Spin transport through a nanojunction with a precessing anisotropic molecular spin: Quantum interference and spin-transfer torque

The subject of this study is spin transport through a molecular orbital connected to two leads, and coupled via exchange interaction with a precessing anisotropic molecular spin in a constant magnetic field. The inelastic spin-flip processes between molecular quasienergy levels are driven by the molecular spin precession. By setting the Larmor frequency, the tilt angle of molecular magnetization with respect to the magnetic field, and the magnetic anisotropy parameter, one can modulate the spin current and noise, spin-transfer torque, and related torque coefficients. Moreover, the dc-spin current and spin-transfer torque components provide the quasienergy level structure in the orbital. Quantum interference effects between states connected with spin-flip processes manifest themselves as dips (minimums) and peaks (maximums) in spin-current noise, matching Fano-like resonance profiles with equal probabilities of interfering elastic and inelastic spin-flip pathways. By proper adjustment of the anisotropy parameter and magnetic field, the precession is suppressed and the torque vanishes, revealing the anisotropy parameter via a dc-spin current or torque measurement. The results of the study show that spin transport and spin-transfer torque can be manipulated by the anisotropy parameter even in the absence of the magnetic field.