Hyperfine field at 111 Cd nuclei in Heusler Alloys

The magnitudes and signs of the hyperfine fields in the ordered ferromagnetic Heusler Alloys X2MnZ and XMnZ (where X is Cu, Ni, Pd while Z is In, Sn and Sb) have been investigated at liquid nitrogen and room temperatures using TDPAC method. Their signs have been found to be negative. The results have been compared with the predictions of Caroli-Blandin and Campbell-Blandin models and RKKY theory. I. Introduction The investigated ferromagnetic Heusler Alloys containing Mn atoms were magnetically and chemically ordered with L21 structure, having the typical composition X2MnZ , or with the CI b structure in the composition XMnZ [i]. Various magnetic studies have suggested that the magnetic moments of about 4 ~B are confined only to the Mn atoms. The hyperfine fields at nonmagnetic element sites in Heusler Alloys are especially interested in the relation to (i) the conduction electron spin polarisation, which originates from the Mn magnetic moment and (ii) effective exchange interactions between the magnetic atoms. The hyperfine fields on sp elements at Z sites in such alloys have been extensively investigated in many work. The exception is the cadmium element for which it is not possible to use the M~ssbauer effect and NMR methods in the hyperfine field studies. Therefore, in the present work the TDPAC method was applied. 2. Experimental Procedure In all Heusler Alloy samples investigated in the present work 1.5 at % of the Z site atoms were replaced by indium atoms containing radioactive lllln which decays to lllcd. The appropriate quantities of spectrographically pure elements were pulverized, mixed together, pressed into the form of a pellet and melted in an alumina crucible in argon atmosphere, and then allowed to cool from the molten state to the room temperature. The ingots were pulverized again, mixed and pressed, and then annealed in an appropriate temperature in argon atmosphere for 2-3 days. After annealing the specimens were either quenched into iced water or slowly cooled down.