Elastic and magnetic properties of epitaxial MnAs layers on GaAs

Abstract

We have investigated the elasto- and magneto-optical properties of MnAs layers epitaxially grown on (001) GaAs for temperatures around the structural (hexagonal/orthorhombic) and magnetic (ferromagnetic/paramagnetic) phase transition of MnAs at ${T}_{c}\ensuremath{\sim}40\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}.$ The phase transition is accompanied by a large variation of the MnAs lattice parameter a of $\ensuremath{\sim}1%,$ which induces a strong and anisotropic strain field in the MnAs/GaAs heterostructures. The latter was measured by detecting the optical anisotropy induced on the GaAs substrate by means of polarization-sensitive light transmission measurements. The experimental results show clear evidence for the quasi-uniaxial strain induced on the GaAs substrate during the phase transition, which extends over a temperature range of $\ensuremath{\sim}30\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ in the MnAs/GaAs heterostructures. The strain levels are well reproduced by an elastic model for the heterostructures which assumes that the strain is transferred across the MnAs/GaAs interface without relaxation. The elastic properties during the phase transition were compared to the average magnetization probed using a SQUID magnetometer and to the magnetization near the front and the back surfaces of the MnAs films detected using the magneto-optical Kerr effect. The smaller temperature range of the phase transition observed in the magneto-optical Kerr effect measurements indicates a lower stability of the ferromagnetic phase near the surface of the MnAs layers.