The relationship between magnetic interactions and near neighbor interatomic distances in the transition metal sublattice of R(Mn/Fe)6A6 (R=Nd or Sm, A=Ge or Sn)

Abstract

The magnetic and crystallographic structures of R(Fe/Mn) 6 A 6 ͑RϭNd or Sm and AϭGe or Sn͒ intermetallics have been investigated using x-ray and neutron diffraction techniques and superconducting quantum interference device magnetic measurements. For both stannides ͑AϭSn͒ and germanides ͑AϭGe͒, the lattice contracts with increasing iron content. In the case of the stannides, substitution of manganese by iron enhances the saturation magnetization and Curie temperature at low iron concentrations (xр2) suggesting the presence of an extremely rare occurrence, positive coupling between iron and manganese magnetic moments. In contrast, the magnetic properties of the germanides deteriorate rapidly as manganese is replaced by iron. This difference in the dependence of magnetic properties on the iron content between the germanides and stannides is explained using the Bethe-Slater relationship between near neighbor exchange interactions and interatomic distances. Based on the observations described in this article, it is concluded that the critical near neighbor interatomic distance above which manganese/iron moments couple positively in these intermetallics is ϳ2.614 Å.

High-Pressure Synthesis and Magnetism of the 4H-BaMnO3 Single Crystal and Its 6H-Type Polymorph

“…The symbol of the direct exchange integral is related to the Mn–Mn distance. A shorter Mn–Mn distance is favorable for AFM ordering . CaMnO 3 crystallizes into a GdFeO 3 -type structure with space group Pnma , where the MnO 6 octahedra are all corner-sharing, with the average Mn–O–Mn bond angle being about 157.8° .…”

A Mössbauer spectral study of the NdMn6−xFexGe6 solid solutions

“…Hence, the increase in Curie temperature for a small iron content does not result from a unit-cell expansion, as is usually observed [13] upon nitrogenation or hydrogenation of the R 2 Fe 17 compounds. Even though the presence of ferromagnetism in the RMn 6−x Fe x Ge(Sn) 6 compounds requires a minimum distance [14] between transition metal near neighbours of 2.614Å, there is no direct relationship between the Curie temperature and the distance. As was observed [7] for the NdMn 6−x Fe x Sn 6 solid solutions, the introduction of iron in NdMn 6 Ge 6 adds some electrons to the 3d majority band and, as a consequence, both the Curie temperature and the magnetic moment increase, an increase that is in agreement with observation [4].…”

Thermodynamic assessment of the Ga–Sc and Ga–Tb systems

“…The compounds crystallize in a variety of structures depending on the rare elements and the preparation techniques [1][2][3][4][5]. The physical properties, especially the magnetic properties are sensitive to the constituent elements (R, T and M) and the annealing conditions [6][7][8][9][10]. Moreover, some investigations have shown that the substitution of Ga for the non-magnetic M could make the antiferromagnetic RMn 6 M 6 become ferromagnetic RMnM 6−x Ga x with spontaneous magnetization [11][12][13].…”