Magnetic order and anisotropies of MnAs epitaxial layers

L.B. STEREN, J. MILANO, V. GARCIA, M. MARANGOLO, M. EDDRIEF, V.H. ETGENS

San Sebastian, España

Conferencia; III Joint European Magnetic Symposia; 2006

San Sebastian, España

Metallic MnAs is a promising material for uses in semiconductor-based spintronic devices. In fact, bulk MnAs is ferromagnetic at room temperature and has an hexagonal structure (alpha) whose lattice parameters match very well with those of GaAs. The MnAs undergoes a first order transition at T*=40 C between the low temperature hexagonal ferromagnetic phase and a paramagnetic orthorhombic one (beta). In this contribution, we present a study of the magnetic behaviour of MnAs epitaxial films grown on both, GaAs(111) and GaAs(100) substrates. Our research, performed by magnetization and ferromagnetic resonance (FMR) measurements, allow us to get a deep insight of the ordering of the Mn lattice and the anisotropies of the system. Previous results showed that the MnAs thin films properties are strongly affected by the substrate material and orientation [1].  In this work, we present new evidences about the coexistence of the alpha and beta phases below T*.  Moreover, we showed through FMR experiments that the alpha-phase is oriented perpendicular to the substrate surface for MnAs/GaAs(111) films while it lays along the substrate plane for MnAs/GaAs(100) ones. Also, a detailed study of the thermal and angle dependence of the films coercivity reveal the existence  of different activation mechanisms for domain movements in the samples. [1] A.K. Das et al., Phys. Rev. Lett. 91 (2003) 087203; N. Mattoso et al., Phys. Rev. B 70 (2004) 115324