INVESTIGATION OF MIXED INTERMETALLIC COMPOUNDS

Abstract

The results of Mossbauer measurements on the intermetallic compounds (Fei-,Coz)2B (O < x -c l), (F~I-,CO,)B (O < x < 0.5) and (Fei-,MnX)Bez (O < x < 1) are presented. The electron density (i. e. the isomer shift) at the iron sites remains unchanged for alloy- ing in each of these systems. The hyperfine field values suggest a nearly constant iron moment in (Fe~-~co,)iB and (F~I-~CO,)B, whereas it decreases in (Fei-,Mn,)Bez. The comparison with the average magnetization for the (Fe 1 -,Coz)~B and (Fe 1-,Mn,)Bez compounds suggests an important decrease in the magnetic moments of Co and Mn atoms, respectively. The considerable similarity in the magnetic moment versus electron concentration curve of the isomorph series of T2B and TB compounds (T = 3d transition element) to the Slater-Pauling curve of the same transition-metal alloys led to the assumption (l) that the valence electrons of the metalloid transfer to the d-band of the metals (the so-called donor model). This electron transfer causes a shift of the Slater-Pauling curve as a whole to the lower electron concentration by about 1.5 electrons for each added boron atom. The low temperature specific heat measurements (2) supported this idea and the model was extended (3) for ternary alloys formed from FeBe, by substitution of other 3d metals. There is a correlation in these binary compounds between the magnetic moment and isomer shift at iron sites in agreement with the expectation that the metalloid fills the d-band of the metal (Fig. 1). The increase in the isomer shift corresponds either to a decrease in the 4s- or to and increase in the 3d-electron density. The main contribution to the iron hyperfine field for these compounds is the core polarization contribution (i. e. proportional to their own magnetic moment), thus the latter case is preferred, i. e. the iron 4s-electron density at the Fermi surface is thought to be very small (7). These experimental data support the