Crystal structures and electron-density distributions of Y(Fe, M)12 (M = Si, Ti, V, Cr, Mo, and W) determined by Rietveld and MEM analyses

Hiroyuki Suzuki

doi:10.1063/1.5135334

Abstract

The crystal structures of Y(Fe, M)12 (where M = Si, Ti, V, Cr, Mo, and W) were investigated by Rietveld analyses, and electron-density distributions were estimated by the maximum entropy method. There were no substituting elements to distort the lattice similarly. While the sites arranged selectively according to the element did not move necessarily, the distance between two atoms in the 8i site (an iron dumbbell) could change freely. Electron-density distributions revealed isolated iron dumbbells and a bonding network between Y, 8f, and 8j sites. Moreover, the connection in an iron dumbbell was much stronger than any other connection. As the substituting amount of the tungsten element increases, the electron density at interstitial positions increases. However, the high electron density disappears by over-substitution. It was suggested that the network of 22-hedrons, which configured the Y, 8f, and 8j sites, correlates with the thermal stability of the ThMn12 structure.

Highlights

Iron-rich rare-earth compounds with a ThMn12 structure (RFe12) are candidates for being used as permanent magnets with high magnetization and large magnetic anisotropy
In (a), while the lattice constant a was enlarged scitation.org/journal/adv by substituting titanium, molybdenum, and tungsten atoms, the lattice constant a was almost unchanged by substituting vanadium and chromium atoms, and the lattice constant a was shrunk by substituting silicon atoms
Lattice structures of Y(Fe, M)12 were investigated by Rietveld analysis systematically, and electron-density distributions were estimated by the maximum entropy method (MEM)

Summary

Introduction

Iron-rich rare-earth compounds with a ThMn12 structure (RFe12) are candidates for being used as permanent magnets with high magnetization and large magnetic anisotropy. RFe12 cannot form equilibriumly without stabilizing elements (M) such as silicon (Si), titanium (Ti), vanadium (V), chromium (Cr), molybdenum (Mo), and tungsten (W). In (c), the distances between the 8i sites (except for substitutable silicon and tungsten atoms) change largely despite the difference in the preferable sites of each element, indicating that the distance between the 8i sites (the distance between two atoms in an iron dumbbell) is independent of structural stability and change freely.

Results

Conclusion