By using the interatomic pair potential obtained with the lattice inversion method, the stability of RT13-xMx (R = La, Ce, Pr and Nd; T = Co and Fe; M = Si, Al, Cr, V and Ti) of the NaZn13 type and its derivative structure are studied. The structural transition of LaT13-xSix (T = Co and Fe) between the cubic one with the space group Fm3c and the tetragonal one with 14/mcm is imitated from the viewpoint of energy. As for the function of the third elements, Al and Si are beneficial to the phase stability of RT13-xMx, whereas Cr, Ti and V are unfavourable to the stability. In the calculation, the range of x, with which RT13-xMx could crystallize in the cubic or tetragonal structures, agrees with the experiments very well. The calculated crystallographic parameters coincide with the experimental observation. In the cubic structure, Si and Al prefer the 96i site, and in the tetragonal structure Si first occupy the 16l(2) site, then the 16k site. In addition, all the site positions of the compounds with either the cubic or tetragonal structure are really congruent with the experimental one.

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Theoretical study of phase forming of NaZn13-type rare-earth intermetallics

The phase relations of the GdCo13−x Six system have been studied by means of scanning microscopy, microprobe analysis and x-ray diffraction. Single-phase samples GdCo9±δSi4∓δ (structure type LaFe9Si4 with space group I 4/mcm) ar ef ormed in a narrow composition range |δ| 0.2, where GdCo9Si4 forms as af ully ordered ternary compound. The magnetic properties of GdCo9Si4 have been investigated by ac susceptibility, magnetization, specific heat and resistivity measurements. These experiments reveal ferrimagnetism below about 47 K, which is analysed in terms of a two-sublattice molecular field model with a local moment Gd subsystem coupling antiparallel to the itinerant ferromagnetic Co 3d sublattice. The 3d–3d exchange of the latter is the driving force for the onset of long range magnetic order. The validity of the twosublattice model is demonstrated by high field measurements, showing that the ferrimagnetic coupling starts to break up at a lower critical field µ0 Hl � 27 T. The magnetic ground state of GdCo9Si4 has been analysed on a microscopic basis via LSDA electronic structure calculations. (Some figures in this article are in colour only in the electronic version)

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Phase formation and ferrimagnetism of GdCo9Si4

The crystal structure and magnetic properties of LaCo13−x−yFexSiy compounds were investigated by means of x‐ray powder diffraction and magnetization measurements. The substitution of Si for Co induces an order–disorder transition from the cubic NaZn13‐type to its tetragonal derivative structure, while the substitution of Fe for Co does not induce such a phase transition. After annealing treatment, the homogeneous range of the cubic phase is narrowed and that of the tetragonal phase is extended. From crystallographic and thermodynamic points of view, the sta‐ bility of the cubic and the tetragonal phases is discussed. The measured magnetic moment of LaCo13−x−yFexSiy coincides well with the theoretical prediction based on the magnetic valence model. Within the framework of this model, LaCo13−x−yFexSiy compounds can be considered as strong ferromagnets and their magnetic moment can be theoretically predicted. The composition dependence of Curie temperature is discussed within the mean field approximation. At...

Crystal structure and magnetism of LaCo13−x−yFexSiy compounds

New phases in the thorium-iron-tin system: ThFe0.22Sn2 and Th4Fe13Sn5☆

Magnetic behavior of LaCo13−xSix in the vicinity of the critical concentration x=4

mined by means of x-ray powder di6raction In this region there exist four ternary compounds: LaCoSi3, LaCoSi2, LaCoS ie, atomic ordering occurs Magnetic measurements indicate that the tetragonal LaCo» Si intermetallic compounds are ferromagnetic with Curie temperature higher than 900 K and anisotropy fields of about 10 kOe The saturation magnetic moment per Co atom in the tetragonal LaCo» Si„compounds decreases with Si content The composition dependence of the saturation magnetic moment per Co atom can be satisfactorily explained by the rigid-band model

Y. L. Zhang

Papers

Phase relation, crystal structure, and magnetic properties of La-Co-Si alloys