Shape of the Hanle curve in spin-transport structures in the presence of an ac drive

Resistance between two ferromagnetic electrodes coupled to a normal channel depends on their relative magnetizations. The spin-dependent component, R, of the resistance changes with magnetic field, B, normal to the directions of magnetizations. In the field of spin transport, this change, R(B), originating from the Larmour spin precession, is called the Hanle curve. We demonstrate that the shape of the Hanle curve evolves upon application of an ac drive and study this evolution theoretically as a function of the amplitude, B1, and frequency, ω, of the drive. If the distance between the electrodes, L, is smaller than the spin-diffusion length, λs , the prime effect of a weak circular-polarized drive is the shift of the center of the curve to the value of B for which the Larmour frequency, ωL, is ∼B2 1/ω. Magnetic resonance at ωL ∼ ω manifests itself in the derivative, dR dB. For large L λs the ac drive affects the Hanle curve if the drive amplitude exceeds the spin-relaxation rate, τ −1 s , i.e., at B1τs 1. The prime effect of the drive is the elimination of a minimum in R(B). A linearly polarized drive has a fundamentally different effect on the Hanle curve, affecting not its shape but rather its width.