A structural study and some magnetic properties of Hf1-Mo Fe2 Laves phase materials

The effects of molybdenum substitution on the structural and magnetic properties of the Hf 1- x Mo x Fe 2 (0 ≤ x ≤ 0.25) transition metal based Laves phase materials have been studied by means of x-ray powder diffraction, scanning electron microscopy, energy dispersive x-ray microanalysis, and magnetization measurements. All of the intermetallic compounds form in the hexagonal MgZn 2 -type crystal structure (space-group symmetry P6 3 /mmc ) and exhibit ferromagnetic ground state. For the x = 0.1–0.25 alloys, microstructural analysis and diffraction data reveal that there are two hexagonal phases with different chemical compositions sharing the same P 6 3 /mmc lattice symmetry but having slightly different unit-cell parameters. This phenomenon in turn is rooted in partial segregation of hafnium and molybdenum, and a peculiar microstructure. Mo for Hf substitution in Hf 1- x Mo x Fe 2 induces an anisotropic shrinkage of the hexagonal cell: the initial contraction in the ab basal plane is more rapid than that along the high-symmetry direction c . It is further shown that the intrinsic magnetic properties, Curie temperature T C and spontaneous magnetization M S , are extremely sensitive to Mo content: a strong decrease of T C and a significant reduction of M S are observed. The ferromagnetic ordering temperature changes from 600 K for x = 0 to 178 K for x = 0.25. • Hexagonal P6 3 /mmc crystal symmetry retained along the series. • Composition dependence of the unit-cell parameters. • Anisotropic shrinkage of the hexagonal cell. • Overall volume contraction of Δ V / V = -7.2 %. • Evolution of T C and M S upon Mo for Hf substitution.