A structural study and some magnetic properties of the Hf(Fe,Cr)2 series of intermetallic compounds

We report the synthesis of transition metal based Laves phase compounds HfFe 2- x Cr x (0 ≤ x ≤ 2) and present a systematic study of their structural and magnetic properties by combining X-ray diffraction, scanning electron microscopy, energy dispersive X-ray microanalysis, and magnetization measurements. X-ray powder diffraction analysis reveals that all of the alloys crystallize in the hexagonal MgZn 2 -type structure with the space-group symmetry P6 3 /mmc . It is further shown that Cr for Fe substitution in HfFe 2- x Cr x leads to a highly anisotropic lattice expansion: the initial growth along the six-fold symmetry axis c is more rapid than that in the ab basal plane. The substitution of Cr for Fe induces an increase of the unit-cell volume, by contrast, the intrinsic magnetic properties, spontaneous magnetization M S and Curie temperature T C , exhibit the opposite trend. Indeed, a strong reduction of M S and a huge decrease of T C are observed upon increasing Cr concentration. T C drops from 600 K to 47 K as x changes from 0 to 1. These findings illustrate the strength of the coupling between spin degrees of freedom and crystal lattice in these Laves phase materials.