Measurements and Theoretical Calculations of Magnetic XAFS for Ni-Mn Alloys in Ordered and Disordered States

Abstract

We have measured the Mn K-edge magnetic EXAFS and XANES (K-XMCD) of Ni 0.75 Mn 0.25 alloys prepared by various annealing times. The 2nd peaks in the Fourier transform attributed to Mn-Mn pairs in the ordered phase are greatly enhanced in comparison with those in conventional EXAFS. This result suggests that some of Ni atoms in the 2nd shell are replaced by Mn atoms, which have large magnetic moment in comparison with Ni atoms, due to heattreatment induced atomic ordering. Relativistic theoretical calculations well explain the observed magnetic EXAFS and K-XMCD. We estimate that the ratio of the magnetic moments of Mn to that of Ni, which increases as annealing time. It is suggested that the magnetic moment of Mn atom increases with increase of the ordered phase by annealing.