EXCHANGE INTERACTIONS IN RARE-EARTH TRANSITION-METAL COMPOUNDS

Using the strength of R-R interactions deduced from the ordering temperatures of RNi2 compounds, the R-T exchange-coupling parameter (A(RT)) in R(m)T(n) (R = rare earth, T = Co or Fe, m/n = 1/2; 1/3; 6/23; 1/5; 2/17; 1/12)and R(m)T(n)B(k) (m/n/k = 1/4/1; 2/14/1; 1/12/6) systems has been evaluated from analyses of Curie temperatures. Whereas A(RR), as deduced from the RNi2 compounds, increases by almost an order of magnitude in a given series, A(RT) is enhanced by a factor of only about three from the heavy to the light rare earth compounds. These phenomena, already reported in literature, are based on 4f-5d exchange interactions at R sites. In addition, for a given rare earth element, going from T-poor to T-rich compounds, a tendency to decrease is found for both A(RCo) and A(RFe); this variation is discussed in terms of 3d-5d hybridization.