Effect of a magnetic field on the magnetostructural phase transition of MnAs films on GaAs

Abstract

We present a systematic investigation of the effect of an external magnetic field on the first order structural (hexagonal/orthorhombic) and magnetic (ferromagnetic/paramagnetic) phase transition of MnAs films grown epitaxially on GaAs(001). The experimental results obtained using x-ray diffraction, magneto-optical Kerr effect, and SQUID magnetometry clearly show two magnetic field regimes where the temperature evolution of the magnetic and structural macroscopic properties of the films exhibit different behavior near the phase transition. The different evolution of the magnetic and structural properties fades away when an external magnetic field larger than $1\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$ is applied along the easy magnetization axis. These results are attributed to two effects induced by the external magnetic field. The first one is the field-induced phase transition, similar to that reported in MnAs bulk. The second one, which dominates for fields below $1\phantom{\rule{0.3em}{0ex}}\mathrm{kOe}$, is attributed to the effect of the geometry of the microstructured domains formed during the phase transition on the macroscopic magnetic properties of the film. As a result, the changes in the magnetic properties detected by macroscopic measurements take place at temperatures lower than those observed by structural measurements, even though structural and magnetic phase transitions must occur simultaneously.