Interpretation of hyperfine fields in concentrated ferromagnetic alloys

The magnetic properties of Heusler alloys of approximate composition Cu2MnAl have been studied by Lorentz microscopy. as a function of composition, heat treatment and plastic deformation. Magnetic domain walls have been observed to be pinned at antiphase boundaries. The strength of pinning varies with composition and heat treatment, being strongest in alloys in which some of the aluminum has been replaced by copper, and in specimens which have been quenched from above the ordering temperature The pinning is thought to be due to antiferromagnetic coupling between the magnetic moments of manganese atoms on opposite sides of antiphase boundaries. Magnetic domain walls are also pinned at antiphase boundaries produced by the splitting of superlattice dislocations during plastic deformation. The results obtained by Lorentz microscopy provide an explanation for the variations of bulk magnetic properties with composition and heat treatment.

Effect of antiphase boundaries on the magnetic properties of Cu-Mn-Al Heusler alloys

Constitution and magnetic properties of Ni-Mn-Sn alloys ― solid and liquid state

Magetic Properties of Cl b -Type Mn Base Compounds

Neutron spin-wave scattering from a Heusler alloy Pd2MnSn

The effective magnetic fields at all non-Mn sites, the nuclear-hyperfine contributions to the specific heat, and the paramagnetic Curie temperatures have been calculated for the Heusler alloys ${\mathrm{Cu}}_{2}$MnAl, ${\mathrm{Cu}}_{2}$MnIn, and ${\mathrm{Cu}}_{2}$MnSn, by an extension of the virtual-bound-state (resonance) model previously used by Caroli and Blandin. The required electronic $\ensuremath{\xi}$ factors are determined from paramagnetic-susceptibility and Knight-shift data on dilute Cu-base binary alloys; and a phenomenological procedure is used to estimate the reduction in $\ensuremath{\xi}$ factors appropriate for the corresponding ions in the Heusler alloys. The latter effect is important, and failure to take the reduced $s$-wave character into account yields hyperfine fields which are too large by a factor of 2-4 for the polyvalent ions. Our predictions for those saturation hyperfine fields which have not yet been determined are -355\ifmmode\pm\else\textpm\fi{}45 KOe for In in ${\mathrm{Cu}}_{2}$MnIn, and -280\ifmmode\pm\else\textpm\fi{}45 and -260\ifmmode\pm\else\textpm\fi{}100 kOe for Cu and Sn, respectively, in ${\mathrm{Cu}}_{2}$MnSn. The nuclear-hyperfine contribution to the specific heat of ${\mathrm{Cu}}_{2}$MnIn is predicted to be $\frac{(5.94\ifmmode\pm\else\textpm\fi{}1.11 \mathrm{mJ}\ifmmode^\circ\else\textdegree\fi{}\mathrm{K}{\mathrm{mole}}^{\ensuremath{-}1})}{{T}^{2}}$. We give a critical and comprehensive comparison of theoretical results and available experimental data.

P. Ganguly

Papers

Hyperfine Fields and Curie Temperatures of the Heusler Alloys Cu 2 MnAl, Cu 2 MnIn, and Cu 2 MnSn