Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session W41: Transport Phenomena of Spin Textures |
Hide Abstracts |
Sponsoring Units: GMAG DMP Chair: Nikolai S. Kiselev Room: 707 |
Friday, March 6, 2020 8:00AM - 8:12AM |
W41.00001: Evidence of Topological Hall Effect in Pt/Antiferromagnetic-Insulator Bilayers Yang Cheng, Sisheng Yu, Menglin Zhu, Jinwoo Hwang, Fengyuan Yang Topological Hall effect has been a primary indicator of spin textures in magnetic materials. We observe unambiguous the evidence of topological Hall effect in Pt/Cr2O3 bilayers grown on Al2O3(0001) and Al2O3(11-20), where Cr2O3 epitaxial film is an antiferromagnetic insulator. The Pt/Cr2O3 bilayers exhibit clear topological Hall resistivity for Cr2O3 thicknesses below 6 nm near and above room temperature, which is above the Néel temperature of Cr2O3, revealing the key role of thermal fluctuations in the formation of spin textures. The similarity of topological Hall signals in (0001) and (11-20)-oriented Cr2O3 films indicates that the emergence of spin textures is insensitive to crystalline orientation. This first observational evidence of topological Hall effect in HM/AFI bilayers significantly expands our materials base to include the large family of AF insulators for the exploration of AF-based skyrmion technology. |
Friday, March 6, 2020 8:12AM - 8:24AM |
W41.00002: Control of ferromagnetic Curie temperature and topological Hall effect in chromium telluride thin films In Hak Lee, Byoung Ki Choi, Hyuk Jin Kim, Min Jae Kim, Kyeong Jun Lee, Tae Yang Choi, Seo Hyoung Chang, Hu Young Jeong, Younghak Kim, Suyoun Lee, Young Jun Chang Chromium telluride (Cr1-δTe) has been known as a p-type ferromagnetic metal with varied Curie temperatures (Tc = 170 K – 340 K). Recently report of topological Hall effect (THE) suggested the skyrmion phase formation (Nano Research, 11, 3116 (2017)). However, the origin of THE as well as the various Tc among the Cr1-δTe phases was not clearly understood yet. Here, we investigate two different types of Cr1-δTe thin films with different Tc via different growth conditions to understand the origin of the various Tc. We also discuss the THE-like signal in our Hall measurements, with complementary microscopic and spectroscopic evidences, to address the origin of observed THE-like signal in this peculiar magnetic thin film system. |
Friday, March 6, 2020 8:24AM - 8:36AM |
W41.00003: Large topological Hall effect in a non-coplanar ferromagnet Cr0.9TeB0.1 Yangkun He, Gerhard Fecher, Johannes Kroder, Chenguang Fu, Yu Pan, Walter Schnelle, Horst Borrmann, Claudia Felser The Berry phase understanding of electronic properties has attracted special interest in condensed matter physics, leading to phenomena such as anomalous Hall effect (AHE) and topological Hall effect (THE). A non-zero Berry phase, induced by band structure in momentum space or non-coplanar spin structure is the origin of both effects. Here, we report a sign change in AHE and the origin of THE in Cr0.9TeB0.1 single crystal, due to a non-coplanar canted magnetic structure and the momentum space Berry curvature. At high temperatures, the moments are aligning ferromagnetically along the c axis, while non-coplanar canted magnetic structure is found below 140 K. The cone angle subtended by the spins depends on the temperature. This spin-reorientation leads to the change of Berry curvature, which influences both AHE and THE in the presence of an applied magnetic field and current. Our study provides a deep understanding of the relation between spin structure and Hall signal. |
Friday, March 6, 2020 8:36AM - 8:48AM |
W41.00004: Topological Hall effect in Shastry-Sutherland lattice Munir Shahzad, Nyayabanta Swain, Pinaki Sengupta We study the classical Heisenberg model on the geometrically frustrated Shastry-Sutherland lattice with additional Dzyaloshinskii-Moriya (DM) interaction. We show that several noncollinear and noncoplanar magnetic states such as flux, all-out, 3in-1out, canted-flux are stabilized over wide range of parametric space in the presence of DM interaction. We discuss the role of different DM vectors in the stabilization of these complex configurations of localized moments. These ordered states not only drive exotic magnetic properties but also anomalous magneto-transport. The spin of itinerant electron moving on the background of these localized spins acquires a Berry phase which manifests itself by contributing an extra term in Hall conductivity known as geometrical or topological Hall effect. We demonstrate this effect by calculating the energy bands and transverse conductivity for conduction electrons hopping on these localized moments. It is shown that transverse conductivity is non-zero for several of these noncoplanar ordered states even in the absence of magnetic field coupling to the conduction electrons. |
Friday, March 6, 2020 8:48AM - 9:00AM |
W41.00005: Recent Developments in Spin Superfluid Transport Daniel Hill, Yaroslav Tserkovnyak Spin Superfluidity, also called Dissipative Exchange Flow to emphasize its distinguishing features from traditional superfluids, is coherent spin transport mediated by topological winding in the texture of a magnetic order parameter. Experimental signatures for Spin Superfluids have been observed in recent years, most notably in antiferromagnets and amorphous magnets; however, in some respects experimental progress has been surprisingly elusive, especially for ferromagnets. Experimental observation of ferromagnetic spin superfluids may require overcoming various problems, such as pinning due to the effective anisotropy induced by strong demagnetizing fields of thin films, as well as spin current screening due to soliton formation at the boundary. We discuss how some of these problems are actually features which lead to a rich and potentially useful non-equilibrium phase diagram. In addition, we show how spin superfluid signals could propagate through a 3D amorphous magnet, despite the spin superfluid being unstable due to a lack of barriers to phase slips. |
Friday, March 6, 2020 9:00AM - 9:12AM |
W41.00006: Magnetic and electrical transport properties of MnBi2Te4 Dongliang Gong, Rongying Jin MnBi2Te4 is considered as an intrinsic antiferromagnetic topological insulator. We have successfully synthesized MnBi2Te4 single crystals. The magnetic susceptibility measurements indicate that the Neel temperature TN = 25 K with the easy axis along the c direction. Below TN, the system undergoes a spin flop transition at Hsf when the magnetic field (H) is applied along the c axis with H > Hsf. The critical field Hsf increases with decreasing temperature, reaching 3.5 Tesla at 2 K. Correspondingly, both the magnetoresistance and Hall resistivity show anomaly at Hsf. Detailed data analysis and implication will be presented. |
Friday, March 6, 2020 9:12AM - 9:24AM |
W41.00007: Magnetization and transport measurement of Cr11Ge19 single crystal Yu Li, David P Young, John Ditusa We have successfully synthesized single crystal of Cr11Ge19 which has been proved as a candidate hosting magnetic bi-skyrmion. We carried out a series of measurements on its magnetic susceptibility and transport properties. Our results demonstrate the complex magnetism in Cr11Ge19 and confirmed the existence of nontrivial spin texture in this material. |
Friday, March 6, 2020 9:24AM - 9:36AM |
W41.00008: Giant anomalous Hall effect related to scalar spin chirality induced by spin-cluster scattering Hiroaki Ishizuka, Naoto Nagaosa Anomalous Hall effect (AHE) related to spin chirality, so-called topological Hall effect (THE), has been an important topic that involves a wide range of fields such as transport phenomena, topological materials, and magnetism. Since its proposal, most of the studies on THE focuses on the intrinsic mechanism. On the other hand, a recent theory proposed that an extrinsic mechanism for the chirality-related Hall effect also exists, in which the skew scattering of electrons by three-spin clusters produces a Hall effect proportional to the spin chirality. This mechanism is qualitatively different from the other AHEs because the spin-orbit interaction is unnecessary, potentially showing a distinct behavior from the conventional notion of AHE. |
Friday, March 6, 2020 9:36AM - 9:48AM |
W41.00009: Giant anomalous Hall effect from spin-chirality scattering in a chiral magnet Yukako Fujishiro, Naoya Kanazawa, Ryosuke Kurihara, Atsushi Tsukazaki, Masakazu Ichikawa, Masashi Kawasaki, Masashi Tokunaga, Yoshinori Tokura Topological spin textures give rise to various emergent phenomena, which originate from the interplay between scalar-spin chirality and conduction electrons. In that sense, a spin hedgehog lattice in MnGe provides one distinct example, where the dense emergent magnetic field (~ 40 T) and its fluctuations lead to novel electrodynamics. |
Friday, March 6, 2020 9:48AM - 10:00AM |
W41.00010: Thermal Response Functions of Insulating Magnets Near and Beyond Critical Temperature Caitlin Carnahan, Yinhan Zhang, Di Xiao Thermal response coefficients of magnetic materials are of significant interest in the field of spintronics; understanding spin dynamics in response to a thermal gradient paves the way for energy-efficient spin manipulation via thermal fluctuations. We investigate thermal response in magnetic systems, particularly near and above the critical temperature, by simulating the dynamics of these systems and calculating the spin and energy currents that appear. Applying linear response theory, we predict the thermal conductivities of both spin and energy, which provide insight into how thermally-induced fluctuations impact transport in magnetic systems and deepen the understanding of the general effect of fluctuations on non-trivial magnetic topology. |
Friday, March 6, 2020 10:00AM - 10:12AM |
W41.00011: Anomalous Hall Effect sensor based on CoFeB with ultrahigh magnetic field detectability Yiou Zhang, Kang Wang, Gang Xiao The anomalous Hall Effect (AHE) in ferromagnetic metals and alloys have been widely studied as a potential candidate for magnetic sensing applications, due to the relative easiness of fabrication, broad frequency response and lower intrinsic noise. Nevertheless, AHE sensor suffers from relatively low sensitivity in comparison with semiconductor Hall sensor. In this work, we have demonstrated that sensitivity of AHE sensor based on Ta/CoFeB/MgO/Ta multi-layer structure can be greatly enhanced, through engineering of magnetic anisotropy. By tuning thickness of CoFeB layer as well as the annealing temperature, ultra-high sensitivity (1000 V/A/T, comparable to that of semiconductor Hall sensor) and zero hysteresis can be achieved. We have also performed noise measurement over a broad frequency range. The low-frequency 1/f noise is found to strongly depend on input current and bias magnetic field, while the high-frequency white noise shows much weaker dependence. The best magnetic field detectability of our AHE sensor reaches 70 nT/rtHz at 1 Hz and 10 nT/rtHz at 1 kHz. Our work shows that AHE sensors are suitable for ultra-small magnetic field sensing applications. |
Friday, March 6, 2020 10:12AM - 10:24AM |
W41.00012: Atomic antiferromagnetic domain wall propagation beyond the relativistic limit Huanhuan Yang, Huaiyang Yuan, Ming Yan, H. W. Zhang, Peng Yan We theoretically investigate the dynamics of atomic domain walls (DWs) in antiferromagnets driven by a spin-orbit field. For a DW with a width of a few lattice constants, we identify a Peierls-like pinning effect, with the depinning field exponentially decaying with the DW width, so that a spin-orbit field moderately larger than the threshold can drive the propagation of an atomic DW in a stepwise manner. For a broad DW, the Peierls pinning is negligibly small. However, the external spin-orbit field can induce a fast DW propagation, accompanied by a significant shrinking of its width down to atomic scales. Before stepping into the pinning region, noticeable spin waves are emitted at the tail of the DW. The spin-wave emission event not only broadens the effective width of the DW but also pushes the DW velocity over the magnonic barrier, which is generally believed to be the relativistic limit of the DW speed. While the existing dynamic theory based on the continuum approximation fails in the atomic scale, we develop an energy conversion theory to interpret the DW dynamics beyond the relativistic limit. |
Friday, March 6, 2020 10:24AM - 10:36AM |
W41.00013: Transport signature of the BKT transition in 2D easy-plane magnets Suk Bum Chung, Se Kwon Kim The theory of the Berezinskii-Kosterlitz-Thouless (BKT) phase transition was formulated to describe the 2D phase transition of easy-plane magnets as well as 2D superconductors and superfluids. The BKT transition being topological in nature, i.e. not characterized by a local order parameter, its detection has been challenging. The BKT transitions in the latter cases have been observed in experiments, much of which involves transport signatures, such as the current-voltage relation being non-linear below the BKT temperature and linear above the BTK temperature. By contrast, the experimental study of the solid-state 2D magnetic material emerged only in the last few years. The accompanied recent development of spin-transport measurements offers a tantalizing opportunity to discover novel transport phenomena of spin, which should be expected as the spin, unlike the particle number, is not conserved. In this Letter, we show here that this non-conservation of spin in the 2D easy-plane magnets leads to a distinct spin transport signature at the BKT transition, the crossover between the infinitely long-range spin transport and the exponentially decaying spin transport. We also present how this can be detected in the van der Waals easy-plane magnetic materials such as the monolayer NiPS3. |
Friday, March 6, 2020 10:36AM - 10:48AM |
W41.00014: Frequency Dependence of Magnetic and Magnetoelastic Properties of Magnetostrictive Materials for Multiferroic Antennae Peter Finkel, Nicholas Jones, Margo Staruch Magnetoelectric (ME) resonators are of significant interest for pure mechanically driven antennae targeting the ULF/VLF radio frequency range. Direct coupling of magnetostrictive and piezoelectric phases in the ME composites enables time variable magnetic field generation with exceptionally low operational power requirements. A dynamic stress loading of the magnetoelastic/magnetostrictive material by piezoelectric element results in a fluctuating magnetic field. In this work we fully characterize magnetostrictive materials Fe81.6Ga18.4 and Terfenol-D at high frequencies up to several kHz and studied the effect of eddy current losses that potentially curtail the magnetic response of the material. We evaluated the dynamic response of Galfenol rod up to 1000 Hz comparing both its sensing response (changing dynamic stresses) to its actuation response (changing dynamic magnetic fields) in both solid and laminated rods. |
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