Low-temperature characterization of the magnetic properties of MnBiAl thin films

The magnetic properties of thin-film samples of MnBi0.8Alx with aluminum concentrations of x = 0.0, 0.4, 0.6, and 0.8 were systematically studied over a temperature range of 20 to 300 K. The as-deposited films are amorphous and nonmagnetic, but highly textured polycrystalline films that are ferromagnetic are formed by annealing at 350 °C. Our measurements show that the coercivity of such films rapidly decreases, then approaches a constant value (4 kOe for x = 0.4) with increasing annealing time. Magnetic measurements show that both anisotropy and coercivity decrease with decreasing temperature. Unlike bulk MnBi, our MnBi0.8Alx thin films do not have a spin reorientation transition at low temperatures. This may be due to impediment of the lattice contraction by the Al atoms doped into the interstitial sites of the MnBi lattice