Imaging in-plane 90° magnetization switching in a (Ga,Mn)As epitaxial layer

Abstract

The dynamics associated with in-plane, 90° magnetization switching in a (Ga,Mn)As epitaxial layer is studied on the basis of images obtained using a home-made magneto-optical microscope. A small contrast between two different 90° domains caused by magnetic birefringence (MB) is enhanced by digital image processing. Two consecutive 90° switchings are captured clearly in temperature regimes below and above the half-value of the Curie temperature. The dynamics is not the same for the first and the second switching, presumably reflecting the influence of the ⟨110⟩ uniaxial anisotropy and spin-dependent pinning sites. In particular, in the low-temperature regime, the first switching that passes via the relatively easy uniaxial (REU) axis (the [1–10] axis) is dominated by smooth 90° domain wall (DW) motion, whereas the second switching that passes via the relatively hard uniaxial (RHU) axis (the [110] axis) occurs through nucleation and coalescence of 90° domains together with the DW motion. In the high-temperature regime, the first switching via the REU axis is initiated by nucleations and their rapid expansion, whereas the second switching via the RHU axis is dominated by relatively slow DW motion. DW velocity is extracted from MB images and analyzed on the basis of thermally activated depinning and flow models. The values of two key parameters, namely, the activation volume and DW mobility, are deduced and compared with values from the literature. They are (28 nm)3 and 0.35 nm s−1 Oe at 10 K, respectively.