Magnetic phases and anisotropy in Gd-doped GaN

In this work we present a detailed study of the magnetic properties of GaN:Gd layers with different Gd content (6x10(15) to 1x10(19) cm(-3)) grown by reactive molecular beam epitaxy. The temperature dependence of the magnetic properties suggests the existence of at least two ferromagnetic phases with different order temperatures. The coexistence of two ferromagnetic phases is explained within the framework of the phenomenological model, introduced previously by Dhar [Phys. Rev. Lett. 94, 037205 (2005)]. The layers are also found to exhibit a magnetic anisotropy, with the hard axis along the growth direction and an easy plane parallel to the surface. Moreover, the saturation magnetization shows a dependence on the orientation of the magnetic field, which may result from the anisotropy in the polarization induced in the GaN matrix by the internal and external magnetic fields.