Competing magnetic interactions in rare-earth manganese silicides and germanides

We have investigated the magnetic properties of RxR1-x′Mn2X2 (X: Si, Ge) for various combinations of rare-earth elements R and R′R′ by examining the evolution of the features in the temperature dependence of the low-field magnetization. By making use of the known magnetic structure of the parent compositions x=0x=0 and 1, the results of low-field magnetization measurements are interpreted for intermediate compositions to give information on their magnetic structure. We find antiferromagnetic–ferromagnetic (AF–FM) transitions, whereby the transition can be sharp or evolve over a considerable temperature range. We examine the magnetic transition temperatures as a function of the tetragonal unit cell parameter aa and find that the critical spacings associated with interlayer AF–FM transitions are different in the silicides and germanides.