Magnetic X-ray absorption fine structure for Ni–Mn alloys

Abstract

Magnetic X-ray absorption ®ne-structure (XAFS) spectra have been measured for Ni±Mn alloys. The magnetic XAFS in the near-edge region (X-ray absorption near-edge structure, XANES) and X-ray magnetic circular dichroism (XMCD) of the Mn and Ni K-edge for Ni 1Àx Mn x (x = 0.25, 0.24 and 0.20) show that (i) the local magnetic structure around the Mn atom is quite different from that around the Ni atom, and (ii) the peak intensity in the magnetic XANES of the Mn K-edge depends on the magnetization of the sample in contrast to the Ni K-edge. The Mn K-edge magnetic EXAFS (extended XAFS) for Ni 0.76 Mn 0.24 is also measured. The second and fourth peaks in the Fourier transform are observed to be enhanced in comparison with the non-magnetic EXAFS, indicating that the second-and fourthshell Ni atoms are replaced by Mn atoms due to heat treatment (atomic ordering). Semi-relativistic theoretical calculation explains the observed magnetic EXAFS.

Local magnetic structures of Ni–Mn alloys in ordered and disordered states studied by magnetic XAFS

“…To calculate the phase shift for the magnetic EXAFS, we refer to the electronic structures obtained from FLAPW method [4]. The amplitude of the Fourier transform depends on the annealing time for all peaks.…”

“…On the other hand, magnetic XAFS is a powerful technique for the investigations of local magnetic structure such as alloys that undergo order-disorder structural transition. Miyanaga et al [4,5] presented Mn K-edge XMCD results for Ni 1Àx Mn x (x ¼ 0.2, 0.24 and 0.25) [4] and the magnetic EXAFS for Ni 3 Mn. But the change of local magnetic structure with the atomic ordering is still unclear.…”

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

“…shows the comparison between the measured K-XMCD (Exp.III, 500h) and the calculated one. The magnetic moments of Mn and Ni are referred in the literature[4]. The agreement is satisfactory.…”

“…We perform relativistic theoretical calculation [7] of the magnetic EXAFS for binary alloy as the ordered model of Ni 3 Mn including up to 4th shell atoms. To calculate the phase shifts for the magnetic EXAFS, we refer to the electronic structures obtained from FLAPW method [4 ].…”

Local Structure and Dynamics of Functional Materials Studied by X-ray Absorption Fine Structure

“…Ni 3 Mn magnetic alloys have also been a long-studied system, where they have a coupling between the structure disorder and magnetic properties. I studied the magnetic EXAFS for Mn using circular polarized X-ray, and the following is the discussion of the effect of atomic arrangement in order-disorder couplings to magnetic properties [18,19]. In the magnetic EXAFS, the amplitude is proportional not only to the coordination number but also to the magnetic moment of X-ray absorbing and photoelectron scattering atoms because of spin-orbit coupling.…”