Transitions from ferrimagnetism to spin glass behaviour in YFe_xAl_12-x(4≤x≤6)

Magnetization and ⁵⁷Fe Mössbauer studies of YFe_xAl_12-x(x = 4.0, 4.5, 5.0, 5.5, 6.0) of ThMn₁₂ structure at temperatures 4.1 to 350 K have been performed. While YFe₄Al₈ and YFe₆Al₆ order antiferromagnetically and ferrimagnetically, respectively, the samples with x = 4.5, 5.0, 5.5 order magnetically at T_c(105, 160, 225 K) and transform to spin glasses at T_G(84, 82, 128 K). T_G follows, the external field to the 2/3 power, law. The nature of magnetic order is determined by the relative iron occupation of the three crystallographic inequivalent sites, (f), (j) and (i).