Magnetic study of the compounds RMn(2)Ge(2) (R equivalent to La-Sm, Gd) and R(x)Y(1-x)Mn(2)Ge(2) (R equivalent to La, Lu; 0<x<1) above room temperature

The Neel temperatures of the compounds RMn(2)Ge(2) (R = La, Pr, Nd, Sm, Gd0.5Sm0.5) were determined by susceptibility measurements above the Curie point (T-N = 413, 414, 418, 389 and 374 K respectively). A similar study of the R(x)Y(1-x)Mn(2)Ge(2) (R = La, Lu; 0 < x < 1) solid solutions within the temperature range 300-800 K enables the Neel points T-N, paramagnetic Curie temperatures theta(p), Curie constants C and temperature- independent paramagnetism chi(o) to be measured. The variation of the above parameters was studied as a function of the in-plane Mn-Mn spacings. The results show a discontinuity for C and chi(o) in the proximity of d(Mn-Mn) = 2.85 Angstrom. The temperatures T-N and theta(p), however, exhibit a more continuous variation. Therefore T-N and theta(p) further permit the evaluation of the evolution of intralayer and interlayer coupling as a function of the Mn-Mn contacts. An increase in this distance is followed by an increase in the antiferromagnetic character of the Mn(001) planes and a decrease in the antiferromagnetic character of the interlayer coupling.