ABSTRACT
Based on magnetization, specific heat, magnetostriction and neutron-diffraction studies on single-crystal TbCo(2)B(2)C, it is found out that the paramagnetic properties, down to liquid nitrogen temperatures, are well described by a Curie-Weiss behavior of the Tb(3+) moments. Furthermore, below T(c) = 6.3 K, the Tb sublattice undergoes a ferromagnetic (FM) phase transition with the easy axis being along the (100) direction and, concomitantly, the unit cell undergoes a tetragonal-to-orthorhombic distortion. The manifestation of an FM state in TbCo(2)B(2)C is unique among all other isomorphous borocarbides, in particular TbNi(2)B(2)C (T(N) = 15 K, incommensurate modulated magnetic state) even though the Tb ions in both isomorphs have almost the same crystalline electric field properties. The difference among the magnetic modes of these Tb-based isomorphs is attributed to a difference in their exchange couplings which are in turn caused by a variation in their lattice parameters and in the position of their Fermi levels.
ABSTRACT
The low-temperature properties of single-crystal CeCoGe were investigated by specific heat C(T,H), magnetoresistivity ρ(T,H), and differential susceptibility measurements χ(T,H). The zero-field low-temperature specific heat evolves as C = γT+ßT(3) = 42T+23.5T(3) mJ mol(-1) K(-1). On comparing its γ = 42 mJ mol(-1) K(-1) with that of LaCoGe (12 mJ mol(-1) K(-2)) it is inferred that both 3d (Co) and 4f (Ce) orbitals contribute to the density of states at the Fermi level. Assuming that its phonic contribution to the specific heat is similar to LaCoGe (ß = 0.5 mJ mol(-1) K(-4)), then the extra cubic term in the specific heat (23T(3) mJ mol(-1) K(-1)) must be due to magnon excitation within the antiferromagnetically ordered state, T
ABSTRACT
Vitreous examinations using the three-mirror Goldmann and the preset El Bayadi-Kajiura lenses were performed on 222 eyes. The presence of posterior vitreous detachment, vitreous traction, liquefaction, lacunae, and cells was noted. Clinical findings using the two lenses differed in 10% of the variables studied. The accuracy of the El Bayadi-Kajiura technique was confirmed by clinical and histological examination of 20 animal eyes with experimentally altered vitreous. The Goldmann lens afforded examination of peripheral vitreous and better identification of cells in the vitreous, whereas the El Bayadi-Kajiura lens permitted better visualization of complex vitreoretinal relationships.