Martensitic Transformation and Magnetic Structures Between the Sm-Type and the HCP Structures in Tb-Light Rare Earth Alloys

Abstract

An interesting sequence of close packed structures such as hcp→Sm-type→double hcp→fcc, occurs in the heavy and the light intra-rare earth binary alloys with increasing the composition of lighter elements(1,2). Some alloys located at the boundary of two crystal phases in the intra-rare earth phase diagram, exhibit a temperature induced martensitic transformation between the two close packed structures (3,4). In the previous paper (4), we have reported the preliminary neutron diffraction studies of crystal and magnetic structures of Tb_0.8-La_0.2, Tb_0.8-Pr_0.2 and Tb_0.75-Nd_0.25 using single crystals. Below 30 K, such a martensitic transformation from the Sm-type to the hcp structure was observed for the latter two crystals. The Sm-type crystals order in a sinusoidal magnetic structure (o++o−−o++..) along the c-axis and zeroes correspond to the cubic site, while the hcp crystals have ferromagnetic structure. In the present paper, neutron diffraction studies on Tb_0.803-Pr_0.197 and Tb_0.798-Pr_0.202 single crystals were carried out extensively in both phases of Sm-type and hcp structures at the various stages of cooling and heating cycles that were accompanied by the martensitic transformations between the two phases. The martensitic crystals of hcp and Sm-type structures have stacking faults that increase with increasing number of martensitic cycles.