Evidence of Clustering in Heusler like Ferromagnetic Alloys

Abstract

Two Heusler like alloys Fe 2 CrAl, and Mn 2 CoSn had been prepared and studied using the Mössbauer effect. Both these alloys were ferromagnetic in nature. Their Mössbauer spectra showed the co-existence of a paramagnetic portion along with magnetic hyperfine part upto temperatures well below their Curie temperatures. Low temperature Mössbauer spectra for both these alloys showed a steady variation in the intensity of the paramagnetic portion. X-ray diffraction studies made on these samples ruled out the possibilities of a separate phase. Explanation of the observed phenomena is given by clustering around the magnetic ions present in these samples.Recently there has been a lot of interest in Heusler alloys because theoretical band structure calculations [1] predict that some of the Heusler alloys are halfmetallic ferromagnets. Although Groot et al.[2] had predicted the Heusler alloys NiMnSb and PtMnSb to be half-metallic as early as 1983; this property has given rise to a new surge of interest in these systems due to the possibility of use of Heusler alloys as material for spin electronic devices. These systems are attractive because of the considerable change in their magnetic properties that can be made by altering the chemical ordering, substituting for one or more components by other atoms, mechanical treatment etc.Ternary alloys of stoichiometric composition bearing the general formula X 2 YZ are called Heusler alloys. In this class of alloys, X and Y are generally transition elements and Z an sp element. These alloys offer excellent systems for studying magnetic interactions. Many of these alloys can be held at various degrees of order leading to a corresponding change in their magnetic properties.

Magnetic anisotropy induced by high energy ball milling of Fe2MnAl

“…The contribution to the paramagnetic singlet from superparamagnetic particles is therefore negligible and originates almost entirely from the presence of Mn clusters as observed in studies of Fe 2 Cr ͑1−x͒ Mn x Al and Mn 2 CoSn. 14,15 Mössbauer studies show that nearly 12% Fe is in these clusters. The high temperature Mössbauer spectrum ͓Figs.…”

Exchange interactions and Curie temperatures of Mn2CoZ compounds

“…Recently, the Mn 2 YZ compounds with Hg 2 CuTi structure have attracted considerable theoretical and experimental activities, where Y = Fe, Co, Ni, Cu [1][2][3][4][5][6][7][8][9][10]. Some of these compounds have been characterized as half-metallic ferrimagnets.…”

Electronic, magnetic, and structural properties of the ferrimagnet Mn2CoSn

“…Experiments on Mn 2 CoSn were previously reported by different groups [24][25][26][27]. According to Ref.…”