Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session R22: Topological Hall Effect and Transport Phenomena in Chiral MagnetsFocus
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Sponsoring Units: GMAG DMP Chair: Shulei Zhang, Argonne Natl Lab Room: LACC 402A |
Thursday, March 8, 2018 8:00AM - 8:12AM |
R22.00001: Theory of Transport in Skyrmion Systems: Topological Hall Effect Tim McCormick, James Rowland, Nandini Trivedi, Mohit Randeria Skyrmion materials have attracted substantial recent interest, particularly for the effect of magnetic textures on the motion of itinerant electrons. Measurements of the Hall resistivity have usually been analyzed using a sum of the regular Hall effect and the anomalous Hall effect, and interpreting the remaining signal as a topological Hall effect. The topological Hall resistivity is then described using a simple model where the real-space Berry curvature of itinerant electrons is described as a uniform magnetic field with magnitude proportional to skyrmion density. In this talk, we will present a theory of electronic transport in systems with spin-orbit coupled itinerant electrons coupled to chiral magnetic textures, where we analyze Berry curvature effects in real- and momentum-space in both the semi-classical and quantum regimes. |
Thursday, March 8, 2018 8:12AM - 8:24AM |
R22.00002: Topological Hall effect in weak coupling regime Kazuki Nakazawa, Manuel Bibes, Hiroshi Kohno Topological Hall effect (THE) arises from the exchange coupling M of conduction electrons to the magnetization texture having a scalar spin chirality. It is understood in terms of the effective magnetic field, Beff, due to Berry phase in the strong coupling regime. In this case, electrons adjust their spin to the local magnetization, and Beff is determined by the “local” magnetic structure. However, in the weak coupling regime, electrons fail in such adjustment and Beff will be determined by a “nonlocal” spin chirality. |
Thursday, March 8, 2018 8:24AM - 8:36AM |
R22.00003: Unexpectedly Large Skyrmion Topological Hall Effect near Room Temperature in Mesoscopic FeGe Maxime Leroux, Matthew Stolt, Song Jin, Douglas Pete, Charles Reichhardt, Boris Maiorov Magnetic skyrmions are nanometer sized topological spin structures proposed as building blocks of future memory devices with high density and low power consumption. Skyrmions give rise to a Topological Hall Effect (THE) that could be used for detection in memory bits. Even though the stabilization temperature of skyrmions in FeGe is near room temperature, its THE was assumed to be below detection limits because of the larger skyrmion size. I will present the first observation of skyrmion THE near room temperature (276 K, 3 °C) in a mesoscopic lamella extracted from a FeGe crystal with a Focused Ion Beam. This THE has an unexpectedly large magnitude (+5 nΩ.cm), and it unambiguously coincides with the skyrmion lattice revealed by neutron scattering. Hall Effect measurements also point to a reentrant magnetic phase adjacent to the skyrmion phase. We explain the large THE as result of a large normal Hall constant, revealing a new route to enhance THE, a requirement for electrical detection of skyrmions. |
Thursday, March 8, 2018 8:36AM - 8:48AM |
R22.00004: Topological Hall Effect in Ultra-thin SrRuO3 film Byungmin Sohn, Bongju Kim, Youngjae Choi, Tae Won Noh, Changyoung Kim With extensive interests on novel oxide-based devices such as electronics and spintronics, the 4d transition metal compounds have been considered as promising candidates. Especially, SrRuO3 is well-known for an itinerant ferromagnetic metal with a high Curie temperature , leading to anomalous Hall effect (AHE) below . Owing to the intense study on Hall effect in SrRuO3 thin films, the mechanism of Hall effect has been well-established. Here, we observed extraordinary Hall effect in high-quality SrRuO3 ultra-thin films grown by pulsed laser deposition (PLD), which cannot be explained in terms of simple AHE. We claim that this extraordinary Hall effect can be understood as topological Hall effect, which occurs due to emergent electromagnetic field (EEMF) derived from Skyrmion spin texture. Moreover, the Skyrmion phase is extremely stable with sustaining large external magnetic field range, about 1 Tesla. We suggest that the large spin orbit coupling of Ru ions and the inversion symmetry breaking produce Dzyaloshinskii-Moriya (DM) interaction and consequently the Skyrmion phase is formed in ultra-thin SrRuO3 film. |
Thursday, March 8, 2018 8:48AM - 9:00AM |
R22.00005: Image Simulation of Magnetic Skyrmions on Oxygen Deficient EuO1-x with Spin-polarized Scanning Tunneling Microscopy Aaron Wang, Te-Yu Chien Magnetic skyrmions are topologically protected nanometer-sized nontrivial spin textures. Here we present the simulation images of magnetic skyrmions with spin-polarized scanning tunneling microscopy (SP-STM) on EuO1-x. With the observed topological hall effect (THE), magnetic skyrmion is suspected to exist in EuO1-x. Other evidences point to the oxygen vacancies are closely related to this THE related magnetic topological states. Among the various techniques of probing skyrmions, SP-STM is one with direct imaging and high spatial resolution, capable of visualizing non-ordered skymions, in contrast to the skyrmion lattice probed by neutron scattering. SP-STM has ferromagnetic or antiferromagnetic materials on the tip apex. The tunneling current is determined by the angle between the spin orientations of the tip apex and the sample surface. Through simulations, it is concluded that the in-plane (with unknown spin orientation) and out-of-plane spin polarized tip scanning over various types of skyrmion textures could identify the existence of the skyrmions in EuO1-x. Furthermore, with the known in-plane spin orientation, specific type of skyrmion can be determined. |
Thursday, March 8, 2018 9:00AM - 9:12AM |
R22.00006: Numerical study of the electronic state and transport properties in a chiral soliton lattice Shun Okumura, Yasuyuki Kato, Yukitoshi Motome Chiral magnets often show interesting properties associated with their peculiar spin structures. A typical example is a chiral soliton lattice (CSL), which was found in a monoaxial chiral magnets CrNb3S6 [1] and Yb(Ni1-xCux)3Al9 [2]. These compounds show a helical spin spiral at zero field, and turn into the CSL in a magnetic field perpendicular to the helical axis. To clarify the electronic and transport properties in the CSL, it is crucial to take into account itinerant electrons; nevertheless, most of the previous studies were focused on localized spin models. Here, we investigate a minimal itinerant electron model, a one-dimensional Kondo lattice model with the Dzyaloshinskii-Moriya interaction, by Monte Carlo simulation and variational calculations. We show that the system exhibits nonlinear negative magnetoresistance in the CSL, which is closely related to the soliton density [3]. We also find that the periodicity of CSL can be locked at commensurate values dictated by the Fermi wave number, which suggests the possibility of spontaneous formation of the CSL even at zero field. |
Thursday, March 8, 2018 9:12AM - 9:24AM |
R22.00007: Electrical magnetochiral effect induced by chiral spin fluctuations in MnSi Tomoyuki Yokouchi, Naoya Kanazawa, Akiko Kikkawa, Daisuke Morikawa, Kiyou Shibata, Taka-hisa Arima, Yasujiro Taguchi, Fumitaka Kagawa, Yoshinori Tokura Chirality of matter can give rise to unique responses in optics, electricity and magnetism. One such example is electrical magnetochiral effect (eMChE), which is directional nonlinear magnetotransport in proportion to an inner-product of B and j [1,2]. Electrical magnetochiral effect in magnetic materials has not been reported so far. |
Thursday, March 8, 2018 9:24AM - 9:36AM |
R22.00008: Numerical investigations of itinerant electrons coupled to skyrmion lattice Yuanda Liao, ZiYang Meng, Xiaopeng Li We investigate the properties of fermions coupled to skyrmion lattice in frustrated spin system with Self-learning Monte-Carlo (SLMC) and Kernel Polynomial Method (KPM). SLMC captures the low-energy physics of the coupled system and provides global update of spin configurations, and KPM is an efficient algorithm to calculate spectral quantities and various correlation functions of the itinerant electrons. By means of such unbiased numerical tools, the novel spectral and transport properties of itinerant electrons in the presence of effective gauge field generated by the skyrmion lattice spin background, are revealed with high accuracy. |
Thursday, March 8, 2018 9:36AM - 9:48AM |
R22.00009: Large Magneto-thermopower in MnGe with topological spin texture Yukako Fujishiro, Naoya Kanazawa, Takahiro Shimojima, Asuka Nakamura, Kyoko Ishizaka, Takashi Koretsune, Ryotaro Arita, Atsushi Miyake, Hiroyuki Mitamura, Kazuto Akiba, Masashi Tokunaga, Shojiro Kimura, Satoshi Awaji, Shiogai Junichi, Atsushi Tsukazaki, Akiko Kikkawa, Yasujiro Taguchi, Yoshinori Tokura A topological spin texture—a three-dimensional array of hedgehogs and anti-hedgehogs—shows up in a chiral magnet MnGe. Those hedgehog-type spin textures serve as “emergent” magnetic monopoles whose fluctuations critically affect charge transport phenomena. |
Thursday, March 8, 2018 9:48AM - 10:00AM |
R22.00010: Topological Hall effect in spin-orbit coupling TI thin film Jianxiao Zhang, Chao-Xing Liu In this report, we examined the coexistence of SOC-induced intrinsic anomalous Hall effect and skyrmion-induced topological Hall effect in a TI thin film. Numerical Green's function transport calculation suggests the possibility of a reversed sign of transverse voltage due to the competence of these mechanisms. |
Thursday, March 8, 2018 10:00AM - 10:12AM |
R22.00011: Skyrmion electrical detection with the use of three-dimensional topological insulator / magnetic bilayers Dimitrios Andrikopoulos, Bart Soree In this work, we numerically investigate the effect of the magnetic skyrmion texture on the transport properties of the topological insulator surface state. It is shown that both Bloch and Nèel skyrmion textures interacting via proximity-induced exchange coupling with the surface state electrons, induce additional scattering on top of a homogeneous background ferromagnetic texture which can modify the conductance of the system. The change in conductance depends on the skyrmion size, the dimensions of the magnetic system and the exchange interaction strength. For the Nèel skyrmion, the result of the interaction strongly depends on the skyrmion number Nsk and the skyrmion helicity h. For both skyrmion types, significant change of the resistance can be achieved, which can be in the order of kΩ. |
Thursday, March 8, 2018 10:12AM - 10:24AM |
R22.00012: Anomalous transverse response in Mn3X (X=Sn, Ge) Zengwei Zhu, Xiaokang Li, Liangcai Xu, Linchao Ding, Jinhua Wang, Mingsong Shen, Xiufang Lu, Kamran Behnia In ferromagnets, there is an Anomalous Hall Effect (AHE) due to spontaneous magnetization. Recently, in a family of nonlinear antiferromagnets, Mn3X (X=Sn, Ge), an unexpectedly large AHE has been detected and attributed to a nonvanishing Berry [1-3]. We present, a study of electric, thermoelectric and thermal transport in Mn3X (X=Sn, Ge). The three anomalous transverse conductivities (Hall, Nernst, and Righi-Leduc) were quantified. The thermal and electrical Hall conductivities respect the Wiedemann-Franz law over the whole temperature range of study in Mn3Sn [4]. We also carried out a study of angle-dependent AHE shedding additional light to the origin of anomalous transverse flow and their link to the locus of the Weyl nodes. |
Thursday, March 8, 2018 10:24AM - 10:36AM |
R22.00013: Magnon Hall effect in kagome antiferromagnets with Dzyaloshinskii-Moriya interactions Pontus Laurell, Gregory Fiete We theoretically study magnetic properties of kagome antiferromagnets with both in- and out-of-plane Dzyaloshinskii-Moriya interactions, such as the iron jarosites and the recently introduced spin-1/2 compound Nd3Sb3Mg2O14. At low temperatures these systems order in a 120 degree spin configuration canted out of plane, resulting in a noncoplanar order with finite scalar spin chirality. We derive an expression for the canting angle in the presence of applied magnetic fields. We also study the spin wave properties as a function of canting, generically finding topological magnon bands at nonzero canting. Finally we calculate the resulting thermal Hall conductivity, and show how it can be controlled using magnetic fields. |
Thursday, March 8, 2018 10:36AM - 10:48AM |
R22.00014: Magnon-mediated analog to the Edelstein effect in an antiferromagnet Bo Li, Alexander Mook, Alexey Kovalev In metallic and semiconducting materials, the Edelstein effect produces a non-zero average non-equilibrium spatially homogeneous spin polarization by applied external electric field due to the imbalance of spin relaxation time of system with spin degeneracy lift by spin-orbital coupling (SOC). For magnons, the Dzyaloshiniskii-Moriya interaction (DMI) can play similar role to the SOC in a semiconductor and it can result in a non-equilibrium spatially homogeneous spin polarization in collinear and noncollinear insulating antiferromagnets under a temperature gradient. Using the linear response theory, we theoretically predict that by applying a temperature gradient to insulating antiferromagnet with spin non-conserving Hamiltonian, one can produce homogeneous spin accumulation mediated by magnons. We applied our theory to honeycomb, kagome, and pyrochlore collinear and noncollinear antiferromagnets. This prediction can be applied as a new way to generate spin currents in antiferromagnetic spintronic devices. |
Thursday, March 8, 2018 10:48AM - 11:00AM |
R22.00015: Photonic orbital angular momentum transfer and magnetic skyrmion rotation Wenrui Yang, Huanhuan Yang, Yunshan Cao, Peng Yan Magnetic skyrmions are chiral quasiparticles that show promise for future spintronic applications such as |
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