Hyperfine Magnetic Fields in Cobalt-Based Heusler Alloys.

Measurement of hyperfine interactions at Cd-111 and Sn-119 impurity nuclei in Co-based Heusler alloys Co _ 2YZ (Y = Mn, Ti, V, Zr and Z was Al, Ga, Ge, Si, Sn) have been made within a temperature range 77K and 746K using the time differential Perturbed Angular Correlation (TDPAC) and Mossbauer techniques. The hyperfine field results in these alloys are discussed in terms of two models, the localized moment model and the Volume Overlap model. In the localized moment model a preasymptotic phase factor eta = pi at distance r = a/2 has been used to fit our experimental results on Co_ 2YZ (Y = Ti, V, Zr and Z = Al, Ga, Sn, Ge). In the Volume Overlap model the hyperfine field results in the series Co_ 2MnZ (Z = Ge, Si, Sn) has been plotted against the lattice parameter of these alloys; a linear relationship has been found out suggesting a non -overlap term between the magnetic atom and the non-magnetic impurity. A prediction of hyperfine magnetic field less than 40 (Koe) on Sn-119 and of about -250 (Koe) on Cd-111 in Co_ 2TiSi and Co_ 2TiGe has been made. Temperature variation of the hyperfine magnetic field in the alloy Co_ 2MnSn with magnetic moments residing on two sites, has been studied. Results didn't show a dramatic deviation from the Brillouin function.