Spin-photonic, photonic and other relevant properties of Ni2MnGe and other Heusler alloys

Various physical properties for films of Heusler alloys, such as Ni2MnGe and Cu2MnAl, with different atomic orders were studied. The films were deposited on glass substrates at several substrate temperatures from 150 to 730 K. The structural characterization was performed by using X-ray diffraction. A superconducting-quantum-interference-device magnetometer was employed to measure the temperature dependence of the spin properties. The photonic and the spin-photonic properties were also investigated. Alloy films with corresponding L2(1)-type structural orders were successfully fabricated. The ordered films exhibited physical properties close to those of the corresponding bulk alloy. The significant effects of structural disorder on the photonic, the spin, and the spin-photonic properties were experimentally observed. Unexpectedly, the disordered Ni2MnGe alloy films were not ferromagnetically ordered. Atomic disordering led to the disappearance of the high-energy absorption peak in the optical-conductivity spectrum and to the lack of a spin-photonic response. All these results were further analyzed in connection with the electronic structures of the alloy.