Magnetic structures and magnetic phase transitions in RMn2Si2

Magnetic properties of the LaMn2Si2 and La0.6R0.4Mn2Si2 (R = Sm, Tb, Gd) compounds with layered ThCr2Si2-type structure have been studied using quasi-single-crystalline and polycrystalline samples. Substitution of the R atoms for La decreases the interatomic distances and changes the ordering of the Mn sublattice from ferromagnetic to antiferromagnetic. Magnetic structure of the substituted compounds has been found to depend on the anisotropy of R ions. The Sm moments are oriented in the basal plane and weakly coupled with the Mn sublattice. For R = Tb, frustrations prevent the formation of long-range magnetic ordering in Tb sublattice. For the system with Gd, the antiferromagnetic Mn-Mn and Gd-Mn interactions lead to a change of magnetic anisotropy from the easy-axis to the easy-plane type.