Crystal structure and magnetic properties of Cr-Doped AlN films with various Cr concentrations

We have studied the crystal structure and magnetic properties of Cr-doped AlN (Al_1-xCr_xN) films in the range of Cr concentration (x) of 0.04-0.37. The film changes from a wurtzite-type AlN phase for x = 0.04-0.20 to a wurtzite-type AlN phase and zinc-blende-type AlN mixed phase for x = 0.24, and further to only the zinc-blende-type AlN phase with increasing x. The Cr atoms are considered to occupy Al sites in spite of the change of AlN phase with x. Room-temperature (RT) ferromagnetism is not observed at any x. The magnetic state at 10 K of the film is considered to change from a paramagnetic state to a paramagnetic state or a superparamagnetic state, and further to a paramagnetic state as x increases. Ferromagnetic state is not observed at 10 K regardless of x.