Tetragonal structure and uniaxial magnetic anisotropy in the arc-melted (Ce,Zr)2(Fe,M)17 (M = Mo, W, Co) alloys

Abstract

The tetragonal ThMn12-type structure is stabilized in (Ce1-xZrx)2T16M (x = 0.2 – 0.3; T = Fe or Fe/Co, M = Mo or W) arc-melted alloys. Approximately 5 at% of Mo or W admixture is sufficient to transform the hexagonal Th2Ni17-type structure of (Ce1-xZrx)2Fe17 into the tetragonal ThMn12-type structure of nearly single-phase (Ce1-xZrx)2Fe16M and/or (Ce1-xZrx)2Fe15CoM bulk alloys. X-ray Rietveld refinements reveal that Zr and Mo (W) substitute different sites in the tetragonal crystal structure. Zirconium preferentially replaces Ce, whereas Mo (W) substitutes Fe. At room temperature, the tetragonal phases exhibit strong ferromagnetism and a uniaxial magneto-crystalline anisotropy with anisotropy fields of 15 – 17 kOe. These materials possess room-temperature saturation magnetizations of 95 – 105 emu/g and Curie temperature of 420 – 505 K. At some concentrations, concurrent Zr and Mo (W) site occupancy facilitates 1:12 structure formation in bulk alloys with minimal presence of non-magnetic element in the Fe sublattice, thus securing the highest known magnetic moment per Fe atom (∼ 1.37 µB) in this type of materials. The intrinsic magnetic characteristics, as well as the absence of critical rare earths (RE), make these compounds interesting for development as low-cost permanent magnets. Small Co additions improve the Curie temperature, especially if combined with W.