Abstract :
Analysis of available experimental data leads to the conclusion that the leading crystal field coefficient A20 is negative in the RFe12−xMx compounds, whereas it is positive in RCo12−xMx (R=rare earth, M=V, Ti, Mo). This conclusion is confirmed by density functional electronic structure calculations. The slightly different charge distributions around the Fe and Co atoms situated on the 8j sites neighbouring on the rare earth are shown to be chiefly responsible for the difference in the sign of A20.
