Crystal Structure and Magnetic Properties of MnBiAI Films

The properties of MnBiAl films prepared by alternately depositing, using vacuum evaporation, Mn and Bi layers with a single Al layer at the center, were studied. On annealing at temperatures between 230 and 420°C, films with Mn contents between 40 and 70 at% and with an Al content below 15 at% became ferromagnetic, with the magnetization perpendicular to the film plane. Adding Al caused the size of crystallites in the film to decrease to about 50 nm, and acted to suppress phase transitions between the low (Itp) and high (htp) temperature phases. Such films did not differ significantly from MnBi films with regard to the crystal structure, lattice constants or Curie temperature. The Kerr rotation spectrum had a maximum value of 1.78° at about 700 nm, as well as a peak value of 1.5° at 370 nm. Film reflectivities varied from 40 to 60% in the wavelength range from 330 to 800 nm.