Epitaxial MnAs films studied by ferromagnetic and spin wave resonance

We investigated the anisotropy and intrinsic exchange interaction within MnAs films using ferromagnetic resonance (FMR) and spin wave resonance (SWR), respectively. Apart from the dominating in-plane easy axis a presence of an independent contribution (independent FMR mode) characterized by an out-of-plane easy axis is found in agreement with our previous magnetometric studies. The temperature sweep of the resonance spectra shows a jump both for the resonance field and the resonance linewidth at a temperature of 10 degrees C, i.e., at the transition from the hexagonal (ferromagnetic) a-phase to the region of the coexisting alpha- and orthorhombic (paramagnetic) beta-phase. In the coexistence region the main easy axis lies in-plane and perpendicular to the stripe direction being the direction of the c axis. In the SWR measurements with magnetic field applied close to the normal of the film a set of lines resulting from the excitation of spin waves is observed. The extracted exchange constant is as small as A = 17.7 x 10(-10) erg/cm. Moreover, the temperature dependence of the spin wave stiffness constant D = 2A/M has been determined within the coexistence region.