Single-Ion Rare Earth Anisotropy in ThMn₁₂-Type Compounds

Abstract

The single-ion rare earth anisotropy was investigated in ThMni2-type compounds. For this purpose the crystal electric field parameter values were studied. In these compounds, described by formula RFe 12_xTx , R = rare earth, T = Ti, V, Cr, Mo, W and Si, the T atoms have strong crystallographic site preference changing the local crystal electric field potential which "sees" the rare earth ion. The crystal electric field potentials A20 were calculated considering this site preference. The summations were performed taking into account the nearest neighborhood of the rare earth ion according to the recent results of band structure calculations. The charges of the surrounding Fe and T atoms were established applying the chemical bond model proposed by Pauling. The absolute value of A3 decreases when the content of vanadium increases in 8(i) position, which is in agreement with experimental data. Localization of Si atoms in 8(j) and 8(f) causes a decrease in A 20. The 1 55 GdMössbauer spectroscopy data confirm this fact. Miedema's "macroscopic" atom model of cohesion in alloys was applied for interpretation of the role of T atoms in the isomer shift and volume effects.