Origin of magnetic anisotropy in R2Fe14B (R=rare earth) compounds: Crystalline electric field model calculations (abstract)

Abstract

The tetragonal R2Fe14B compounds have attracted a great deal of attention because of the permanent magnet applications of the Nd-Fe-B system. Nd2Fe14B shows a spin reorientation from an axial arrangement at 300 K to a conical-type structure below 140 K. In contrast, Pr2Fe14B remains axial down to 4.2 K. We show that this behavior in the Pr and Nd compounds results from an interplay of crystalline electric field (CEF) effects and the R-Fe exchange interaction. There are two inequivalent R sites ( f and g) in these compounds which are magnetically further split into f 1, f 2 and g1,g2 sites. The CEF parameters B02 and B22 for each site are taken from the 155Gd Mössbauer measurements in Gd2Fe14B and the R-Fe exchange field is estimated from the Gd magnetization.1 These parameters are suitably scaled for the rare-earth ion under consideration. It is shown that with the known values of B02, B22, and Hex and with B04 =0.118 K for Nd (which corresponds to B04 =0.35 K for Pr), the four-site calculation, employing these three CEF terms, predicts a spin reorientation in Nd2Fe14B at about 130 K but an axial behavior in Pr2Fe14B at all temperatures.