Magnetic, Optical and Magneto-optical Properties of Ni$_{2}$MnGe Alloy Films

The influence of atomic ordering on the magnetic, the optical and the magneto-optical (MO) properties of Ni$_{2}$MnGe Heusler alloy (HA) films was investigated. The bulk Ni$_{2}$MnGe HA was prepared by arc melting, and the films were deposited by flash evaporation onto glass substrates at several substrate temperatures from 150 to 730 K. The bulk Ni$_{2}$MnGe HA exhibits the cubic $L$2$_{1}$ structure with $a$ = $b$ = $c$ = 0.5761 nm, and the annealed (at 573 K) bulk alloy is in the tetragonal structure with $a$ = $b$ = 0.5720 nm and $c$ = 0.5865 nm. While the films deposited at 720 K show a well-ordered $L$2$_{1}$ structure, the deposition at 150 K $< T <$ 710 K results in the formation of a nanocrystalline or an amorphous microstructure. It was found the structural disorder in Ni$_{2} $MnGe films induces lack of the ferromagnetic order and noticeable changes in the optical and MO response.