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We have studied the magnetic and electrical properties of non-stoichiometric U1+xNi1+yAl compounds. It has been shown that both the positive and negative deviations from the stoichiometry lead to suppression of magnetically ordered state, to the broadening of the phase transition and to the occurrence of a region with high degree of short range magnetic ordering between 20 K and 50 K. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

We present an analysis of the powder neutron diffraction patterns taken from the Dy[Fe(CN)6].4D2O at room temperature and in the temperature range 1.6 - 40 K. The deuterium positions were localized by means of combination of direct and reciprocal space methods and crystal structure of the compound was refined using the Rietveld method. The knowledge of the complete crystal structure, including the deuterium atoms positions, enables further investigation of magnetic structure of these types of materials from the neutron diffraction experiments. The investigated phase was found to order magnetically bellow 2.8 K. The diffraction patterns taken at temperatures 1.76 K - 9.63 K show gradual development of magnetic moment as temperature decreases.

A transition to magnetic ordered state has been investigated by AC-susceptibility measurements on a single crystal of U3Al2Si3 at ambient pressure and at high pressure up to p=6.7 kbar. The transition to the magentic ordered state in U3Al2Si3 is accompanied with a relatively wide double peak between T=25 K and T=50 K in AC-susceptibility data. A pronounced maximum at about Tc1M=37 K and a local maximum at about Tc2M=45 K are both shifted to lower temperatures by applied pressure with different pressure coefficients ∂Tc1M/∂p=−0.9±0.1 K kbar−1 and ∂Tc2M/∂p=−0.5±0.1 K kbar−1, respectively.

Heat capacity and magnetization were measured on crystal Ce 5 Ni 2 Si 3 grown by Czochralski method. The compound is antiferromagnetic below T N =6.7 K. The irreversibility in zero-field cooling and field-cooling curves, deviation from Curie Weiss law and ferromagnetic-like behavior in magnetization curves at low fields were observed. Anisotropy in magnetization dependencies and large Shottky contribution to specific heat are attributed to crystalline electric field effect. The enhancement of C / T ( T ) at low temperatures can be described by an empirical formula γ=γ 0 (1+ A exp(− BT )).

The influence of the mechanical milling and subsequent thermal relaxation on magnetic and superconducting behaviour of YBa2(Cu1_ yFex)3O system has been studied. Two methods of heat treatment were used: Set I — slow cooling from 980 ° C in flowing O2 and Set H — reducing at 770°C in flowing Are followed by reoxidation in flowing O2 below 400°C. The transition to superconductivity, diamagnetic response, critical current density and the effective magnetic moment in the normal state have been estimated. Our measurements indicate that the reducing atmosphere preparation is less detrimental on superconducting properties. The results are discussed in terms of occupancy Cu sites by Fe and redistribution of oxygen atoms.

The influence of the mechanical milling and subsequent thermal relaxation on the superconducting and magnetic properties of the YBa 2 (Cu 1−y Fe y )O 7−x compounds (y=0.00, 0.02 and 0.04) have been studied. Changes of the transition temperature T c , the diamagnetic response, the effective magnetic moment and the Curie paramagnetic temperature have been estimated. Results are associated with the arrangement of oxygen atoms during milling and the thermal relaxation.

Superconducting properties of Pb 0.4 Bi 1.8 Ca 2.0 Sr 2.0 Cu 3 O y and Pb 0.3 Bi 1.7 Ca 2.4 Sr 1.6 Cu 3 O y ceramics were studied by measurements of magnetization and electrical resistivity. The activation energy of pinning at 4.2 K for Pb 0.3 Bi 1.7 Ca 2.4 Sr 1.6 Cu 3 O y was found to be higher than for Pb 0.4 Bi 1.8 Ca 2.2 Sr 2.0 Cu 3 O y ; at 77 K we observed the opposite tendency. The critical current density was estimated to be of order 10 6 A/cm 2 and 10 3 A/cm 2 at 4.2 K and 77 K, respectively. The irreversibility line was found to vary as a power law (1− T in / T c ) = AH n , where A and n are sample dependent constants related to the flux pinning properties of the samples.