Spin transport across antiferromagnets induced by the spin Seebeck effect

Abstract

For prospective spintronics devices based on the propagation of pure spin currents, antiferromagnets are an interesting class of materials that potentially entail a number of advantages as compared to ferromagnets. Here, we present a detailed theoretical study of magnonic spin current transport in ferromagnetic-antiferromagnetic multilayers by using atomistic spin dynamics simulations.The relevant length scales of magnonic spin transport in antiferromagnets are determined. We demonstrate the transfer of angular momentum from a ferromagnet into an antiferromagnet due to the excitation of only one magnon branch in the antiferromagnet. As an experimental system, we ascertain the transport across an antiferromagnet in YIG|Ir 20 Mn 80 |Pt heterostructures. We determine the spin transport signals for spin currents generated in the YIG by the spin Seebeck effect and compare to measurements of the spin Hall magnetoresistance in the heterostructure stack. By means of temperature-dependent and thickness-dependent measurements, we deduce conclusions on the spin transport mechanism across IrMn and furthermore correlate it to its paramagnetic-antiferromagnetic phase transition. arXiv:1803.03416v1 [cond-mat.mtrl-sci]

Unveiling domain wall dynamics of ferrimagnets in thermal magnon currents: Competition of angular momentum transfer and entropic torque

“…The classical spin-wave amplitudes for the uniaxial FI at T = 0 K can be calculated from LSWT, follow- ing Refs. [55,74] (see Appendix A). We find that the low-frequency branch (σ = −1) in the dispersion relation carries momentum parallel to m z A = +1 and the high-frequency branch (σ = +1) parallel to m z B = −1.…”

“…Following Refs. [55,74] one can deduce the linearized LLG-equation in k-space in analogy to the FM and AFM case:…”

Damping Enhancement in Coherent Ferrite–Insulating-Paramagnet Bilayers

“…Spin transport and enhanced damping through spin pumping 24 in ferrite/spin-orbit-metal structures has already been extensively studied 3,4,[12][13][14][15]25 . Moreover, the low-damping ferrite can be interfaced with an insulating antiferromagnetic or paramagnetic oxide, in which signals can be transmitted as a pure magnon spin current [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] . While interfacing low-damping ferrites with insulating anti/paramagnetic oxides has enabled prototypes of magnon spin valves [37][38][39] , the fundamental impact of insulating oxide interfaces on spin dynamics has remained mostly unexplored.…”

“…Moreover, the low-damping ferrite can be interfaced with an insulating antiferromagnetic or paramagnetic oxide, in which signals can be transmitted as a pure magnon spin current [26][27][28][29][30][31][32][33][34][35][36][37][38][39][40] . While interfacing low-damping ferrites with insulating anti/paramagnetic oxides has enabled prototypes of magnon spin valves [37][38][39] , the fundamental impact of insulating oxide interfaces on spin dynamics has remained mostly unexplored. In particular, it is an open question whether or how damping of the ferrite is enhanced from spin dissipation within the bulk of the adjacent anti/paramagnetic oxide or from spin scattering at the oxide interface.…”

Spin decoherence independent of antiferromagnetic order in IrMn

“…Such spin dephasing in AFMs generates a spin-transfer torque, ∝ l × s × l [13-15], which may be crucial for emerging antiferromagnetic spintronic technologies [16][17][18][19][20].Furthermore, spin dephasing in an AFM with a uniform Néel vector may yield anisotropic decoherence, where spin absorption by the AFM is enhanced when l ⊥ s [21].By contrast, polycrystalline thin films of AFMs by themselves do not exhibit anisotropic spin decoherence on a macroscopic scale, since the grains contain a distribution of Néel vector orientations that averages out the anisotropy [22]. While polycrystalline AFMs have found commercial applications (i.e., pinning ferromagnetic layers in spin valves) [23] and been used as spin sinks [8,22,[24][25][26][27][28], their nonuniform, unpinned antiferromagnetic order poses a challenge for gaining fundamental insight into spin decoherence.To align the global antiferromagnetic order, a polycrystalline AFM can be exchange-bias-coupled to a ferromagnetic metal (FM) [29][30][31]; the Néel vector l can be pinned along the direction of the bias field during film deposition or field cooling. In such exchange-biased polycrystalline FM/AFM bilayers, a recent spin pumping experiment has reported anisotropic relaxation of pure spin current in the AFM layer governed by dephasing, i.e., spin transfer acting on l [21].…”