Thermally induced fluctuations of spin accumulation in lateral spin-valve structures and impact on noise

Gradient of spin accumulation in spintronic devices such as lateral spin-valves allows to generate pure spin-current without charge-current. Spin accumulation is an out-of-equilibrium magnetization in which thermal fluctuations can occur. These fluctuations may constitute a source of noise in lateral spin-valve structures. In this study, the thermally induced fluctuations of the vector of spin-accumulation were investigated theoretically in diffusive regime. It is shown that paramagnetic resonance may arise in the spin-current carrying channel due to electron-electron interactions and exchange splitting induced by the spin-accumulation. This leads to an effect that was not previously considered: resonant increase of the magnetic susceptibility of the paramagnetic channel material and an associated decrease in signal-to-noise ratio around the resonance frequency. Frequency dependence of the magnetic susceptibility and signal-to-noise ratio were calculated analytically in the case of a specific T-shaped lateral spin-valve structures. It was shown however that this noise caused by thermally induced fluctuations in spin-accumulation is generally negligible in comparison to other sources of noise present in lateral spin-valves such as Johnson noise or thermal fluctuations of magnetization in the magnetic electrodes.