Coulomb blockade anisotropic magnetoresistance and voltage controlled magnetic switching in a ferromagnetic GaMnAs single electron transistor

Abstract

We observe low-field hysteretic magnetoresistance (MR) in a (Ga,Mn)As single electron transistor which can exceed three orders of magnitude. The sign and size of the MR signal is controlled by the gate voltage. Experimental data are interpreted in terms of electrochemical shifts associated with magnetization rotations. This Coulomb blockade anisotropic MR is distinct from previously observed anisotropic MR effects as it occurs when the anisotropy in a band structure derived parameter is comparable to an independent scale, the single electron charging energy. Effective kinetic-exchange model calculations in (Ga,Mn)As show chemical potential anisotropies consistent with experiment and ab initio calculations in transition-metal systems suggest that this generic effect persists to high temperatures in metal ferromagnets with strong spin–orbit coupling. In addition we observe a significant gate voltage dependence of the magnetic switching field which we attribute to carrier density variations in the electric field exposed GaMnAs regions causing a substantial change in the magneto-crystalline anisotropy profile.