Spin Waves in Heusler Alloys Pd2MnSn and Ni2MnSn

Abstract

The magnetic interactions in Heusler alloys Pd 2 MnSn and Ni 2 MnSn have been investigated using neutron spin wave scattering. The spin wave dispersion relations along the [00ζ], [ζζ0] and [ζζζ] directions have been observed across the whole magnetic Brillouin zone. The results have been analyzed using a Heisenberg Hamiltonian where only Mn atoms have a localized moment. It has been found that the interactions between more than 6th neighbors should be taken into account to reproduce the observation. The exchange constants at large distances have an oscillatory character which can be interpreted by the s - d type interactions based on the nearly free electron model. However, the n . n . and n . n . n . interactions have signs opposite to those expected from the simple s - d model. The n . n . and n . n . n . exchange constants in Ni 2 MnSn ( T C =344 K) are larger than those in Pd 2 MnSn ( T C =189 K), although the oscillatory parts have nearly the same values for both alloys.