Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Y56: Thermal Spin Transport and ThermomagneticsRecordings Available
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Sponsoring Units: GMAG DMP FIAP Chair: Daryoosh Vashaee, North Carolina State U Room: Hyatt Regency Hotel -Burnham |
Friday, March 18, 2022 8:00AM - 8:12AM |
Y56.00001: Observation of the spin Seebeck effect in a paramagnetic insulator VO2 Renjie Luo, Liyang Chen, Xuanhan Zhao, Douglas Natelson, Henry Navarro, Ivan K Schuller The spin Seebeck effect (SSE) involves the generation of spin current in the presence of a temperature gradient across the material. Here we present a systematic study of the transverse SSE in the paramagnetic insulating phase of VO2 at low temperatures. In the nonlocal geometry, the spin current is thermally generated by an AC current flowing in one Pt wire and the SSE is detected by another Pt wire using a lock-in amplifier at the second harmonic via the inverse spin Hall effect. The pronounced SSE at 3 K, decreases sharply as the temperature increases to 10K, and suddenly changes sign at 15 K, before vanishing above about 40 K. The SSE shows the expected angle dependence with the in-plane field; however, when the field is out-of-plane, the signal is accompanied by a Nernst effect contribution. We will also discuss the dependence of the observed SSE on heater-detector distance. |
Friday, March 18, 2022 8:12AM - 8:24AM |
Y56.00002: Magnon shot noise in a longitudinal spin Seebeck device Douglas Natelson, Xuanhan Zhao, Liyang Chen, Renjie Luo, Changjiang Liu, Deshun Hong, Anand Bhattacharya If an angular momentum current in a magnetic insulator is carried by discrete magnons, each with angular momentum ℏ, there is expected to be a fundamental angular momentum current noise analogous to charge shot noise. In the spin Seebeck effect (SSE), an angular momentum current is driven by a temperature gradient, and this may be detected with a Pt wire through the inverse spin Hall effect (ISHE). In a longitudinal SSE structure based on a yttrium iron garnet film/gadolinium gallium garnet substrate, at low temperatures in addition to the spin Seebeck voltage we measure the voltage noise in the ISHE. We find an additional magnetic field-dependent component of the noise when the field is oriented to produce a non-zero spin Seebeck voltage. We compare this noise with rough theoretical estimates for a possible magnon shot noise detected via the ISHE. |
Friday, March 18, 2022 8:24AM - 8:36AM |
Y56.00003: Longitudinal spin Seebeck effect in thulium iron garnet (TmIG) thin films Amit Chanda, Christian Holzmann, Johannes Seyd, Manfred Albrecht, Manh-Huong Phan, Hariharan Srikanth The longitudinal spin Seebeck effect (LSSE) induces incoherent magnon excitations with the application of a temperature gradient across the thickness of a magnetic material. To avoid the mixing of the thermally generated pure spin current with the electronic degrees of freedom, magnetic insulators are preferred for LSSE. Although the ferrimagnetic insulator Y3Fe5O12 is known as the benchmark system for LSSE, other members of the insulating iron garnet family, e.g. the ferrimagnet Tm3Fe5O12 (TmIG) are of interest and have received less attention from the point of view of spin-caloritronics. We have performed a systematic investigation of LSSE in the TmIG/Pt bilayer for two different TmIG thicknesses: 236 and 89 nm. We found that the temperature dependence of the LSSE signal shows a sudden decrease below 200 K for both the films, which coincides with the sudden drop in the temperature dependence of saturation magnetization (MS). This anomalous drop in both MS and LSSE voltage can be interpreted in terms of spin reorientation caused by increase in the effective magnetic anisotropy as revealed independently in radio frequency transverse susceptibility experiments. Our findings will help in understanding the influence of spin reorientation on the LSSE in other insulating garnets. |
Friday, March 18, 2022 8:36AM - 8:48AM |
Y56.00004: Spin fluctuation induced spin Seebeck effect near the Neel temperature in antiferromagnetic thin films Josiah Keagy, Wei Yuan, Yawen Liu, Jing Shi It is believed that spin fluctuations in antiferromagnetic (AFM) films can enhance the transmission of spin current originating from ferrimagnetic (FM) insulators in the FM/AFM heterostructures. On the other hand, spin fluctuations alone are a source of spin current around the Neel temperature TN as demonstrated in FeF2. To further investigate this effect, we have studied the spin Seebeck effect (SSE) responses of YIG(110)/Cr2O3 and Cr2O3 devices epitaxially grown by pulsed laser deposition. In the former type of devices, we observe clear SSE peaks with peak temperatures relying on the Cr2O3 thicknesses, which could be interpreted by the enhanced spin current from YIG through Cr2O3. However, in the latter type, we also find an SSE peak at ~305 K in 80 nm thick Cr2O3 film, close to the TN of bulk Cr2O3 crystals. The peak broadens and shifts towards lower temperatures as the magnetic field increases. These results indicate that the observed SSE peaks in both types of devices are likely from the critical fluctuations in the vicinity of TN. Due to the challenge to measure AFM responses in thin films, our results not only reveal a possible mechanism of enhanced SSE signals in FM/AFM heterostructures, but also provide a novel way of probing spin fluctuations and determining TN. |
Friday, March 18, 2022 8:48AM - 9:00AM |
Y56.00005: Microscopic study of the spin Seebeck effect in YIG with resonant inelastic x-ray scattering Yanhong Gu, Jiemin Li, Jonathan Pelliciari, Valentina Bisogni The SSE in insulating Y3Fe5O12 (YIG) was discovered in 2010, defining it as a spin-wave-based transport effect generated by applying a temperature gradient [1]. Since then a multitude of transport studies have been reported indicating the temperature and thickness dependence, and the effect of magnetic field on SSE [2-3]. From a theoretical perspective, many models have been built to explain the experimental results [4-6]. However, no consensus has been reached on the mechanism behind the SSE in YIG; this is due to the lack of a suitable microscopic probe compatible with temperature gradient conditions and sensitive to the elementary excitations leading the transport. |
Friday, March 18, 2022 9:00AM - 9:12AM |
Y56.00006: Spin Seebeck effect in the multifunctional ferrimagnet Ga0.6Fe1.4O3 Juan-Carlos Rojas-Sanchez, Alberto Anadon, Elodie Martin, Suvidyakumar Homkar, Benjamin Meunier, Heloise Damas, Christophe Lefevre, Francois Roulland, Carsten Dubs, Olivier Copie, Rafael Ramos, Daniele Preziosi, Nathalie Viart, Sebastien Petit-Watelot Thermo-spin current generation in Ga0.6Fe1.4O3 (GFO)/Pt are shown. The spin Seebeck performance of this system is comparable with the widely used yttrium iron garnet, likewise to what we have observed in spin Hall magnetoresistance. We also rule out the possibility of a dominant proximity effect in the thermo-spin voltage by exploring the different magnetoresistive effects in the bilayer1. In addition, by fabrication of thermo-spin devices with controlled dimensions, we are able to accurately quantify the relevant parameters of the thermal effects, obtaining more accurate and comparable values for the spin Seebeck coefficient2. |
Friday, March 18, 2022 9:12AM - 9:24AM |
Y56.00007: Origins of transverse voltages generated by applied thermal gradients and applied electric fields in ferrimagnetic-insulator/heavy-metal bilayers Rakshit Jain, ARNAB BOSE, Jackson J Bauer, Robert A Buhrman, Caroline A Ross, Daniel C Ralph We compare thermal-gradient-driven transverse voltages in ferrimagnetic-insulator/heavy-metal bilayers (Tm3Fe5O12 /W and Tm3Fe5O12 /Pt) to corresponding electrically-driven transverse resistances at and above room temperature. We find for Tm3Fe5O12/W that the thermal and electrical effects can be explained by a common spin-current detection mechanism, the physics underlying spin Hall magnetoresistance (SMR). However, for Tm3Fe5O12 /Pt, this is not the case – the ratio of the electrically-driven transverse voltages (planar Hall signal/anomalous Hall signal) is much larger than the ratio of corresponding thermal-gradient signals, a result which is therefore very different from expectations for a SMR-based mechanism alone. We ascribe this difference to a proximity-induced magnetic layer at the Tm3Fe5O12/Pt interface. |
Friday, March 18, 2022 9:24AM - 9:36AM |
Y56.00008: Thermopower and Self-consistent Spin-Wave Theory for MnTe Morteza Jazandari, Jahanfar Abouie, Daryoosh Vashaee The experimental data indicate that thermopower increases dramatically due to magnon drag in antiferromagnetic Li-doped MnTe near the Néel temperature (TN). Also, thermopower sustains its high magnitude in temperatures above TN where a lack of magnons is expected. This behavior seems to exist due to the presence of short-range order (SRO) and correlation. Therefore, we calculated the thermopower versus temperature near and above TN by investigating magnetic order and correlation. The spin-wave theory (SWT) works well in magnetic materials at low temperatures, unlike at high temperatures where the theory fails to describe the SRO and correlations. To date, different approaches have been used for 2D, quasi 2D, and 3D systems such as variational method, boson mean-field theory, and modified SWT based on Dayson-Maleev representation for spin operators, all of which fail to provide the correct value of ordering temperature and behavior estimation near and above the TN. We show that considering the Baryakhtar-Krivoruchko-Jabelonski representation via bosons and pseudofermions in self-consistent SWT can describe the SRO above TN. The theoretical results are presented and benchmarked against the experimental data to justify the high-temperature thermopower. |
Friday, March 18, 2022 9:36AM - 9:48AM |
Y56.00009: Spin Seebeck effect in quantum magnet Pb2V3O9 Wenyu Xing, Ranran Cai, Kodai Moriyama, Kensuke Nara, YUNYAN YAO, Weiliang Qiao, Kazuyoshi Yoshimura, Wei Han Spin Seebeck effect, the generation of spin current from heat, has been extensively studied in a large variety of magnetic materials, including ferromagnets, antiferromagnets, paramagnets, and quantum spin liquids. In this paper, we report the study of the Spin Seebeck effect in the single crystalline Pb2V3O9, a typical spin-gapped quantum magnet with quasi-one-dimensional spin-1/2 chain. Detailed temperature and magnetic field dependences of the Spin Seebeck effect are investigated, and the temperature-dependent critical magnetic fields show a strong correlation to the Bose-Einstein condensation phase of the quantum magnet Pb2V3O9. This work shows the potential of using spin current as a probe to study the spin correlation and phase transition properties in quantum magnets. |
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