Spin transport in thick insulating antiferromagnetic films

Abstract

Spin transport of magnonic excitations in uniaxial insulating antiferromagnets (AFs) is investigated. In linear response to spin biasing and a temperature gradient, the spin transport properties of normal-metal-insulating antiferromagnet-normal-metal heterostructures are calculated. We focus on the thick-film regime, where the AF is thicker than the magnon equilibration length. This regime allows the use of a drift-diffusion approach, which is opposed to the thin-film limit considered by Bender et al. 2017, where a stochastic approach is justified. We obtain the temperature-and thickness-dependence of the structural spin Seebeck coefficient S and magnon conductance G. In their evaluation we incorporate effects from field-and temperature-dependent spin conserving intermagnon scattering processes. Furthermore, the interfacial spin transport is studied by evaluating the contact magnon conductances in a microscopic model that accounts for the sub-lattice symmetry breaking at the interface. We find that while inter-magnon scattering does slightly suppress the spin Seebeck effect, transport is generally unaffected, with the relevant spin decay length being determined by non-magnon-conserving processes such as Gilbert damping. In addition, we find that while the structural spin conductance may be enhanced near the spin flip transition, it does not diverge due to spin impedance at the normal metal-magnet interfaces.

All‐Electrical Magnon Transport Experiments in Magnetically Ordered Insulators

“…After the first theoretical prediction and experimental demonstration of all-electrical magnon transport in NM/MOI heterostructures, [61][62][63] experiments in this regard were conducted not only in ferri-MOIs [23,[64][65][66][67][68][69][70][72][73][74][75][76]181,223,224] but also in AFIs. [71,[77][78][79][80]171] In this way, we obtained access to studying magnon transport, corresponding to GHz or even THz frequencies, utilizing magnetotransport techniques and DC charge currents.…”

“…Several groups have already made tremendous contributions toward a better understanding of all-electrical magnon transport experiments in MOIs. [64][65][66][67][68][69][70][71][72][73][74][75][76][77][78][79][80] These experiments utilize a heterostructure consisting of two NM strips in contact with the MOI, as shown in Figure 2. In the experiment, a charge current density j q is applied to the NM injector strip, which generates a spin current density j s .…”

“…[23,68] In the following sections we assume the case for two sublattice AFIs with the two magnon modes α and β carrying opposite spin momentum of AE ℏ. [23,31,76,159] In this way, we can consider spin current transport in AFIs as the magnonic analogue of electron spin transport, where also two opposing spin directions contribute. In case of AFIs, the spin direction of the two magnon modes is collinear to the orientation of the Néel vector.…”

Magnon spin transport around the compensation magnetic field in easy-plane antiferromagnetic insulators

“…where ρ k is defined as a 2 × 2 magnon density matrix and the collision integral I k should include all relevant, not only elastic but also inelastic, scattering processes [23,32,[34][35][36][37][38][39]. By taking into account the large splitting between the two spin bands, the density matrix and Eq.…”

Antiferromagnetic spin Seebeck effect across the spin-flop transition: A stochastic Ginzburg-Landau simulation

“…The SSE has recently been extended to insulating antiferromagnets such as Cr 2 O 3 [19], MnF 2 [20], NiO [21], α-Cu 2 V 2 O 7 [22], and FeF 2 [23]. This AF SSE offers a nice playground to investigate the interplay of spin current and antiferromagnetism [24][25][26][27].…”