Spin Seebeck effect in the polar antiferromagnet α−Cu2V2O7

Abstract

We have studied the longitudinal spin Seebeck effect in a polar antiferromagnet α-Cu2V2O7 in contact with a Pt film. Below the antiferromagnetic transition temperature of α-Cu2V2O7, spin Seebeck voltages whose magnetic field dependence is similar to that reported in antiferromagnetic MnF2|Pt bilayers are observed. Though a small weak-ferromagnetic moment appears owing to the Dzyaloshinskii-Moriya interaction in α-Cu2V2O7, the magnetic field dependence of spin Seebeck voltages is found to be irrelevant to the weak ferromagnetic moments. The dependences of the spin Seebeck voltages on magnetic fields and temperature are analyzed by a magnon spin current theory. The numerical calculation of spin Seebeck voltages using magnetic parameters of α-Cu2V2O7 determined by previous neutron scattering studies reveals that the magnetic-field and temperature dependences of the spin Seebeck voltages for α-Cu2V2O7|Pt are governed by the changes in magnon lifetimes with magnetic fields and temperature.Low-dimensional quantum magnets have attracted much attention in condensed matter physics for many decades [1,2]. It is known that in a one-dimensional antiferromagnetic system, long-range ordering is absent even at zero temperature [3], leading to exotic magnetic ground states, e.g. quantum spin liquid states [4]. Spin excitations in spin liquid states are spinons, which are regarded as spin-1/2 excitations as opposed to spin-1 excitations of magnons. Very recently, spin currents carried by spinons were demonstrated experimentally using the spin Seebeck effect (SSE) in Sr 2 CuO 3 |Pt systems [5]. Unusual magnetic properties of low-dimensional quantum magnets are intriguing for the search of new spin current effects.Among various compounds, a copper divanadates α-Cu 2 V 2 O 7 is a low-dimensional antiferromagnetic spin-1/2 system with fascinating magnetic properties. The oxide compound Cu 2 V 2 O 7 crystallizes in dichromate structure with three different polymorphs, i.e. α, β, and γ phases [6]. The structures of the β and γ phases are centrosymmetric, while the α phase possesses a noncentrosymmetric crystal structure with a polar point group (mm2) [6,7]. The space group of α-Cu 2 V 2 O 7 is F dd2 with lattice constants of a = 20.645Å, b = 8.383Å, and c = 6.442Å [8]. As illustrated in Fig. 1(a), all Cu 2+ ions form two sets of almost perpendicular zigzag chains [6][7][8][9].Magnetic properties of α-Cu 2 V 2 O 7 are governed by Cu 2+ S = 1/2 spins, since V 5+ ions are nonmagnetic. In the proposed spin Hamiltonian [10], there are three important terms to explain the magnetic properties of α-Cu 2 V 2 O 7 . The first term is isotropic exchange interactions. In the zigzag spin chains, Cu 2+ spins interact with their nearest neighbors. Since the magnetic interactions between nearest (J 1 ), second-nearest (J 2 ), and third-nearest (J 3 ) neighbors are all antiferromagnetic [6-10], α-Cu 2 V 2 O 7 exhibits antiferromagnetism. The second term is an anisotropic exchange interaction, which arises from the multiorbital correlation effect [10]. ...

Laser control of magnonic topological phases in antiferromagnets

“…[70] where the gradient of a nonequilibrium magnonic spin chemical potential [65,[71][72][73][74][75] plays the role of an effective magnetic field gradient. Thereby we expect that the magnonic WF law [9,14,28] can be experimentally confirmed [55,69,70,[76][77][78][79][80][81][82][83][84][85].…”

Spin transport in thick insulating antiferromagnetic films

“…Their exceptional transport properties, as well as those reported in Refs. [7][8][9][10][11], are governed by the spin conductance and spin Seebeck coefficients. Rezende et al [27] discussed theoretically the spin Seebeck effect in AFs in contact with a normal metal.…”

Intrinsic spin Nernst effect of magnons in a noncollinear antiferromagnet

“…At the same time, magnons exhibit rich and fascinating physics associated with the topology of magnonic bands, e.g., the thermal Hall effect has been observed in collinear ferromagent Lu 2 V 2 O 7 [19]. The spin Nernst effect [20,21], akin to the spin Hall effect [22], can also be realized in magnon systems [4,[23][24][25][26][27].…”

“…Many spintronics concepts also apply to antiferromagnets [28]. In particular, collinear antiferromagnets can exhibit the spin Seebeck effect [29], spin pumping [30], spin-orbit torque [31], spin Nernst effect [23][24][25][26][27], etc.. Noncollinear antiferromagnets can provide an even richer playground for studies of topological properties where, for example, the topology of electron bands can result in the anomalous Hall effect [32]. Furthermore, spin polarized currents carried by electrons can be excited in noncollinear antiferromagnets [33].…”