Bulletin of the American Physical Society
APS March Meeting 2017
Volume 62, Number 4
Monday–Friday, March 13–17, 2017; New Orleans, Louisiana
Session H47: Spin Seebeck and Spin Nernst EffectsFocus
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Sponsoring Units: GMAG DMP FIAP Chair: Hailong Wang, Penn State University Room: 394 |
Tuesday, March 14, 2017 2:30PM - 3:06PM |
H47.00001: Spin Seebeck, anomalous Nernst, and magnetic proximity effects in non-magnet/magnet heterostructures Invited Speaker: Timo Kuschel The spin Seebeck effect (SSE), the thermal generation of spin currents, is one of the most fascinating spin caloric phenomena. While the transverse SSE has been strongly discussed in the community [1], the longitudinal SSE (LSSE) in magnetic insulators detected by several groups is quite robust [2]. It has been shown for magnetic insulators, that magnetic proximity effects (MPEs) in the spin current detector material Pt do not hamper the spin caloric transport investigations [3]. Furthermore, alternative spin current detection techniques based on anomalous Hall effect [4] and magnetooptic Kerr effect in Au [5] have been performed recently. In my talk, I will give a brief introduction into the field of SSE and parasitic effects. I will further explain how we use x-ray reflectivity [6] to quantify MPEs in Pt and how these effects influences the SSE and parasitic effects. Finally, I will discuss the identification of the longitudinal SSE in magnetic conductors. [1] Meier, et al., Nat. Commun. 6, 8211 (2015); [2] Uchida et al., Proc. IEEE 104, 1946 (2016); [3] Miao et al., AIP Advances 6, 015018 (2016); [4] Hou et al., Nat. Commun. 7, 12265 (2016); [5] Kimling, et al. (2016), arXiv:1608.00702; [6] Kuschel et al., Phys. Rev. Lett. 115, 097401 (2015) [Preview Abstract] |
Tuesday, March 14, 2017 3:06PM - 3:18PM |
H47.00002: All-oxide spin Seebeck devices using RuO2 film depending on annealing temperature Akihiro Kirihara, Masahiko Ishida, Yuma Iwasaki, Hiroko Someya, Ryo Iguchi, Ken-ichi Uchida, Eiji Saitoh, Shinichi Yorozu The spin Seebeck effect (SSE) [1] has attracted great attention from both scientific and industrial viewpoints. An SSE-based thermoelectric (TE) device usually has a simple bilayer structure consisting of magnetic-insulator and metallic layers. For converting a SSE-induced spin current into an electric current, Pt has been typically used as the metallic layer because of its large inverse spin-Hall effect (ISHE). In this work, we show an all-oxide SSE device which adopts a conductive Ruthenium oxide (RuO$_2$) film instead of Pt. It was found that the sign and magnitude of the TE voltage appearing in the RuO$_2$ film is strongly dependent on the post-annealing temperature T$_{an}$, and when T$_{an}$ = 500$^{\circ}$C, the magnitude becomes larger than that using Pt. The result suggests that the ISHE property in RuO$_2$ is susceptible to its crystalline or electronic states, and can be optimally controlled via its formation processes. All-oxide SSE devices, having high material stability, will be promising for various useful applications such as heat-flow sensing [2]. [1] K. Uchida, et al., Nature 455, 778 (2008) [2] A. Kirihara, et al., Sci. Rep. 6, 23114 (2016) [Preview Abstract] |
Tuesday, March 14, 2017 3:18PM - 3:30PM |
H47.00003: Temperature Dependence of the Time-resolved spin-Seebeck Effect: Role of Bulk Magnon Diffusion John Jamison, Zihao Yang, Brandon Giles, Roberto Myers We present temperature dependent measurements of the time domain waveform of the spin-Seebeck (SSE) effect in platinum/ yttrium iron garnet (Pt/YIG) bilayers. A transient thermal gradient is generated in Pt/YIG by a modulated 980nm laser. The laser, with a rise time of 2 ns is focused onto the Pt surface where it generates a thermal gradient. The thermal gradient generates a flux of spin across the Pt/YIG interface where it is detected as a transverse voltage via the inverse spin Hall effect (ISHE). Using an oscilloscope, we measure the rise and fall times of the ISHE voltage as a function of temperature from 20 to 300 K. The modulation frequency of the laser is such that the ISHE signal is fully saturated, reaching quasi-steady state during the laser pulse, in order to fully capture the rise and fall time. Time domain, 3-D finite element modeling via COMSOL Multiphysics is carried out for the real sample. We correlate the observed time scales in the ISHE signal with materials properties in the Pt/YIG system, wherein the slow rise times are interpreted as diffusion of magnons from the bulk of YIG. Work supported by ARO MURI W911NF-14-1-0016. [Preview Abstract] |
Tuesday, March 14, 2017 3:30PM - 3:42PM |
H47.00004: Ab initio study of renormalized phonon modes in magnetic materials Matthew Heine, Olle Hellman, Nina Shulumba, David Broido Understanding the temperature dependent vibrational properties of magnetic materials in the presence of disordered local moments is a challenging problem. In such materials, the spin-spin interactions between neighboring magnetic atoms augment the usual electrostatic interactions thereby modifying the phonon spectra. To investigate such behavior, we apply a theoretical approach based on the Temperature Dependent Effective Potential (TDEP) method [1] to study the interdependence between the atomic and magnetic degrees of freedom in magnetic materials. In the framework of density functional theory we calculate the renormalized phonon dispersions at different temperatures, using the TDEP approach, sampling the appropriate thermally-relevant phase space. Results for several magnetic materials will be presented and compared to available measured data. [1] Olle Hellman, Peter Steneteg, I. A. Abrikosov, and S. I. Simak, Phys. Rev. B 87, 104111 (2013). [Preview Abstract] |
Tuesday, March 14, 2017 3:42PM - 3:54PM |
H47.00005: Theory of generation of angular momentum of phonons by heat current and its conversion to spins Masato Hamada, Shuichi Murakami Spin-rotation coupling in crystals will enable us to convert between spin current and mechanical rotations, as has been studied in surface acoustic waves, in liquid metals, and in carbon nanotubes. In this presentation we focus on angular momentum of phonons. In nonmagnetic crystals without inversion symmetry, we theoretically demonstrate that phonon modes generally have angular momenta depending on their wave vectors. In equilibrium the sum of the angular momenta is zero. On the other hand, if a heat current flows in the crystal, nonequilibrium phonon distribution leads to nonzero total angular momentum of phonons. It can be observed as a rotation of crystal itself, and as a spin current induced by these phonons via the spin-rotation coupling. [Preview Abstract] |
Tuesday, March 14, 2017 3:54PM - 4:06PM |
H47.00006: Magnon-phonon drag induced in a paramagnet Arati Prakash, Jack Brangham, Sarah Watzman, Fengyuan Yang, Joseph Heremans Recent theory predicts nonlocal magnon drag in a ferromagnetic bilayer, where magnetic current in one material induces a chemical potential in the neighboring material. [1] This inspires the possibility of inducing magnon drag from a temperature gradient on a ferromagnet into an adjacent paramagnet. To explore this concept, we compare the thermopower of Pt films grown on ferrimagnetic Y$_{\mathrm{3}}$Fe$_{\mathrm{5}}$O$_{\mathrm{12}}$ (YIG) to that grown on paramagnetic Gd$_{\mathrm{3}}$Ga$_{\mathrm{5}}$O$_{\mathrm{12}}$ (GGG). To isolate the hypothetical drag contribution from the magnons in YIG into the adjacent Pt film, we design a thermocouple using a hybrid sample with half GGG/Pt and half GGG/YIG(250nm)/Pt. The 6-nm Pt film is a rectangular U with one arm on YIG and the other on GGG. We measure the voltage between the arms of the U, while applying a temperature gradient parallel to the arms and perpendicular to the bottom connection. With a uniform applied temperature gradient, the Pt acts as a differential thermocouple. The effective voltage at the isothermal ends of the Pt is $\Delta $V $=$ ($\alpha_{\mathrm{YIG/Pt}}$ - $\alpha_{\mathrm{GGG/Pt}}$ )$\Delta $T. This provides a direct measure of the difference in thermopower of the two systems, which we attribute to magnon dynamics in YIG and their interactions at the YIG/Pt interface. We conduct thermopower measurements, investigating temperature dependence and in-field behavior. We repeat the experiment using Ag and Al instead of Pt, and varied YIG crystal orientation. [1] T. Liu, et al. Phys. Rev. Lett. 116, 237202 (2016) [Preview Abstract] |
Tuesday, March 14, 2017 4:06PM - 4:18PM |
H47.00007: Ballistic low-temperature magnon heat conduction in the helimagnetic insulator Cu$_2$OSeO$_3$ Narayan Prasai, Artem Akopyan, Sunxiang Huang, Joshua L. Cohn, Benjamin Trump, Guy G. Marcus, Tyrel M. McQueen We report on the observation of magnon thermal conductivities $\kappa_m\sim 80$~W/mK near $T=5$~K in single crystals of the helimagnetic insulator Cu$_2$OSeO$_3$, exceeding those observed previously in any other ferro- or ferrimagnet by almost two orders of magnitude. Distinguished in applied magnetic field, both magnon and phonon thermal conductivities exhibit ballistic behavior below 1K, with mean free paths limited by specimen boundaries. Changes in $\kappa_m$ through the helical-conical and conical-collinear spin-phase transitions with increasing applied field will also be discussed. [Preview Abstract] |
Tuesday, March 14, 2017 4:18PM - 4:30PM |
H47.00008: Low-temperature spin-Seebeck effect in the helimagnetic insulator Cu$_2$OSeO$_3$ Artem Akopyan, Narayan Prasai, Sunxiang Huang, Joshua L. Cohn, Benjamin Trump, Guy G. Marcus, Tyrel M. McQueen We report on measurements of the longitudinal spin-Seebeck effect in single crystals of the helimagnetic insulator Cu$_2$OSeO$_3$ in the range $0.5 {\rm K} \leq T\leq 15 {\rm K}$, using sputtered Pt thin films for spin-current detection. Simultaneous determination of magnon thermal conductivities for each specimen allows for a ``calibration'' of the spin current. The influence on the inverse spin-Hall signal of the helical-conical and conical-collinear magnetic phase transitions as well as different crystallographic orientations for the heat flow and applied magnetic field, will be discussed. [Preview Abstract] |
Tuesday, March 14, 2017 4:30PM - 4:42PM |
H47.00009: How to control spin-Seebeck current in a metal-quantum dot-magnetic insulator junction. Hua-Hua Fu, Lei Gu, Ruqian Wu The control of the spin-Seebeck current is still a challenging task for the development of spin caloritronic devices. Here, we construct a spin-Seebeck device by inserting a quantum dot (QD) between the metal lead and magnetic insulator. Using the slave-particle approach and noncrossing approximation, we find that the spin-Seebeck effect increases significantly when the energy level of the QD locates near the Fermi level of the metal lead due to the enhancement of spin flipping and occurrences of quantum resonance. Since this can be easily realized by applying a gate voltage in experiments, the spin-Seebeck device proposed here can also work as a thermovoltaic transistor. Moreover, the optimal correlation strength and the energy level position of the QD are discussed to maximize the spin-Seebeck current as required for applications in controllable spin caloritronic devices. [Preview Abstract] |
Tuesday, March 14, 2017 4:42PM - 5:18PM |
H47.00010: Spinon and Phonon Seebeck Effects Invited Speaker: Eiji Saitoh Generation and utilization of a flow of spin angular momentum of electrons in condensed matter, called spin current, are the key challenge of today's nano-scale magnetism and spintronics. The discovery of the inverse spin Hall effect (ISHE) [1], the conversion of spin current into electric voltage via spin-orbit interaction, has allowed researchers to detect and utilize spin current directly, and, since then, many spin-current driven effects have been discovered by exploiting the ISHE. In my talk, I will give an introduction to the following topics: (1) Spin-Liquid spin current carried by spinons [2], (2) Phonon anomaly in spin Seebeck effects [3], and (3) Spin current coupled with mechanical motion [4], to discuss the general mechanism of spin-current interaction. [1] E. Saitoh et al., Applied Physics Letters 88 (2006) 182509. [2] D. Hirobe et al., Nature physics (2016) published online. [3] T. Kikkawa et al., Physical Review Letters 98 (2016) in press. [4] R. Takahashi et al., Nature physics 12 (2015) 52. [Preview Abstract] |
Tuesday, March 14, 2017 5:18PM - 5:54PM |
H47.00011: Observation of the Spin Nernst Effect in Platinum Invited Speaker: Sebastian Goennenwein Thermoelectric effects -- arising from the interplay between thermal and charge transport phenomena -- have been extensively studied and are considered well established. Upon taking into account the spin degree of freedom, however, qualitatively new phenomena arise. A prototype example for these so-called magneto-thermoelectric or spin-caloritronic effects is the spin Seebeck effect, in which a thermal gradient drives a pure spin current. In contrast to their thermoelectric counterparts, not all the spin-caloritronic effects predicted from theory have yet been observed in experiment. One of these `missing' phenomena is the spin Nernst effect, in which a thermal gradient gives rise to a transverse pure spin current. We have observed the spin Nernst effect in yttrium iron garnet/platinum (YIG/Pt) thin film bilayers. Upon applying a thermal gradient within the YIG/Pt bilayer plane, a pure spin current flows in the direction orthogonal to the thermal drive. We detect this spin current as a thermopower voltage, generated via magnetization-orientation dependent spin transfer into the adjacent YIG layer. Our data shows that the spin Nernst and the spin Hall effect in in Pt have different sign, but comparable magnitude, in agreement with first-principles calculations. [Preview Abstract] |
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