Spin pumping from a ferromagnet into a hopping insulator: Role of resonant absorption of magnons

Abstract

Motivated by recent experiments on spin pumping from a ferromagnet into organic materials in which the charge transport is due to hopping, we study theoretically the generation and propagation of spin current in a hopping insulator. Unlike metals, the spin polarization at the boundary with ferromagnet is created as a result of magnon absorption within pairs of localized states and it spreads following the current-currying resistor network (although the charge current is absent). We consider a classic resonant mechanism of the ac absorption in insulators and adapt it to the absorption of magnons. A strong enhancement of pumping efficiency is predicted when the Zeeman splitting of the localized states in external magnetic field is equal to the frequency of ferromagnetic resonance. Under this condition the absorption of a magnon takes place within individual sites.

Theory of spin-coherent electrical transport through a defect spin state in a metal/insulator/ferromagnet tunnel junction undergoing ferromagnetic resonance

“…The emerging field of "quantum spintronics" seeks to engineer and manipulate single coherent spin systems for the sake of quantum-enhanced sensing/imaging technologies and quantum computing [1]. Defect spins in an insulating region between a ferromagnetic metal and a nonmagnetic conductor produce an array of coherent spin-dependent phenomena, including defect-associated spin pumping [2][3][4], thermal spin transport [5], and small-field magnetoresistance under electrical bias [6][7][8]. Individual spin-coherent defects have even been electrically detected in precisely-designed junctions [9,10].…”

Quantitative inverse spin Hall effect detection via precise control of the driving-field amplitude

“…As the magnitude of the ISHE response scales linearly with the strength of the MW radiation field [3][4][5][6][7][8], quantitative ISHE experiments which, for instance, are needed to test fundamental theories of charge free spin-injection into organic semiconductors [9] or the nature of spin transport in the latter [10], require a precise knowledge of the strength of the MW radiation amplitude B 1 . Most studies involving ISHE experiments derive B 1 from estimates that are based on the MW power applied to the resonator or waveguide structure.…”