A comparative study of Ni2MnGa, Ni2MnAl, and Ni2MnIn Heusler alloy films

Ni2MnGa, Ni2MnAl, and Ni2MnIn alloy films were fabricated by using a flash-evaporation technique. A wide substrate temperature range (from 150 K to 720 K) was chosen to prepare the alloy films with significantly different atomic ordering. Various physical properties, including optical properties, were investigated. It was found that the optical properties of the bulk alloys are very sensitive to the atomic ordering. Unexpectedly, the disordered alloy films are not ferromagnetically ordered. The Ni2MnAl bulk alloy exhibits a nonmagnetic behavior. Annealing of the disordered films restores the ordered structure with an almost full recovery of the magnetic and transport properties of the ordered films. These results were further discussed in connection with the atomic structures of the alloy films.