Bulletin of the American Physical Society
APS March Meeting 2016
Volume 61, Number 2
Monday–Friday, March 14–18, 2016; Baltimore, Maryland
Session B6: Dzyaloshinskii-Moriya InteractionFocus Industry
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Sponsoring Units: GMAG DMP FIAP Chair: Emilie Jue, NIST Room: 302 |
Monday, March 14, 2016 11:15AM - 11:27AM |
B6.00001: Proportionality of the interfacial Dzyaloshinskii-Moriya interaction and the Heisenberg exchange Hans Nembach, Justin Shaw, Mathias Weiler, Emilie Jué, Tom Silva The Dzyaloshinkii-Moriya interaction (DMI) gives rise to chiral magnetic ordering and a shift of spin-wave frequencies, depending on their propagation direction. We employed Brillouin-Light-Scattering spectroscopy to measure this nonreciprocal frequency shift, which allowed us to directly determine the magnitude of the DMI in a series of Ni$_{\mathrm{80}}$Fe$_{\mathrm{20}}$(t)/Pt thin film bilayers where the thickness t ranged from 1 to 13 nm. It has also been predicted by theory that the DMI is proportional to the Heisenberg exchange for bulk magnetic oxides and metallic spin-glasses. We tested this prediction for our metallic system by independently determining the Heisenberg exchange via fitting the Bloch T$^{\mathrm{3/2}}$-law to the temperature dependence of the magnetization obtained from SQUID magnetometry. We find that the Ni$_{\mathrm{80}}$Fe$_{\mathrm{20}}$ thickness dependence of the DMI and the Heisenberg exchange are identical, which is consistent with the notion that both effects share the same underlying physics. This result will lead us to a deeper understanding of the DMI and related spin-orbitronic effects.-/ [Preview Abstract] |
Monday, March 14, 2016 11:27AM - 11:39AM |
B6.00002: Nonreciprocal magnon propagation in a noncentrosymmetric ferromagnet LiFe$_{5}$O$_{8}$ Yusuke Iguchi, Soichiro Uemura, Kazunori Ueno, Yoshinori Onose In noncentrosymmetric materials, the relativistic effect extensively modifies the energy band of magnons as well as that of electrons. With use of microfabricated microwave antennae, we have demonstrated that the propagation of magnons with large momentum is nonreciprocal in a noncentrosymmetric ferromagnet LiFe$_{5}$O$_{8}$. The nonreciprocity is clearly explained by the effect of asymmetric magnon band originating from the relativistic Dzyaloshinskii-Moriya interaction. This result may pave a new path to designing magnonic device based on the relativistic band engineering. [Preview Abstract] |
Monday, March 14, 2016 11:39AM - 11:51AM |
B6.00003: A Dzyaloshinskii-Moriya Anisotropy in nanomagnets with in-plane magnetization M. Cubukcu, J. Sampaio, A. V. Khvalkovskiy, D. Apalkov, V. Cros, N. Reyren The Dzyaloshinskii-Moriya interaction (DMI) is known to be a direct manifestation of spin-orbit coupling in systems with broken inversion symmetry. We present a new anisotropy for in-plane-magnetized nanomagnets which is due to the interfacial DMI. This new anisotropy depends on the shape of the magnet, and is perpendicular to the demagnetization shape anisotropy [1]. The DMI anisotropy term that we introduce here results from the DMI energy reduction due to an out-of-plane tilt of the spins at the edges that are oriented perpendicular to the magnetization. For large enough DMI, the reduction of the DMI and anisotropy energies takes over the demagnetization energy cost when magnetization lies along the minor axis of a structure. Our experimental, numerical and analytical results demonstrate this prediction in magnets of elongated shape for small enough volume (and thus quasi-uniform magnetization). Our results also provide the first experimental evidence of the interfacial DMI-induced tilt of the spins at the borders. [1] M. Cubukcu \textit{et al.,} \textit{arXiv:}1508.02961 (2015). [Preview Abstract] |
Monday, March 14, 2016 11:51AM - 12:03PM |
B6.00004: ABSTRACT WITHDRAWN |
Monday, March 14, 2016 12:03PM - 12:15PM |
B6.00005: Torque, spin and energy Hall currents in magnets with Dzyaloshinskii-Moriya interactions Vladimir Zyuzin, Alexey Kovalev Within a linear response theory, we study nonequilibrium magnonic torques as well as spin and energy Hall currents generated by thermal gradients in ferromagnetic and anti-ferromagnetic systems. We predict a contribution related to Berry curvature which arises in multiband systems with topologically non-trivial magnon bands. We identify symmetries that need to be broken in order to have non-vanishing nonequilibrium magnonic torques. As an example, we study kagome lattice of spins with various symmetries of Dzyaloshinskii-Moriya interactions. [Preview Abstract] |
Monday, March 14, 2016 12:15PM - 12:27PM |
B6.00006: Magnon Chirality Hall Effect in Antiferromagnet Ran Cheng, Nikhil Sivadas, Satoshi Okamoto, Di Xiao In a collinear antiferromagnet with easy-axis anisotropy, symmetry dictates that the spin wave modes must be doubly degenerate with opposite chirality. We show that in the presence of the Dzyaloshinskii-Moriya interaction, there exist a magnon chirality Hall effect, where magnons with opposite chirality flow to opposite transverse edges when an in-plane temperature gradient is applied. Possible material candidates to realize this effect is also discussed. [Preview Abstract] |
Monday, March 14, 2016 12:27PM - 1:03PM |
B6.00007: Soliton-like magnetic domain wall motion induced by the interfacial Dzyaloshinskii-Moriya interaction Invited Speaker: Teruo Ono Topological defects such as magnetic solitons, vortices, Bloch lines, and skyrmions start to play an important role in modern magnetism due to their extraordinary stability which can be hailed as future memory devices. Recently, novel type of antisymmetric exchange interaction, namely the Dzyaloshinskii-Moriya interaction (DMI), has been uncovered and found to influence on the formation of topological defects. Exploring how the DMI affects the dynamics of topological defects is therefore an important task. Here we investigate the dynamics of the magnetic domain wall (DW) under a DMI by developing a time-of-flight measurement scheme which allows us to measure the DW velocity for magnetic fields up to 0.3T. For a weak DMI, the trend of DW velocity follows the Walker's model which predicts that the velocity of DW increases with field up to a threshold (Walker field) and decreases abruptly. On the other hand, for a strong DMI, velocity breakdown is completely suppressed and the DW keeps its maximum velocity even far above the Walker field. Such a distinct trend of the DW velocity, which has never been predicted, can be explained in terms of magnetic soliton, of which topology can be protected by the DMI. Importantly, such a soliton-like DW motion is only observed in two dimensional systems, implying that the vertical Bloch lines (VBLs) creating inside of the magnetic domain-wall play a crucial role. This work was partly supported by JSPS KAKENHI Grant Numbers 15H05702, 26870300, 26870304, 26103002, 25·4251, Collaborative Research Program of the Institute for Chemical Research, Kyoto University, and R {\&} D Project for ICT Key Technology of MEXT from the Japan Society for the Promotion of Science (JSPS). [Preview Abstract] |
Monday, March 14, 2016 1:03PM - 1:15PM |
B6.00008: Magnetoelectric effects in the spin 1/2 XX chain with three spin interactions and Dzyaloshinskii-Moriya interaction P Durganandini We consider the spin 1/2 XX chain with three spin interactions of the XZX+YXY and XZY-YZX types in an external magnetic field and with Dzyaloshinskii-Moriya (D-M) interaction. Interpreting the D-M interaction as a local electric polarization, we study the magnetoelectric effects in the system by using the exact solution of the problem. We obtain the ground state phase diagram by calculating the electric polarization, magnetization and isentropes. There are various regimes of magnetic and electric polarization depending on the relative strengths of the three spin interaction as well as that of the external fields. For a certain range of three spin interaction strengths, the system shows the existence of finite magnetization and electric polarization even in the absence of any external fields. The external electric and magnetic fields modify the ground state phases and can be used to tune the various regimes. We also calculate the entropy and analyze the electrocaloric and magnetocaloric effects. We show that the electrocaloric and magnetocaloric effects can be used to obtain information about the magnetoelectric effects in the system. [Preview Abstract] |
Monday, March 14, 2016 1:15PM - 1:27PM |
B6.00009: Large anomalous Hall effect in a non-collinear antiferromagnet Mn$_{3}$Sn at room temperature Tomoya Higo, Naoki Kiyohara, Satoru Nakatsuji Recent development in theoretical and experimental studies have provided a framework for understanding the anomalous Hall effect using Berry-phase concepts, and this perspective has led to predictions that, under certain conditions, a large anomalous Hall effect may appear in spin liquids and antiferromagnets [1, 2]. In this talk, we will present experimental results showing that the antiferromagnet Mn$_{3}$Sn, which has a non-collinear 120-degree spin order, exhibits a large anomalous Hall effect [3]. The magnitude of the Hall conductivity is $\sim$ 20 $\Omega^{-1}$ cm$^{-1}$ at room temperature and $>$ 100 $\Omega^{-1}$ cm$^{-1}$ at low temperatures. We found that a main component of the Hall signal, which is nearly independent of a magnetic field and magnetization, can change the sign with the reversal of a small applied field, corresponding to the rotation of the staggered moments of the non-collinear antiferromagnetic spin order which carries a very small net moment of a few of m$\mu_{\rm B}$. [1] N. Nagaosa $et \ al$., Rev. Mod. Phys. $\bf{82}$, 1539 (2010). [2] Y. Machida $et \ al$., Nature $\bf{463}$, 210 (2010). [3] S. Nakatsuji, N. Kiyohara and T. Higo, Nature, doi:10.1038/nature15723, (2015). [Preview Abstract] |
Monday, March 14, 2016 1:27PM - 1:39PM |
B6.00010: Nanoscale and proximity effects on low-dimensional helical magnetic structures Leonid Sandratskii, J. Fisher, S. Park, S. Ouazi, D. Sander, J. Kirschner We combine symmetry arguments, first-principles calculations and spin-resolved STS measurements to study a 2D helical magnet of some nm extension in proximity to ferromagnetic Co and vacuum regions. Considering the prototypical helical 2D system, an Fe bilayer with intrinsic helical spin structure (1), we report a non-uniform distortion of the spin helix which depends on the lateral extension of the bilayer and on the proximity to either Co or vacuum. The proximity effect manifests itself in different modifications of the magnetic and electronic structures of Fe in vicinity of the interfaces with Co and vacuum. These nanosize and proximity effects have not been discussed before. We demonstrate that, in contrast to an ideal helix of infinite length, the lack of symmetry of the nm-long distorted Fe spin helix, induces an energy dependence of the direction of the electronic magnetization which is revealed in the measured energy dependence of the spin-asymmetry of the differential tunneling conductance. (1) Phark, S. H.; Fischer, J. A.; Corbetta, M.; Sander, D.; Nakamura, K. & Kirschner, J. Reduced-dimensionality-induced helimagnetism in iron nanoislands Nat Commun 5 (2014) 5183. [Preview Abstract] |
Monday, March 14, 2016 1:39PM - 1:51PM |
B6.00011: Emergence of magnetic order in ultra-thin pyrochlore iridate films Suraj Cheema, Claudy Serrao, Julia Mundy, Shreyas Patankar, Robert Birgeneau, Joseph Orenstein, Sayeef Salahuddin, Ramamoorthy Ramesh We report on thickness-dependent magnetotransport in (111) - oriented Pb$_{2}$Ir$_{2}$O$_{7-x}$ (Pb227) epitaxial thin films. For thicknesses greater than 4 nm, the magnetoresistance (MR) of metallic Pb227 is positive, linear and non-saturated up to 14 T. Meanwhile at 4 nm, the conduction turns nonmetallic and the MR becomes negative and asymmetric upon field-cooling; such traits are reminiscent of all-in-all-out (AIAO) magnetic order in the insulating pyrochlore iridates. Hysteretic low-field MR dips and trained-untrained resistivity bifurcations suggest the presence of magnetic conducting domain walls within the chiral AIAO spin structure. Beyond just AIAO order, angular-dependent MR indicates a magnetic phase space hosting 2-in-2-out (2I2O) spin ice order. Such anomalous magnetotransport calls for re-evaluation of the pyrochlore iridate phase diagram, as epitaxially strained Pb227 exhibits traits reminiscent of both the insulating magnetic and metallic spin-liquid members. Furthermore, these results open avenues for realizing topological phase predictions in (111) - oriented pyrochlore slabs of kagome-triangular iridate heterostructures. [Preview Abstract] |
Monday, March 14, 2016 1:51PM - 2:03PM |
B6.00012: Modulated magnetic ground state and complex phase diagram in the chiral helimagnet Cr$_{\mathrm{1/3}}$NbS$_{\mathrm{2}}$ EM Clements, R Das, L Li, P Lampen-Kelley, MH Phan, Veerle Keppens, D Mandrus, H Srikanth The chiral helimagnetic ground state of noncentrosymmetric Cr$_{\mathrm{1/3}}$NbS$_{\mathrm{2}}$ originates from competition between coexisting symmetric ferromagnetic (FM) exchange and the antisymmetric Dzyaloshinskii-Moriya (DM) interaction. Previously, it has been shown via Lorentz microscopy that a field induced chiral soliton lattice (SL) exists followed by an incommensurate-commensurate metamagnetic transition to a FM state. The high crystalline anisotropy as well as magnetic and temperature control of the c-axis oriented spin spiral has generated interest for spintronic applications. Currently, only a preliminary phase diagram has been proposed and details of the phase evolution, specifically from the paramagnetic (PM) to the helicoid HM and SL states, have not yet been determined. In this study, we exploit the magnetocaloric effect (MCE) to construct a phase diagram by determining the magnetic entropy change ($\Delta $S$_{\mathrm{M}})$ under the influence of applied field and temperature variations. Well below the Curie temperature (T$_{\mathrm{c}}\sim $131K) we see the onset of SL formation at $\sim $1kOe and a FM transition $\sim $1.2kOe. A negative $\Delta $S$_{\mathrm{M}}$ value indicates that the system also shows weak FM behavior in a narrow region just below T$_{\mathrm{c}}$, where thermal fluctuations destabilize the weaker DM coupling, before transitioning into the HM phase at lower temperatures. [Preview Abstract] |
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