Optical, magneto-optical, and magnetic properties of stoichiometric and off-stoichiometric γ′-phase Ni3Al alloys -: art. no. 045104

The optical and magneto-optical properties of two gamma'- phase Ni3Al alloys (Ni0.752Al0.248 and Ni0.771Al0.229) have been investigated experimentally and theoretically. In the optical-conductivity spectra of the investigated alloys two intense interband absorption features at similar to0.8 eV and similar to4.2 eV were experimentally observed. The peak at; 0.8 eV was theoretically predicted, but not experimentally confirmed in the previous investigations. The low-energy peak exhibits a multiple-peak structure for Ni0.771Al0.229 alloy. It is also theoretically shown that the fine structure of the low-energy absorption features originates from the extra spin ordering due to the appearance of the so-called antistructure Ni atoms and their clusters in the Ni0.771Al0.229 alloy, and it is experimentally shown that this fine structure persists up to room temperature. The temperature dependencies of the optical and magneto-optical properties of Ni0.771Al0.229 alloy can be ascribed to the presence of magnetic inhomogeneity in the sample. The existence of magnetic inhomogeneity in the alloy is further confirmed by the ac magnetic- susceptibility measurements in which the susceptibility curve exhibits two magnetic transitions, one at 87.5 K and the other at 252 K. The spin ordering (paramagnetic-to-ferromagnetic transition) and Ni enrichment play a key role for the physical properties.