4 research outputs found
Anomalous magnetic ordering in PrBa_2Cu_3O_{7-y} single crystals: Evidence for magnetic coupling between the Cu and Pr sublattices
In Al-free PrBa_2Cu_3O_{7-y} single crystals the kink in the temperature
dependence of magnetic susceptibility chi_{ab}(T), connected with Pr
antiferromagnetic ordering, disappears after field cooling (FC) in a field H ||
ab-plane. The kink in chi_c(T) remains unchanged after FC in H || c-axis. As a
possible explanation, freezing of the Cu magnetic moments, lying in the
ab-plane, caused by FC in H || ab, hinders their reorientation and, due to
coupling between the Pr and Cu(2) sublattices, ordering of the Pr^{3+} moments.
A field induced phase transition and a field dependence of the Pr^{3+} ordering
temperature have been found for both H || c and H || ab.Comment: 11 pages (LaTex with elsart.sty), 5 EPS figs. Accepted to Physica
Intergranular flux pinning in underdoped and overdoped R(1-x)CaxBa2Cu3Oz (R=Y,Gd; x=0,0.2) samples
The temperature dependences of AC magnetic susceptibility at different
magnetic field amplitudes and frequencies are investigated for underdoped and
overdoped R(1-x)Ca(x)Ba(2)Cu(3)O(7-delta)(R=Y; Gd and x=0; 0.2) polycrystalline
samples. The activation energy, Ea, for thermally assisted flux flow (TAFF) in
intergranular region is determined. It was established that a correlation
exists between the intergranular critical current and flux pinning activation
energy. In underdoped samples the intergranular current shows S-I-S behaviour
and the activation energy is small, while in overdoped samples the
intergranular current is changed to S-N-S type and the activation energy
increases. 2D pancake vortices are characteristic of underdoped samples, while
3D vortex system exists in overdoped samples. In fact we demonstrate that Ca
substitution not only increases carrier concentration, but improves
intergranular activation energy for TAFF.Comment: 20 pages including 7 figures and one Table. accepted in Physica