X-ray diffraction research of the order–disorder transitions in the ternary heusler alloys B2MnAl (B = Cu, Ni, Co, Pd, Pt)

Abstract

X‐rays diffraction studies of the processes of ordering of atoms in the Heusler alloys B2MnA1 (B = Cu, Ni, Co, Pd, Pt) indicate that these transitions proceed according to the following scheme: i.e. two transitions occure: from the structure L21 to B2 and from the structure B2 to A2. The values of the critical temperatures of the above transitions obtained experimentally are in sufficient agreement with the theoretical results. There is also a agreement between the measured and calculated values of the lattice constants of the investigated alloys.

Full-Potential Screened KKR Calculations for Magnetism of Co<SUB>2</SUB>MnSi, Ni<SUB>2</SUB>MnAl and Ru<SUB>2</SUB>MnSi, Based on the Generalized Gradient Approximation

“…We have also shown that for Ni 2 MnAl, the magnetism changes from FM to AFM at elevated temperatures because the energy gain due to the 2nd neighboring Mn-Mn exchange interaction, which is induced by the atomic disordering of Mn and Al (B2-structure) at elevated temperatures, overcomes the energy loss due to the spin-flip energy of Mn impurity in Ni. This result explains the experimental results 11,12) very well. The possibility of half-metallicity of Co 2 MnZ (Z = Na$S) was examined qualitatively.…”

“…9,10) However, it is also known experimentally that the magnetism of Ni 2 MnAl changes easily from the FM state to antiferromagnetic (AFM) state at elevated temperatures. 11,12) This change of magnetism may be caused by the change of the atomic structure, from the L2 1 structure to the B2-disordererd structure, which occurs at elevated temperatures. 11,12) The fabrication of Ni 2 MnAl at the L2 1 structure seems to be very difficult.…”

“…11,12) This change of magnetism may be caused by the change of the atomic structure, from the L2 1 structure to the B2-disordererd structure, which occurs at elevated temperatures. 11,12) The fabrication of Ni 2 MnAl at the L2 1 structure seems to be very difficult. The electronic structures and magnetism of these full-Heusler alloys may be unstable for the defects and the substitutional disordering.…”

“…Under these circumstances, using the GGA-FPKKR calculations, we planed to study the electronic structures and magnetism of the full-Heusler alloys with and without defects. 11,12) and (presumably weak) AFM of Ru 2 MnSi. 16) We show: (1) the present calculations reproduce the experimental ground states of magnetism, the measured values for the lattice parameters and the available values for the MMs of these alloys, and elucidate the fundamental features of magnetism; (2) the change from the FM to the AFM state of Ni 2 MnAl at elevated temperatures, being known experimentally, is understood by the Mn spin-flip energies and the Mn-Mn exchange interaction energies in X (= Co, Ni), both of which are also calculated in the present work; (3) the Co 2 MnZ (Z = sp-element) at the L2 1 structure shows the half-metallicity if the valence-electron number of Z is between 3 and 5.…”

Combinatorial Investigation of Ferromagnetic Shape-Memory Alloys in the Ni-Mn-Al Ternary System Using a Composition Spread Technique

“…7,27) The screening technique employs micromachined arrays of mechanical cantilever libraries to detect structural transformation in thin-film composition spreads, combined with room-temperature quantitative remnant magnetization mapping using a scanning SQUID microscope. In addition, a scanning x-ray microdiffractometer is used to map the structure.…”