm{MoT}{\mathrm{e}}_{2}$ becomes a HOTI with broken inversion symmetry under strain or lattice distortion. Here, we report the transport evidence for 1D helical edge states in ${\mathrm{MoTe}}_{2}$ thin flakes. Under an in-plane magnetic field perpendicular to the current, Altshuler-Aronov-Spivak interference of edge states is observed, in which the oscillating period corresponding to magnetic flux $h/2e$ agrees with the lateral cross-sectional area. The absence of Aharonov-Bohm interference stems from the helical nature of the edge states. Temperature evolution of the fast Fourier transform amplitude is further obtained, indicating the quasiballistic transport mode. Our work deepens the understanding of higher-order topological properties of ${\mathrm{MoTe}}_{2}$, paving the way for further topological electronics.

Enhanced superconductivity in spin-orbit proximitized bilayer graphene.

In the presence of a large perpendicular electric field, Bernal-stacked bilayer graphene (BLG) features several broken-symmetry metallic phases1-3 as well as magnetic-field-induced superconductivity1. The superconducting state is quite fragile, however, appearing only in a narrow window of density and with a maximum critical temperature Tc ≈ 30 mK. Here we show that placing monolayer tungsten diselenide (WSe2) on BLG promotes Cooper pairing to an extraordinary degree: superconductivity appears at zero magnetic field, exhibits an order of magnitude enhancement in Tc and occurs over a density range that is wider by a factor of eight. By mapping quantum oscillations in BLG-WSe2 as a function of electric field and doping, we establish that superconductivity emerges throughout a region for which the normal state is polarized, with two out of four spin-valley flavours predominantly populated. In-plane magnetic field measurements further reveal that superconductivity in BLG-WSe2 can exhibit striking dependence of the critical field on doping, with the Chandrasekhar-Clogston (Pauli) limit roughly obeyed on one end of the superconducting dome, yet sharply violated on the other. Moreover, the superconductivity arises only for perpendicular electric fields that push BLG hole wavefunctions towards WSe2, indicating that proximity-induced (Ising) spin-orbit coupling plays a key role in stabilizing the pairing. Our results pave the way for engineering robust, highly tunable and ultra-clean graphene-based superconductors.

Higher-order oscillatory planar Hall effect in topological kagome metal

Exploration of exotic transport behavior for quantum materials is of great interest and importance for revealing exotic orders to bring new physics. In this work, we report the observation of unconventional prominent planar Hall effect (PHE) and planar anisotropic magnetoresistivity (PAMR) in strange kagome metal KV3Sb5. The PHE and PAMR, which are driven by an in-plane magnetic field and display sharp difference from other Hall effects driven by an out-of-plane magnetic field or magnetization, exhibit exotic higher-order oscillations in sharp contrast to those following empirical rule only allowing two-fold symmetrical oscillations. These higher-order oscillations exhibit strong field and temperature dependence and vanish around charge density wave (CDW) transition. The unique transport properties suggest a significant interplay of the lattice, magnetic and electronic structure in KV3Sb5. This interplay can couple the hidden anisotropy and transport electrons leading to the unconventional PHE and PAMR in contrast to other materials.

Dzyaloshinskii-Moriya-Interaction-Like Behavior in Confined Permalloy Nanostructures via Coupled Magnetic Vortices.

Dzyaloshinskii-Moriya interaction (DMI), one of antisymmetric exchanges, originates from the combination of low structural symmetry and large spin-orbit coupling and favors magnetization rotations with fixed chirality. Herein, this work reports a DMI-like behavior in permalloy via coupled vortices in confined structures. Under the in-plane magnetic fields, continuous reversals of different coupled vortices are directly observed by in situ Lorentz transmission electron microscopy, and reproduced by complementary micromagnetic simulations. The statistical results show that coupled vortices with opposite chirality appear more frequently with the frequency up to about 60%. Such an asymmetric phenomenon mainly arises from a DMI-like behavior, associated with the increased total energy difference between different ground-state coupled vortices. Moreover, in the reversal process, the junction between disks accelerates the annihilation of vortices moving toward it and is also the starting point of vortex nucleation. These results provide an effective method to generate a DMI-like behavior in magnetic systems with symmetry breaking surface and benefit the future development of vortex-based spintronic devices.

The In-Plane Magnetic Field Measurement Method of SC/MR Mixed Sensor and Its Three-Axis Magnetic Sensor With Integrated Magnetic Concentrator

Superconductor/magnetoresistance (SC/MR) mixed sensor has the advantage of ultrahigh sensitivity and is thought to be a promising candidate for weak magnetic field detection. However, it has no effect on the magnetic field in the superconducting flux-to-field transformation amplifier (SFTA) plane, which limits its applications in 3-D magnetic field detection. Here, we present a new architecture of SC/MR mixed sensor with only one integrated magnetic concentrator (IMC) to realize the in-plane magnetic field measurement. Firstly, the conversion efficiency, defined as the in-plane magnetic changing to the out-plane magnetic field by the IMC and SFTA of mixed sensor, was systematically studied by the finite element analysis method, the results show that the high conversion efficiency is from the combined action of superconducting diamagnetism and magnetic concentrator of soft magnetic materials. Then, a serial prototype mixed sensors with different IMC relative configuration sizes were prepared and their experimental performances were obtained. Indeed, the mixed sensor with IMC can simultaneously measure the in-plane and out-of-plane magnetic fields, furthermore, the conversion efficiency changes as the function of the relative configuration size is consistent well with the simulation result. Finally, a three-axis SC/MR mixed sensor scheme and its corresponding three-axis magnetic field decoupling method based on this method were also proposed, showing the obvious capability of three-axis magnetic field measurement. Our work is meaningful to the development of a three-axis weak magnetic field detection.

Instability of skyrmion lattice under microwave magnetic field due to single-q helimagnetic excitation mode

Composed of the three spiral magnetic vectors, the structure of skyrmion lattice (SkL) can be destructed by spin excitations in possibly two ways: one is to make decoherence of all the helices through the phase change of a certain spiral magnetic vector, and the other is to inhibit one or two spiral components while enhancing the others so that it becomes a magnetic structure of single or double magnetic vectors. Here, we present a micromagnetic study on the spin excitations of a two-dimensional SkL under the in-plane microwave magnetic field. By calculating the parameters describing the in-plane spin excitations mode, we find that the spin configuration tends to be an enhanced single-vector spiral magnetic structure due to the excitation modes under some specific frequencies so that the SkL will collapse to the topologically trivial state. Our results help to form a deeper understanding of the spin excitation in SkL under an ac magnetic field.

Quantum nonlinear planar Hall effect in bilayer graphene: An orbital effect of a steady in-plane magnetic field

We study the quantum nonlinear planar Hall effect in bilayer graphene under a steady in-plane magnetic field. When time-reversal symmetry is broken by the magnetic field, a charge current occurs in the second-order response to an external electric field as a result of the Berry curvature dipole in momentum space. We show that a nonlinear planar Hall effect originating from the anomalous velocity is caused by an orbital effect of an in-plane magnetic field on electrons in bilayer graphene in the complete absence of spin-orbit coupling. Taking into account the symmetry analysis, we derive the dominant dependence of the Berry curvature dipole moment on the magnetic field components. Moreover, we illustrate how to control and modulate the Berry curvature dipole with an external planar magnetic field, gate voltage, and Fermi energy.

Magnetotransport as a probe for the interplay between Sm and Fe magnetism in SmFeAsO

The complex magnetic ordering of parent compounds of most unconventional superconductors is crucial for the understanding of high-temperature superconductivity (SC). Within this framework, we have performed temperature-dependent magnetotransport experiments on a single crystal of SmFeAsO, a parent compound of iron pnictide superconductors. We observe multiple features in the measured transport properties at temperatures below the antiferromagnetic (AFM) ordering of Sm, , which evolve with in-plane magnetic field, suggesting a rich variety of metamagnetic transitions never before observed in this compound. Considering that transport mainly involves Fe d orbitals at the Fermi level, these findings suggest that the features originate from magnetic transitions of the Fe moments sublattice, which in turn may be induced by magnetic transitions of the Sm moments sublattice via the interaction between Fe and Sm moments. We outline a possible scenario in which the Fe moments, strongly affected by the Sm ordering below T NSm, reorder to an in-plane canted AFM structure, which is washed out by the application of an in-plane magnetic field up to 9 T. Our work shows that transport properties are a valuable tool for investigating magnetic ordering in iron pnictide parent compounds, where the interplay of magnetism and SC is believed to be the origin of high-temperature SC.

Evidence for a Phase Transition in the Quantum Spin Liquid State of a Kitaev Candidate α-RuCl3

The Kitaev quantum spin liquid (QSL) on the two-dimensional honeycomb lattice epitomizes an entangled topological state, where the spins fractionalize into Majorana fermions. This state has aroused tremendous interest because it harbors non-Abelian anyon excitations. The half-integer quantized thermal Hall (HIQTH) conductance observed in $\alpha$-RuCl$_3$ is a key signature of these excitations. However, the fate of this topologically nontrivial state at intense fields remains largely elusive. Here, we report the thermal conductivity $\kappa$ and specific heat $C$ of $\alpha$-RuCl$_3$ with in-plane magnetic fields $H$. For the field direction perpendicular to the Ru-Ru bond, where the HIQTH effect is observed, we find a discontinuous jump in $\kappa(H)$ and a peak anomaly in $C(H)$ at $\mu_0H^*\approx11$\,T, evidencing a weak first-order phase transition. Remarkably, the HIQTH effect vanishes close to $H^*$. Furthermore, we find that the spin-fractionalization feature is retained well above $H^\ast$. These imply the emergence of the phase transition that separates two QSL phases with distinct topological properties.