Direction Of In-plane Magnetic Field Research Articles

Magnetism and magnetotransport in the kagome antiferromagnet Mn3Ge

We perform classical Monte Carlo and stochastic Landau-Lifshitz-Gilbert simulations to study the temperature-dependent magnetism of the kagome antiferromagnet Weyl metal ${\text{Mn}}_{3}\text{Ge}$, and we find that a long-range chiral order sets in at a transition temperature well below the N\'eel temperature (${T}_{N}$). Based on the crystalline symmetries imposed by the chiral magnetic order, we argue for the presence of multiple isoenergetic Weyl nodes (nodes that are at the same energy and with a congruent Fermi surface around them) near the chemical potential. Using the semiclassical Boltzmann equations, we show that the combined contribution to the net longitudinal magnetoconductance (LMC) and the planar Hall conductance (PHC) from tilted Weyl nodes can lead to signatures that are qualitatively distinct from that of a single pair of Weyl nodes. In particular, we show that magnetic orders with different chiralities can give rise to different periods in LMC and PHC as a function of the in-plane magnetic field direction. This is ultimately related to differences in the symmetry-imposed constraints on the Weyl nodes.

Anisotropic terahertz transmission induced by the external magnetic field in La0.67Ca0.33MnO3 film.

A systemic investigation of the terahertz (THz) transmission of La0.67Ca0.33MnO3 film on the (001)-oriented NdGaO3 substrate under external magnetic field and low temperature have been performed. The significant THz absorption difference between the out-of-plane and the in-plane magnetic field direction is observed, which is consistent with the electrical transport measurement using the standard four-probe technique. Furthermore, we find that the complex THz conductivities can be reproduced in terms of the Drude Smith equation as the magnetic field is perpendicular to the film plane, whereas it deviates from this model when the in-plane magnetic field is applied. We suggest that such anisotropies in THz transport dynamics have close correspondences with the phase separation and anisotropic magnetoresistance effects in the perovskite-structured manganites. Our work demonstrates that the THz time-domain spectroscopy (TDS) can be an effective non-contact method for studying the magneto-transport properties of the perovskite-structured manganites.

Anisotropic Magnon–Magnon Coupling in Synthetic AntiferromagnetsSupported by the National Natural Science Foundation of China (Grant Nos. 51871235, 51671212, 52031014, 51771198, and 51801212), the National Key Research and Development Program of China (Grant Nos. 2016YFA0300701, 2017YFB0702702, and 2017YA0206302), and the Key Research Program of Frontier Sciences, CAS (Grant Nos. QYZDJ-SSW-JSC023, KJZD-SW-M01, and ZDYZ2012-2). J.L. acknowledges support from the Natural Science Foundation

Magnon–magnon coupling in synthetic antiferromagnets advances it as hybrid magnonic systems to explore the quantum information technologies. To induce magnon–magnon coupling, the parity symmetry between two magnetization needs to be broken. Here we experimentally demonstrate a convenient method to break the parity symmetry by the asymmetric structure. We successfully introduce a magnon–magnon coupling in Ir-based synthetic antiferromagnets CoFeB(10 nm)/Ir(t Ir = 0.6 nm, 1.2 nm)/CoFeB(13 nm). Remarkably, we find that the weakly uniaxial anisotropy field (∼ 20 Oe) makes the magnon–magnon coupling anisotropic. The coupling strength presented by a characteristic anticrossing gap varies in the range between 0.54 GHz and 0.90 GHz for t Ir = 0.6 nm, and between 0.09 GHz and 1.4 GHz for t Ir = 1.2 nm. Our results demonstrate a feasible way to induce magnon–magnon coupling by an asymmetric structure and tune the coupling strength by varying the direction of in-plane magnetic field. The magnon–magnon coupling in this highly tunable material system could open exciting perspectives for exploring quantum-mechanical coupling phenomena.

Independent Control of the Chirality and Polarity for the Magnetic Vortex in Symmetric Nanodot Pairs

We studied the vortex states during the magnetization process for nanomagnetic dot pairs in different geometries, including a series of dual regular polygons with 4–16 sides and irregular shape dot pairs. All geometries demonstrated independent control of the vortex chirality and polarity and could be accomplished by adjusting the in-plane magnetic field direction. To achieve chirality and polarity control, both shape anisotropy and coupling interaction play a vital role. For the regular polygons, the effect of shape anisotropy wanes as the number of side increases, and the coupled interaction is enhanced relatively. According to the results, and combined with those for dual-circle and dual-rectangular magnetic disks, we state the principle for the geometry of the disk to achieve independent control of the chirality and polarity.

Out-of-plane electric polarization in double-fan magnetic phase of Y-type hexaferrite

It has been revealed that a Y-type hexaferrite ${\mathrm{BaSrCo}}_{2}{\mathrm{Fe}}_{11.1}{\mathrm{Al}}_{0.9}{\mathrm{O}}_{22}$ hosts not only an in-plane $({P}_{ab})$ but also an out-of-plane $({P}_{c})$ component of magnetically induced electric polarization in the double-fan magnetic phase. With an increasing in-plane magnetic field, the magnitude of ${P}_{c}$ reaches a maximum at around $2\phantom{\rule{0.28em}{0ex}}\text{T}$ and decreases as approaching the critical field $(3.8\phantom{\rule{0.28em}{0ex}}\text{T})$ of the transition to the collinear ferrimagnetic phase. ${P}_{c}$ has also been verified to show a ${120}^{\ensuremath{\circ}}$-period oscillation as a function of the in-plane magnetic field direction. These results are reproduced by a model combining the inverse Dzyaloshinskii-Moriya interaction and the spin-dependent $pd$ hybridization mechanisms.

Topological Larkin-Ovchinnikov phase and Majorana zero mode chain in bilayer superconducting topological insulator films

Topological superconductors possess a bulk superconducting gap and boundary gapless excitations, known as “Majorana fermion”. Search for new systems with topological superconductivity is of fundamental and application importance due to the potential application of Majorana fermions in topological quantum computation. Here we show that the Larkin-Ovchinnikov superconducting phase with a finite momentum pairing can emerge in a model of bilayer superconducting topological insulator films, in which superconductivity appears for both the top and bottom surface states, and can be topologically non-trivial. This “topological Larkin-Ovchinnikov phase” is induced by an in-plane magnetic field and possesses a Majorana mode chain along the edge perpendicular to the in-plane magnetic field direction due to its non-trivial {Bbb Z}_2 topological nature. Our theoretical model can be naturally realized in superconductor/topological insulator sandwich structure or in Fe(Te, Se) film, a topological material with superconductivity, and thus provides a route to explore unconventional superconductivity in existing systems.

Weak antilocalization induced by Rashba spin-orbit interaction in layered III-VI compound semiconductor GaSe thin films

Magnetoconductance (MC) at low temperature was measured to investigate spin-related transport affected by spin-orbit interaction (SOI) in III-VI compound $n$-type GaSe thin films. Results reveal that MC shows weak antilocalization (WAL). Its temperature and gate voltage dependences reveal that the dominant spin relaxation is governed by the D'yakonov-Perel' mechanism associated with the Rashba SOI. The estimated Rashba SOI strength in GaSe is much stronger than that of III-V compound GaAs quantum wells, although the energy gap and spin split-off band in GaSe closely resemble those in GaAs. The angle dependence of WAL amplitude in the in-plane magnetic field direction is almost isotropic. This isotropy indicates that the strength of the Dresselhaus SOI is negligible compared with the Rashba SOI strength. The SOI effect in $n$-GaSe thin films differs greatly from those of III-V compound semiconductors and transition-metal dichalcogenides.

Independent control of the vortex chirality and polarity in a pair of magnetic nanodots

Independent control of the vortex chirality and polarity is realized by changing the in-plane magnetic field direction in nanodot pair through Object Oriented Micromagnetic Framework (OOMMF) simulation. The two magnetic circles are close to each other and have magnetic interaction. The two circles always have the same polarity and opposite chirality at every remanent state. There are totally four predictable magnetic states in the nanodot pair which can be obtained in the remanent state relaxed from the saturation state along all possible directions. An explanation on the formation of vortex states is given by vortex dynamics. The vortex states are stable in large out-of-plane magnetic field which is in a direction opposite to the vortex polarity. The geometry of the nanodot pair gives a way to easily realize a vortex state with specific polarity and chirality.

TRANSPORT PROPERTIES OF A SUPERCONDUCTING FILM WITH MAGNETIC NANOSTRIPES

Studies of the transport properties of a Sn superconducting film with several (1–7) parallel nickel magnetic nanostripes deposited on the top of a thin Ge insulating layer covering the surface of the superconducting film are reported. Measurements of the dependence of the resistance on the in-plane magnetic field with two magnetic field orientations (parallel to the stripes direction and perpendicular to the stripes) and the temperature have been made. We have studied resistance versus in-plane magnetic field direction. Different types of strong hysteresis in the resistance dependence on the magnetic field for different magnetic field orientations were observed.

Magnetoresistance studies of MeV ranged 1H+ and 12C+ ion irradiated HOPG flakes

2MeV protons and 1MeV carbon ions are bombarded on highly oriented pyrolytic graphite (HOPG) samples and their electronic transport measurements are carried out in the presence of magnetic field. The Magneto-Resistance (MR) measurements show measurable hysteresis in the resistance value after ion beam irradiation for the in-plane magnetic field direction as well as for the out-of-plane field direction. The MR depends on the thickness of the flake and the method of its separation from the bulk HOPG. The results substantiate that the ferromagnetic coupling between the magnetic moments at the vacancy defect sites in HOPG sensitively depends on the average defect separation. The average defect separation range of 1.7–0.5nm allows only a part of the 40μm thick proton beam irradiated sample to go for ferromagnetic ordering. Similar conclusions are drawn from carbon ion irradiated HOPG flake. The irradiation increases the resistance of the flake as well.

Giant reversible anisotropic magnetocaloric effect in an antiferromagnetic EuFe2As2 single crystal

Here, we report the characterization of a giant reversible anisotropic magnetocaloric effect in a EuFe2As2 single crystal. The magnetic properties of EuFe2As2 single crystals are quite interesting; they display a small magnetic hysteresis, anisotropy, and a first-order magnetic phase transition. The maximum magnetic entropy change in in-plane magnetic-field direction was 14.6 J/kg K around 20 K and out-of-plane was 10.3 J/kg K around 20 K as a result of changing the magnetic field from 0 to 5 T. These results suggest the possibility of using EuFe2As2 single crystals in magnetic refrigeration applications.

MFM analysis of magnetic inhomogeneity in recorded area for perpendicular magnetic recording media by simultaneous imaging of perpendicular and in-plane magnetic field gradient

A new MFM method which can measure the perpendicular and in-plane magnetic field gradient simultaneously was developed. The measuring direction of in-plane magnetic field can be easily changed only by selecting the scanning direction of MFM tip with respect to the sample. This method was used to successfully estimate the magnetic domain structure of recorded area on CoCrPt-SiO2 perpendicular magnetic recording media. When the scanning direction is along the down-track direction, the component of strong magnetic field gradient along the down-track direction can be observed with high spatial resolution at the bit transition. On the other hand, when the scanning direction is along the corss-track direction, the new MFM method is effective to mask the component of magnetic field from homogeneous recorded bits, and consequently the components of magnetic field from bended recorded bits at the track edge can be observed. The simultaneous measurement of perpendicular and in-plane magnetic field is useful to evaluate the magnetic inhomogeneity of recorded area such as bit transition and track edge.

Anisotropic structure of the order parameter in FeSe(0.45)Te(0.55) revealed by angle-resolved specific heat.

The central issues for understanding iron (Fe)-based superconductors are the symmetry and structure of the superconducting gap. So far the experimental data and theoretical models have been highly controversial. Some experiments favor two or more constant or nearly constant gaps, others indicate strong anisotropy and yet others suggest gap zeros ('nodes'). A unique method for addressing this issue, and one of very few methods that are bulk and angle resolved, is measuring the electronic-specific heat in a rotating magnetic field. In this study, we present the first such measurement for an Fe-based high-Tc superconductor. We observed a fourfold oscillation of the specific heat as a function of the in-plane magnetic field direction. Our results are consistent with the expectations for an extended s-wave model, with a significant gap anisotropy on the electron pockets and the gap minima along the ΓM (Fe–Fe bond) direction.

ν=5/2Fractional Quantum Hall Effect at 10 T: Implications for the Pfaffian State

We report on the magnetotransport (including tilt fields) around Landau level filling factor nu=5/2 in a high-purity modulation-doped GaAs/AlGaAs quantum well with twice the electron density of standard samples. A quantized 5/2 Hall plateau is observed at B approximately = 10 T, with an activation gap approximately 125 mK; the plateau can persist up to approximately 25 degree tilt field. This finding is discussed in the context of a proposed Moore-Read Pfaffian (or anti-Pfaffian) wave function being a possible ground state at 5/2. The tilt fields induce a background resistance at 5/2 that could be either isotropic or anisotropic, depending simply on the in-plane magnetic field direction with respect to the GaAs crystalline axis. Such data indicate a substantial coupling between the 5/2 collective phases and the GaAs crystal.

Effects of in-plane magnetic field direction on the nuclear-spin relaxation in the [formula omitted] quantum Hall state

We investigated effects of the direction of in-plane magnetic field B ∥ on the phase transition in the quantum Hall ferromagnet at Landau-level filling factor ν = 2 3 by the nuclear-spin relaxation measurements. We controlled the angle φ between the direction of B ∥ and a current I; when B ∥ is parallel (perpendicular) to I, φ = 0 ∘ ( φ = 90 ∘ ) . We found that the nuclear spin relaxation rate T 1 - 1 at φ = 0 ∘ is about twice as much as that at φ = 90 ∘ . We discuss the anisotropic behavior of T 1 - 1 in term of a suppression of low-frequency electron spin fluctuations by B ∥ at φ = 90 ∘ .

Low temperature magnetic and transport anisotropy in Pr0.7Sr0.3MnO3: The magnetostriction scenario

Angle-resolved magnetic and transport measurements of a Pr0.7Sr0.3MnO3 thin film as a function of the in-plane magnetic field direction are discussed. The origins of the anisotropic magnetotransport evidenced near Curie temperature and at T=30 K are shown to strongly differ. Quantitative magnetic simulations of the angular dependence of the magnetization at T=30 K were used to evaluate the anisotropy energy in low field. A rotation of the in-plane easy axis induced by high fields at T=30 K is attributed to the magnetostriction caused by the praseodymium ions. Furthermore, a model taking into account this plausible magnetostrictive effect is shown to qualitatively reproduce the observed low temperature transport anisotropy.