Toroidal quantum states in molecular spin-frustrated triangular nanomagnets with weak spin-orbit coupling: Applications to molecular spintronics

Jared M. Crabtree and Alessandro Soncini
Phys. Rev. B 98, 094417 – Published 14 September 2018

Abstract

We theoretically investigate the ground-state spin texture and spin transport properties of triangular rings with on-site spins Sq=12(q=13). In the limit of strong antiferromagnetic exchange coupling and weak spin-orbit coupling, we find it is possible to prepare a noncollinear degenerate ground state with a zero magnetic moment and a nonzero toroidal moment τ=gμBqrq×Sq, aligned along the C3-symmetry axis. These pure toroidal states can be prepared: (i) within the fourfold degenerate spin-frustrated ground state even without any spin-orbit coupling; (ii) within the ground Kramers doublet resulting from weak spin-orbit splitting of the fourfold degenerate frustrated manifold via Dzyaloshinskii-Moriya antiferromagnetic exchange coupling. We also investigate the relationship between toroidal states and chiral spin states, characterized by the eigenvalues of the scalar spin chirality operator χ̂=43Ŝ1·Ŝ2×Ŝ3, and find that, since [τ̂,χ̂]0, it is not possible to prepare states that are both toroidal and chiral simultaneously. Finally, by setting up a quantum transport model in the Coulomb blockade regime, we find that a spin current injected through a spin-polarized source electrode into the triangle is partially reversed upon scattering with the molecular toroidal states. This spin-switching effect is, in fact, a signature of molecular spin-transfer torque, which can be harnessed to modify the nonequilibrium populations of the +τ- and τ-toroidal states, thus, to induce a net toroidal magnetization in the device using a spin current.

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  • Received 13 May 2018

DOI:https://doi.org/10.1103/PhysRevB.98.094417

©2018 American Physical Society

Physics Subject Headings (PhySH)

Quantum Information, Science & TechnologyAtomic, Molecular & OpticalCondensed Matter, Materials & Applied Physics

Authors & Affiliations

Jared M. Crabtree and Alessandro Soncini*

  • School of Chemistry, University of Melbourne, Parkville, Victoria 3010, Australia

  • *asoncini@unimelb.edu.au

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Issue

Vol. 98, Iss. 9 — 1 September 2018

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