Ferromagnetic resonance driven by current-induced torque in uniform ferromagnetic micro-structures

We show that the recently demonstrated current induced torque (CIT) [A. Chernyshov, et al. Nat. Phys. 5, 656 (2009)] can excite magnetisation dynamics in micro-bars of uniform ferromagnetic semiconductors. Due to the combined effects of the spin-orbit and exchange interactions, a microwave current injected into (Ga,Mn)As (or (Ga,Mn)(As,P)) micro-bars generates an oscillating effective magnetic field. By using a sensitive electrical detection technique, we accurately measure the magnitude and direction of driving fields for samples under different strain. We confirm the observation of a field with the symmetry of the Dresselhaus spin-orbit interaction and observe an additional field with the symmetry of the Rashba spin-orbit interaction. Our work demonstrates a new scalable FMR technique which provides a sensitive method to study the nature of current-induced torques and to perform magnetic characterisation of uniform ferromagnetic micro-structures.