Anisotropy of the diamagnetic susceptibilities of diphenyl carbinol

Abstract

ErRh 4 B 4 is a reentrant superconductor and exhibits a superconducting transition at 8.4 K and a ferromagnetic one at 0.9 K ; its structure is Primitive Tetragonal (PT) P4 2 /nmc, a1 = 5.292 A, c 1 = 7.379 A). The same compound exists also in another form with a Body Centered Tetragonal cell (BCT) (14 1 /acd, a 2 = 7.461 A, c 2 = 14.804 A) ; in this latter structure, the superconducting transition still 6ccurs but the magnetic order is antiferromagnetic [Iwasaki H., lkebe M. and Muto Y. (1986) Phys. Rev. B ;u, 4669-4679 and Iwasaki H. and Muto Y. (1986) Phys. Rev. B;u, 4680-4685 Our results show that a disordered ErRh 4 B 4 form exists, the structure of which is closely related to the BCT one.Single crystals were grown from the melt either in an induction furnace or in a tri-arc furnace under purified argon atmosphere. Samples obtained have a structure related to the BCT, orthorhombic and PT phases, the pseudo cubic sublattice a -7.45 A (a-a1-J2-a 2 -a3 -c1 -c 2 12 -c:, -b3/3) is maintained. Superstructure reflections show that this structure is closer to the BCT one. However the observed diffuse streaks indicate that the order of the Rh 4 B 4 bitetrahedra is broken along the c axis. The intensity of the diffuse streaks and the modulations of their intensity can change with the sample and the preparation. Many of these compounds are short-range ordered, the corresponding modulation propagation vector length along c is close to 4a.ErRh 4 B 4 structures can be schematized as two interpenetrated f.c.c. sublattices of erbium atoms and Rh 4 B 4 bitetrahedra. Tl1ere is only a change of the order and the orientation of the Rh 4 8 4 bitetrahedra between the different structural forms. The short range ordered phase we have studied has a structure which can be deduced from the three other ordered phases.The disorder consists of a rr./2 ± e rotation of Rh 4 B 4 bitetrahedra which results in a slight variation of the pseudo cubic lattice parameter and of the Er-Er distances. The disorder and the short range order we have observed could explain tile different physical properties measured in our samples and in those of Iwasaki H. et a!. The diamagnetic susceptibilities of diphenyl carbinol crystals were measured to study the effect of intermolecular hydrogen bonds formed between the carbinol groups of the molecules. The two molecules present in the asymmetric unit are centrosymmetrical. The intermolecular hydrogen bonds are in the form of a chain along the c-axis. The ellipsoid of the diamagnetic susceptibility coincides with the crystallographic axes. The observed high value of the diamagnetic susceptibility along the c-axis is due to the planal'i ty of the benzene rings of-the molecules in the ~-plane.