Bulletin of the American Physical Society
APS March Meeting 2018
Volume 63, Number 1
Monday–Friday, March 5–9, 2018; Los Angeles, California
Session F25: Spin Current in AntiferromagnetsInvited
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Sponsoring Units: GMAG Chair: John Xiao, Univ of Delaware Room: LACC 403B |
Tuesday, March 6, 2018 11:15AM - 11:51AM |
F25.00001: Thermal magnonic spin current in antiferromagnetic insulator/YIG1 Invited Speaker: Chia-Ling Chien Pure spin current phenomena and devices are recent advents. A pure spin current has the attribute of delivering spin angular momentum with a minimal of charge carriers in a metal and no carriers in an insulator. Spin pumping and thermal injection are often used with a ferromagnetic (FM) material as a spin injector. However, FM metals are plagued by numerous parasitic effects, whereas more favorable conditions are afforded in FM insulators, such as Y3Fe5O12 (YIG), with which spin injection and detection can be unequivocally revealed. It has been recently reported that spin current generated in YIG can be enhanced by one order with a 1 nm antiferromagnetic (AF) NiO layer inserted between YIG and Pt [1, 2]. The spin current enhancement shows a maximum near the Néel temperature of the NiO layer, and is proportional to the spin mixing conductance at the normal metal/YIG interface [2]. Spin backflow from the AF insulator/YIG interface has been detected using the spin Hall magnetoresistance, showing a strong temperature dependence dominated by spin conductance [3]. These results demonstrate spin transport in AF insulators is dominated by incoherent thermal magnons and spin fluctuations. Temperature dependence of spin injection and other aspects will also be discussed. |
Tuesday, March 6, 2018 11:51AM - 12:27PM |
F25.00002: Temperature dependence of magnon transport Invited Speaker: Shufeng Zhang
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Tuesday, March 6, 2018 12:27PM - 1:03PM |
F25.00003: Spin current transport in an insulating antiferromagnet makes possible the observation of the spin Seebeck effect in permalloy separated from the anomalous Nernst effect Invited Speaker: Sergio Rezende The spin Seebeck effect (SSE) refers to the generation of a spin current by a temperature gradient in a magnetic material [1]. In the longitudinal configuration (LSSE) the SSE has been studied quatitatively only in magnetic insulators because in metallic films it is contaminated by the anomalous Nernst effect (ANE) [1]. We will present theoretical and experimental studies of the LSSE in the metallic ferromagnet N81Fe19 (permalloy-Py) separated from the ANE in trilayer samples of Py/NiO/NM (NM is a normal metal, Pt or Ta) under a temperature gradient perpendicular to the plane. The spin current due to SSE in Py that is transported across the NiO layer and reaches the NM layer, where it is converted into a charge current by the inverse spin Hall effect. The LSSE is detected by a voltage in the NM layer while the ANE is measured by the voltage induced in the Py layer. The separation of the two effects is made possible because the insulating AF layer of NiO transports spin current by magnon diffusion while providing electrical insulation between the Py and NM layers [2-5]. The measured spin Seebeck coefficient for Py has a value similar to the one for the ferrimagnetic insulator yttrium iron garnet, with the same sign, and is in good agreement with the value calculated with a thermoelectric spin diffusion model [6]. |
Tuesday, March 6, 2018 1:03PM - 1:39PM |
F25.00004: Spin transport in disordered materials via antiferromagnetic correlations Invited Speaker: Barry Zink Spin transport through ferromagnetic and antiferromagnetic (AF) insulators is an exciting new direction in spintronics. We have added a dramatic twist to this evolving picture by demonstrating long-distance spin transport in disordered magnetic insulators.[1] This work follows on recent electrical generation and detection of spin transport through the crystalline ferrimagnetic insulator yttrium iron garnet (YIG). These non-local transport experiments excite spin dynamics in the YIG via the spin Hall effect (SHE), and detect a spin current some distance away using the inverse spin Hall effect (ISHE). We have carried out similar experiments on amorphous YIG (a-YIG), a material with no long- or medium-range order (either structural or magnetic), and shown surprisingly long length-scale spin transport with measurable signals even for distances greater than 100 microns. Experiments on a-YIG supported both on a bulk substrate and on suspended Si-N membrane thermal platforms show that spin injection and transport does not require thermal gradients, but that the presence of in-plane thermal gradients enhances spin transport and reveals a large non-equilibrium spin thermal conductance. Among other intriguing aspects of this unexpected spin transport, we clarify that the effects are large not in a previously known low-temperature spin-glass state, but only at higher temperatures where only AF spin correlations are present. We will present recent further evidence of an origin of these results in spin transport, show similar effects in a second disordered magnetic material, and argue that the role of AF correlations is a more general feature that is seen even in spin transport through more structurally ordered systems. |
Tuesday, March 6, 2018 1:39PM - 2:15PM |
F25.00005: Electronic and magnonic spin current injection in fluctuating antiferromagnets Invited Speaker: Vincent Baltz In this talk, we will discuss the nature of a spin current flowing through fluctuating antiferromagnets and distinguish between electronic and magnonic spin transport. The method used to inject the spin currents involved ferromagnetic resonance and spin pumping in ferromagnetic-spin-injector / (non-magnetic-spin-conductor) / antiferromgnetic-spin-sink multilayers. Three typical cases will be presented, magnonic spin flow in the insulating antiferromagnets NiO and NiFeOx, electronic spin flow in the metallic antiferromagnet IrMn, and electronic and magnonic parallel spin flows in IrMn when the latter is directly exchange coupled to the ferromagnetic-spin-injector. In this latter case, how it is possible to unravel the spin injection efficiency of the two types of spin flows will be demonstrated, as well as how magnonic spin injection scales with the amplitude of the exchange coupling interactions. We will also demonstrate how linear spin fluctuations enhance spin injection in spin-sinks and show why this is pertinent to study critical phenomenon like magnetic phase transitions in ultra-thin films. To show the far-reaching practical relevance of the method, extension to various phase transitions will also be presented. |
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