Magnetic properties of RFe11.3W0.7 (R = Dy, Ho, Er, and Lu): On the R-Fe exchange interaction in the R(Fe, T)12 class of compounds

Results of x-ray powder diffraction and magnetic measurements performed on RFe 1 1 . 3 W 0 . 7 compounds, where R=Dy, Ho, Er, and Lu, are presented. The Curie temperature, saturation magnetization, and spin reorientation transitions are discussed in relation to several RFe 1 2 - x T x systems, where T=Ta, Nb. Mo, Ti, and the x-substituent concentration is within a narrow range x = 0.5-1.0. In these systems, the dependence of the Curie temperature versus the unit cell volume, for a given R partner, suggests combined size and electronic effects produced by the T atom. The strengths of the rare-earth-iron and iron-iron exchange interactions are evaluated in the mean-field framework, and analyzed with reference to RFe 1 2 - x T x compounds, with T=Ta, Re, Nb, Mo, Ti, Cr, and V. Based on (i) the phenomenological mean-field model accounting for the sublattice of conduction band electrons, (ii) Brooks' reinterpretation of Campbell's formulation of the intersublattice exchange, and (iii) Wigner-Seitz cell analysis, we explore the role played by the conduction band electrons, particularly the nd-type electrons (n=3, 4, 5), on the intersublattice exchange coupling in the iron-rich RFe 1 2 - x T x class of compounds. It is proposed that the variation in the conduction-electron density, by varying the T element type and concentration, leads to a modification of the 5 d band occupancy number and consequently, of the R-Fe intersublattice exchange coupling.