Soft‐x‐ray appearance potential spectroscopy study of Pr₂Fe_14−xCo_xB

The praseodymium–iron–boron alloy, Pr₂Fe₁₄B, is found to possess excellent permanent‐magnet properties. In this paper we report the investigation of the electronic structure of the system Pr₂Fe_14−x Co_x B (x=0, 3, 5, 7, and 8.5) by soft x‐ray appearance potential spectroscopy (SXAPS). SXAPS exploits the abrupt changes in the total x‐ray emission associated with the thresholds for the excitations of core levels of the atoms in the surface region of the materials. This technique is particularly suitable for investigating the changes in the unoccupied states of rare‐earth and transition‐metal intermetallics which have high density of empty states at the Fermi level.The Pr M₅ ‐level SXAPS peak in the system is found to exhibit negative chemical shift which progressively decreases as a function of Co concentration. However, the L_2,3 levels of Fe and Co show increasing positive chemical shift. The chemical shifts data display a maximum at x=7 in these three cases which correlates well with reported behavior in the lattice constants of alloy systems. These chemical shifts have been discussed on the basis of charge transfer among the constituents of the system. The full width at half‐maximum of the L₃ peaks of Fe and Co indicates a decreasing trend as a function of Co concentration. These spectral characteristics have been interpreted in terms of the d‐band narrowing as a result of interaction between 3d bands of Fe and Co.