M. Artigas

Gold(I) complexes with the ligand 1-thiolate-1,2-dicarba-closo-dodecaborate. Crystal structure of [Au2(1-S-1,2-C2B10H11)2(μ-dppe)]

Neutral and anionic gold(I) mononuclear derivatives with the 1-thiolate-1,2-dicarba- closo -dodecaborate ligand of stoichiometries [Au(1-S-1,2-C 2 B 10 H 11 )L] and [Au(1-S-1,2-C 2 B 10 H 11 ) 2 ] − have been synthesised. The complex [Au(1-S-1,2-C 2 B 10 H 11 )(AsPh 3 )] is a good starting material for the synthesis of the dinuclear gold(I) derivative [Au 2 (1-S-1,2-C 2 B 10 H 11 ) 2 ( μ -PP)], where PP is a diphosphine. The compound [Au 2 (1-S-1,2-C 2 B 10 H 11 )(PPh 3 ) 2 ]BF 4 has also been prepared. The structure of the neutral complex [Au 2 (1-S-1,2-C 2 B 10 H 11 ) 2 ( μ -dppe)] is confirmed by single-crystal X-ray diffraction. There are no short gold–gold interactions.

Structural, magnetic and hydrogenation properties of R2Fe17−xSix compounds (R=rare earth element): II. Effects of hydrogen insertion on the magnetic properties (R=Ce, Nd; 0≤x≤5)

Abstract Substitution of silicon for iron in R 2 Fe 17 compounds yields a decrease of the cell volume, conversely a huge increase of the Curie temperature is observed up to x ≈3. The hydrogenation properties of the R 2 Fe 17− x Si x compounds with R=Ce, Nd, show a marked reduction of the maximum hydrogen uptake related directly to the Si substitution rate. Magnetisation analysis allows to correlate the cell parameter expansion of the Ce 2 Fe 17− x Si x series to the interstitial site occupation.

Comparison of the magnetic properties of ErMn12 − xFex series with their related hydrides and carbides

Abstract The magnetic properties of ErMn12 − xFex (0 ⩽ x ⩽ 8) and their related hydrides and carbides have been studied by magnetisation measurements and neutron diffraction. Modifications in the magnetic correlations are found depending on the nature of both the 3d metal and the inserted element.

Relationship between the structural and the magnetic properties of ErMN12 − xFex compounds

Abstract The crystal and magnetic properties of intermetallic compounds of formula ErMn12−xFex with x = 0, 2, 4, 6, 8, have been analyzed versus the relative distribution of the transition metal (Mn or Fe) on the different d-metal sites of the tetragonal structure. Neutron diffraction and magnetisation measurements allow better understanding of the relationships between the atom ordering and the (Mn,Fe)-(Mn,Fe), (Mn,Fe)-Er and Er-Er magnetic couplings.

Heat capacity of RFexMn12−x (R = Gd, Tb and Dy) compounds: wiping out a cooperative 4f–4f exchange interaction by breaking the 3d–4f magnetic symmetry

Using adiabatic calorimetry the heat capacity of a series of RFex Mn12−x (R = Gd, Tb and Dy) compounds has been measured from 3 to 350 K. The substitution of Fe for Mn in RFex Mn12−x influences both the magnetic interactions on the 3d sublattice and the magnetism of R (the Neel temperature doubles on going from x = 0 to 6 and the compounds become ferromagnetic for x = 8 with Curie temperatures of around 300 K). In pure TbMn12 the heat-capacity data shows a λ-type anomaly associated with the independent cooperative magnetic ordering of the R sublattice (∼5 K), while the anomaly related to the Mn magnetic ordering (∼100 K) is rather smooth, as observed in other itinerant magnetic systems such as YMn12. In contrast, the substitution of Fe for Mn leads, on the one hand, to a more localized magnetic behaviour of the 3d sublattice, and, on the other, to magnetic polarization effects between the 3d and 4f sublattices, together with the disappearance of the cooperative magnetic ordering of the R sublattice due to the breaking of the antiferromagnetic symmetry in the 3d sublattice. This is reflected in the heat-capacity curve through a smooth Schottky-like anomaly. In the case of Gd compounds the magnitude of the exchange molecular-field parameter has been deduced by fitting the magnetic contribution to the heat capacity within a simple mean-field model. From this analysis we found that this molecular field acting on the rare-earth site increases with the iron concentration, reaching values as large as 48 T for the concentration x = 6. A similar analysis of the heat capacity in the ordered phase on the Tb compounds also leads to an enhancement of the molecular field with increasing Fe content. These results allow checking the possible crystal-field parameters for these RFex Mn12−x compounds.

Transition metal distribution in the ErMn12−xFex (0 ⩽ x ⩽ 8) compounds

Abstract High-resolution neutron diffraction patterns have been collected at room temperature using ILL facilities for various ErMn 12− x Fe x compounds. Samples of composition x = 0, 2, 4, 6, 8 have been analysed in terms of the relative distribution of the transition metal (Mn or Fe) on the three available 8i, 8j and 8f sites of the structure type (SG: I4/mmm). Refinements of the crystal structures show that Mn atoms accommodate preferentially the 8i site contrarily to Fe atoms that fill majority the 8f ones. This observation is consistent with the criterial of relative atom size.