Magnetic and Crystallographic Structure of Y₆Mn₂₃D₂₃

The magnetic behavior of Y6Mn23 is dramatically altered upon hydrogenation (or deuteration). In this study it has been found, by means of high-resolution powder diffraction and Rietveld refinement techniques, that the crystallographic structure is distorted from face-centered cubic (Fm3m) at 295 K to a primitive tetragonal structure at 4 K in which deuterium atoms are atomically ordered. Y6Mn23 is a ferromagnetic compound with Tc=486 K, and bulk magnetization of 13.2 Bf.u. (formula unit). After deuteration of Y6Mn23 to the composition Y6Mn23D23, low-temperature scattering data (T\u3c180 K) show that the b and f2 sites in the Fm3m structure are antiferromagnetic and the d and f1 sites have no spontaneous magnetic moment. © 1984 The American Physical Society

A Review of the Magnetic Structures and Properties of the R₆M₂₃ Compounds and Their Hydrides

A review of the magnetic structures and properties of the R6M23 (R ≡ rare earth; M ≡ 3d transition metal) binary compounds, pseudobinary compounds and hydride systems is presented. © 1983

A Powder Neutron Diffraction Study of the LaNi₄.₅Al0.₅D₄.₅ Structure at 298 and 77 °K

Recently, there has been some controversy over the structure of hydrides of the La(Ni//5// minus //xAl//x)//5 system. Once of the proposed structures belongs to the P6/mmm space group and contains five deuterium sites. The other proposed structure belongs to the P31 m space group and contains two deuterium sites. In an attempt to resolve this conflict, a powder neutron diffraction investigation has been carried out for LaNi//4//. //5Al//0//. //5D//4//. //5 at 298 and 77 degree K. A modified Rietveld profile analysis technique was used to interpret the data. It is found that a two-site model using P6/mmm symmetry adequately describes the structure at 298 degree K. At 77 degree K, there is no evidence of magnetic ordering and the structure shows only slight changes from that given at 298 degree K. The lattice parameter a contracts from 5. 341 to 5. 331 A, while c remains constant at 4. 236 A

The Effect of Stoichiometric Variations on the Magnetic Structure of Y₆Mn₂₃

As a consequence of large variations in previously reported magnetic moments of manganese on the four non-equivalent crystallographic sites of Y6Mn23, it was suggested that stoichiometric variations in composition might be responsible. Accordingly, non-stoichiometric ingots of Y6Mn23 were prepared ranging in composition (precast analysis) from Y6Mn21 to Y6Mn26. On the basis of atomic absorption analysis, high precision back-reflection X-ray diffraction and Rietveld profiling of powder neutron diffraction data, we conclude that extreme variations in stoichiometry cause little change in the magnetic moment magnitudes and that the variable results reported probably arise from the presence of small amounts of a second phase, YMn2 in the manganese-deficient samples and YMn12 in the manganese-rich samples. © 1983