Effect of disorder on various physical properties of Co2CrAl Heusler alloy films: Experiment and theory

We have investigated the effects of atomic disorder on the electronic structure and some physical properties of Co2CrAl Heusler alloy HA films. Flash evaporation onto glass substrates at different temperatures from 150 to 750 K and postannealing at various temperatures were employed to manipulate the structural order in Co2CrAl HA films. The L21-ordered Co2CrAl HA films exhibit the magnetic, the transport, and the optical properties close to those of the bulk ordered sample. Increase in the structural disorder L21 →B2 →A2 →amorphous state causes the reduction in the saturation magnetization and the Curie temperature TC down to the paramagnetic state for amorphous films. The recrystallization of amorphous Co2CrAl HA films is accompanied by an increase in resistivity by about 10%, which is interpreted to be related to the energy gap formation at the Fermi level for the minority bands in the L21 /B2-ordered state of Co2CrAl HA. The energyband structures of L21-ordered Co2CrAl HA have been calculated by using an all-electron full-potential linearized-augmented-plane-wave method. The optical and the magneto-optical properties of L21-ordered Co2CrAl HA have been experimentally investigated and explained in terms of the band structures. It was experimentally shown that the optical properties of crystalline L21 or B2-type ordered alloy at a temperature much higher than TC do not significantly change. Structural disorder in Co2CrAl HA from the crystalline to the amorphous state also does not radically alter the states responsible for the interband-absorption-peak formation.