From ferro- to antiferromagnetism via exchange-striction of MnAs/GaAs(001)

We investigated the stress evolution in single-crystal MnAs films on GaAs(001) upon applying high external magnetic fields in the alpha/beta phase transition regime (10-40 degrees C) and beyond. Our stress measurements reveal large field-induced lattice distortions at temperatures, where beta-MnAs is present, even well above the phase transition (> 40 degrees C). A quantitative comparison with the field-induced increase of magnetization reveals that the changes in the lattice dimensions can be fully explained by the (reversible) back-transformation of beta-MnAs to alpha-MnAs. Our direction-dependent experiments identify the structural distortions at the phase transition as a volume magnetostriction effect and -due to the persisting magnetocrystalline anisotropy above 40 degrees C-strongly support an antiferromagnetic state for beta-MnAs.