Variation of exchange interactions and magnetism with uniaxiality in MnAs thin films

The magnetic behavior of high quality MnAs thin films grown on GaAs(100) substrates by means of molecular beam epitaxy has been studied. The correlation between structural parameters such as film strain and orientation distribution of the MnAs hexagonal unit cell and the magnetic anisotropy and the ferromagnetic ordering temperature has been investigated. Uniaxialy oriented and relaxed films display a transition temperature (T$_{c}$) and anisotropy constants (K$_{1}$/K$_{2}$) close to bulk MnAs values while strained MnAs films show T$_{c}$) and K$_{1}$/K$_{2}$ values clearly deviating from the corresponding bulk values. The experimental findings from magnetic (SQUID magnetometry), structural (XRD) and element specific magnetic (X-ray magnetic circular dichroism) measurements have been complemented by theoretical calculations (full potential linearized muffin tin orbital method in the local spin density approximation) of the change of exchange and anisotropy energies with strain in the unit cell.