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-LESS-THAN-X-LESS-THAN-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 simi lar study of the R(x)Y(1-x)Mn(2)Ge(2) (R = La, Lu; 0 < x < 1) solid so lutions 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 vari ation of the above parameters was studied as a function of the in-plan e 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 t heta(p), however, exhibit a more continuous variation. Therefore T-N a nd theta(p) further permit the evaluation of the evolution of intralay er and interlayer coupling as a function of the Mn-Mn contacts. An inc rease in this distance is followed by an increase in the antiferromagn etic character of the Mn(001) planes and a decrease in the antiferroma gnetic character of the interlayer coupling.