Spontaneous magnetic phase transition and magnetoelastic anomalies at transitions in intermetallic compounds RMn2Ge2 (R = La,Pr,Nd,Sm,Gd,Tb,Y)

The temperature dependence of lattice constants a and c of intermetallic co mpounds RMn2Ge2(R = La,Pr,Nd,Sm, Gd,Tb and Y)is measured in the temperature range 10-800 K using the X-ray method. The magnetoelastic anomalies of a(T ) and c(T) are found at different spontaneous magnetic phase transitions. I t is shown that the magnetoelastic anomalies are mainly determined by the M n-subsystem. Mn-Mn exchange interactions depend not only on the lattice con stant a but also on constant c. Low-temperature ferromagnetic-antiferromagn etic transitions are discussed in the framework of Kittle's exchange invers ion model.