COMPOSITION DEPENDENCES OF KERR ROTATIONS IN MNBI AND MNBIAL FILMS

Composition dependences of MnBi and Al-doped MnBi films have been investigated. It has been found that the crystal growth and Kerr rotation theta(K) of MnBi depend sensitively on the composition ratio Mn/Bi. The optimum ratio is 55/45, where a strong c-axis orientation and a sharp peak in theta(K) appear. The maxiMUM theta(K) is 1.6-1.7-degrees at a wavelength of 700 nm at room temperature for glass substrates, and scarcely changes after doping with Al below 10%, but it decreases rapidly because the growth of MnAl becomes dominant when the Al content exceeds 10%. Doping with small amounts of Al is believed to obstruct the growth of the MnBi crystal and therefore results in a reduction in grain size.