SINGLE-ION RARE-EARTH ANISOTROPY IN THMN12-TYPE COMPOUNDS

The single-ion rare earth anisotropy was investigated in ThMn12-type c ompounds. For this purpose the crystal electric field parameter values were studied. In these compounds, described by formula RFe12-xTx, R = rare earth, T = Ti, V, Cr, Mo, W and Si, the T atoms have strong crys tallographic site preference changing the local crystal electric field potential which ''sees'' the rare earth ion. The crystal electric fie ld potentials A2(0) were calculated considering this site preference. The summations were performed taking into account the nearest neighbor hood of the rare earth ion according to the recent results of band str ucture calculations. The charges of the surrounding Fe and T atoms wer e established applying the chemical bond model proposed by Pauling. Th e absolute value of A2(0) decreases when the content of vanadium incre ases in 8(i) position, which is in agreement with experimental data. L ocalization of Si atoms in 8(i) and 8(f) causes a decrease in A2(0). T he Gd-155 Mossbauer spectroscopy data confirm this fact. Miedema's ''m acroscopic'' atom model of cohesion in alloys was applied for interpre tation of the role of T atoms in the isomer shift and volume effects.