Gigantic increase in the Curie temperature of the R(Co1-xMnx)2 (R: heavy rare earths) systems at small Mn concentrations

Abstract Magnetic measurements on the R(Co 1- x Mn x ) 2 Laves phase systems with R = Gd, Tb, Dy, Ho, Er, Tm have been performed. A strengthening of the RCo 2 ferrimagnetism shows up through a rapid increase at small Mn concentration x of the Curie temperature which reaches a maximum for x around 0.25. The results are interpreted by invoking the sole peculiarities of the d-magnetism keeping the R-R and R-d exchange integrals invariable on x .