Exchange interactions in rare earth—transition metal compounds

Using the strenght of R—R interactions deduced from the ordering temperatures of RNi 2 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 mT nB 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 RNi 2 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.