D. Drobac

Ground-state order and spin-lattice coupling in tetrahedral spin systems Cu 2 Te 2 O 5 X 2 ( X = Br or Cl)

High-resolution ac susceptibility and thermal conductivity measurement on Cu2Te2O5X2(X=Br,Cl) single crystals are reported. For Br-sample, sample dependence prevents to distinguish between possibilities of magnetically ordered and spin-singlet ground states. In Cl-sample a three-dimensional transition at 18.5 K is accompanied by almost isotropic behavior of susceptibility and almost switching behavior of thermal conductivity. Thermal conductivity studies suggest the presence of a tremendous spin-lattice coupling characterizing Cl- but not Br-sample. Below the transition Cl-sample is in a complex magnetic state involving AF order but also the elements consistent with the presence of a gap in the excitation spectrum.

Intra- and intergrain effects in a.c. susceptibility of YBaCuO ceramics

Abstract The dependence of the initial magnetic susceptibility on the magnetic field, frequency and density has been investigated for several ceramic YBa 2 Cu 3 O 7 samples. The superconducting transitions show invariably two steps, associated with the grain and bulk (shielding) effects respectively. The width of transition decreases, whereas the lower critical field increases, with increasing density.

The Effect of Inhomogeneity on the Magnetic Transition in Glassy Ni-Fe alloys

The magnetic susceptibility of several FexNi80-xB18Si2 alloys (3 ≤ x ≤ 15) has been studied around and above the Curie temperature. The magnetic inhomogeneity of these alloys sharply increases on approaching the percolation threshold (xc 2.5), as evidenced by the enhanced non-monotonic variation of the effective critical exponent, γ*(T), and by the increasing assymetry of the Arrott-Belov-Kouvel plots. The tendency towards homogeneous magnetism for x ≥ 20 is deduced. The results are compared with those for other glassy Fe-Ni alloys and the origin of the magnetic inhomogeneity discussed.