Effect of Co and Zr content on the magnetic properties of SmFe11Ti-based alloys produced by hydrogenation-disproportionation-desorption-recombination

Abstract

The recent increasing demand for magnetic materials for applications such as electric motors in electric vehicles, as well as issues with restrictions to the supply of certain rare-earth elements, has led to renewed interest in SmFe-based alloys. The SmFe12-type crystal structure is especially desirable due to its high saturation magnetisation, but it is difficult to obtain this metastable phase on its own. Co, Zr, and Ti substitutions have been found to improve the magnetic properties and stabilise the hard magnetic Sm1Fe11Ti1 phase, while melt spinning and the hydrogenation disproportionation desorption recombination (HDDR) process have been found to produce fine grain size, and thus high coercivity. Therefore, in this work the effect of Co and Zr content on the magnetic properties of melt-spun and HDDR processed (Sm1-xZrx)(Fe1-yCoy)11.2Ti0.8 samples has been examined, where 0 ⩽ x ⩽ 0.3 and 0 ⩽ y ⩽ 0.25. Melt-spun, HD, and DR samples were analysed to determine the effect of varying the Co or Zr content. Amorphous Sm1Fe11Ti1 phase was found in all melt-spun samples. Co was found to exist in equal amounts in the α-(Fe, Co) and (Fe, Co)2(Ti, Zr) phases in the HD treated samples, while Zr existed mostly within the (Fe, Co)2(Ti, Zr) phase. The crystal size of the α-Fe or α-(Fe, Co) phase was shown to increase with increasing Co content but decreased with increasing Zr content. Increasing Co content generally improved Mr and Ms in the DR treated samples, whereas increasing Zr content was generally detrimental to Mr, Ms, and Hcj. However, each sample had a different fraction of the Sm1Fe11Ti1 phase, and higher Sm1Fe11Ti1 phase fractions were found to increase the Mr, Ms, and Hcj. Values of Mr, Ms, and Hcj corrected for the fraction of Sm1Fe11Ti1 phase were highest in the (Sm0.8Zr0.2)(Fe0.8Co0.2)11.2Ti0.8 sample. This composition should be investigated further to determine if superior magnetic properties can be produced, by optimising the DR treatment conditions to obtain 100 % Sm1Fe11Ti1 phase.