Ferromagnetism in ZrFe12−xAlx and HfFe12−xAlx (x = 6.0, 6.5, 7.0)

Abstract

Results of crystal structure, microstructure, and magnetic properties studies of arcmelted and annealed ZrFe6Al6, ZrFe5.5Al6.5, ZrFe5Al7, HfFe6Al6, HfFe5.5Al6.5, and HfFe5Al7 are reported. These compounds adopt the ThMn12 structure-type (space group 139, I4/mmm), like their more common rare-earth analogues. Analysis of powder x-ray diffraction data show that the 8f site is occupied by Fe, the 8i site by Al, and the 8j site by a mixture of Fe and Al. All of the compounds undergo a ferromagnetic transition at temperatures ranging from 170 to 270 K. Three effects on the magnetic properties are noted as the Fe content is increased: decrease in the Curie temperature, decrease in the magnetic moment per Fe at high fields, and the development of non-monotonic temperature dependence of the low-field magnetization below the Curie temperature. First principles calculations indicate a ferromagnetic ground state, but find antiferromagnetic interactions among Fe moments on 8j sites which is likely important in understanding the observed behavior.