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Magnetic structure of Dy[Fe(CN) 6 ]·4D 2 O was determined by means of neutron powder diffraction. The magnetic structure consists of Fe and Dy sublattices, which are coupled antiferromagnetically leading to overall ferrimagnetic ordering with the Curie temperature T c = 3.7 K. While for Fe-atoms the y -component of magnetic moment is large and the z -component is negligible, in the case of Dy-atoms the x -and the y -magnetic moment components are large and the arrangement of magnetic moments on Dy-sublattice is non-collinear. In this magnetic structure the y -components of magnetic moment on Dy and Fe atoms are anti-parallel. Our magnetic structure refinement yields the moment value of 11.06 μ B for dysprosium and 1.61 μ B for iron atoms.

La0.67Pb0.33(Mn1-xCox)O3-δ ceramics with x=0, 0.01, 0.03, 0.06, 0.1 and 0.15 have been prepared in a two-step procedure. Precursor gels were made by the wet chemical malic acid method. The gels were calcined and then converted into ceramics by heat treatment at 950 °C and 1000 °C in air. X-ray diffraction showed that the compounds were phase pure. The crystal structure symmetry of the compounds was confirmed to be rhombohedral (space group R3c) for the whole investigated range of x. All compounds undergo a paramagnetic–ferromagnetic phase transition between 335 K and 225 K. The basic magnetic characteristics such as the Curie temperature $\mathit{T}_{\mathrm{C}}$ , the paramagnetic Curie temperature θ, the effective magnetic moment $\mathit{\mu}_{\mathrm{eff}}$ and the saturated magnetization $\mathit{\mu}_{\mathrm{s}}$ decrease with increasing Co doping. The ferromagnetic transition is accompanied by an anomaly in the electrical resistance for all compounds. The high-temperature insulator–metal transitions ( $\mathit{T}_{\mathrm{p}}$ ) do not coincide with the relevant $\mathit{T}_{\mathrm{C}}$ . A large magnetoresistance peak of about 15% was observed for all compounds at $\mathit{T}_{\mathrm{C}}$ .

Heat capacity data of U 3 Al 2 Si 3 single crystal exhibit a maximum at 38 K connected with a transition to a magnetically ordered state. For a full description of the electron part we use γ 0 = 145 mJ/mol K 2 and for the phonon part of the specific heat we used the harmonic approximation of the phonon spectrum including both the Debye model with T D = 296 K and the Einstein model with T E = 136, 249 and 438 K. The heat capacity data below the magnetic transition down to 2 K fit very well within the model introducing the energy gap A = 39 K in the dispersion relation of magnons. An upturn of the C/T(T) curve, found below T = 2 K, can not be fully attributed to the nuclear Schottky contribution. The electronic heat capacity coefficient (γ 230 mJ/mol K 2 is enhanced and varies between 0.15 K and 12 K as the square root of T.

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.

We present results of neutron scattering experiments on frustrated antiferromagnet HoB12 above and below Neel temperature TN. Diffuse scattering patterns indicate that above TN=7.4 K pronounced correlations between neighboring magnetic moments of Ho-ions appear, similar to one-dimensional (1D) magnets. Moreover, the diffuse scattering patterns show a symmetry reduction from fcc to simple cubic. Analogous behavior in three dimensional (3-D) systems is not known, although it was predicted by theory. Results below TN and in applied magnetic field, on the other hand, reveal three amplitude-modulated incommensurate magnetic structures in this compound. The role of various interactions leading to this behavior (above and below TN) is being discussed. Additional attention is paid also to ρ(T) resistivity dependencies in various magnetic fields close to and above the quantum critical point.

We measured electrical resistivity in U 1− x Ce x Ru 2 Si 2 single crystals (0.00≤ x ≤0.050) at ambient pressure and at hydrostatic pressures up to 9 kbar. Our measurements show strong anisotropy, with the in-plain resistivity ρ a much higher than ρ c parallel to the c -axis. The substitution of U with Ce in URu 2 Si 2 reduces the transition to a Kondo coherent state and the Neel temperature. The minimum in the Cr-like anomaly becomes more prominent but the characteristic shape of the anomaly vanishes. Low temperature characteristic features of URu 2 Si 2 , superconductivity and Fermi-liquid behaviour, vanish very rapidly with Ce substitution. The Neel temperature T N increases by applying hydrostatic pressure with pressure coefficients ∂ T N / ∂ p =0.08±0.02 K kbar −1 for x =0.00 and ∂ T N / ∂ p =0.13±0.02 and K kbar −1 for x =0.025.

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.

Neutron and EPR Study of Cu(tn)Cl2 a Two-Dimensional Spatially Anisotropic Triangular-Lattice Antiferromagnet R. Tarasenkoa,∗, A. Orenda£ova, E. ƒiomar, S. Ma a2, M. Orenda£, V. Zele¬ak, V. Pavlik, K. Siemensmeyer, S. Zvyagin, J. Wosnitza, A. Feher Institute of Physics, Faculty of Science, P.J. ’afarik University, Park Angelinum 9, 041 54 Ko2ice, Slovakia Helmholtz-Zentrum Berlin, Hahn-Meitner Platz 1, D-14109 Berlin, Germany Institute of Chemistry, Faculty of Science, P.J. ’afarik University, Moyzesova 11, 041 54 Ko2ice, Slovakia Institute of Experimental Physics SAS, Watsonova 47, 040 01 Ko2ice, Slovakia Dresden High Magnetic Field Laboratory (HLD), Helmholtz-Zentrum Dresden-Rossendorf and TU Dresden, D-01314 Dresden, Germany

We have investigated the magnetic structure of HoB 12 , ErB 12 and TmB 12 by neutron diffraction on isotopically enriched single-crystalline samples. Results in zero field as well as in magnetic field up to 5 T reveal modulated incommensurate magnetic structures in these compounds. The basic reflections can be indexed with q = (1/2±δ, 1/2±δ, 1/2±δ), where δ = 0.035 both for HoB 12 and TmB 12 and with q = (3/2±δ, 1/2±δ, 1/2±δ), where δ = 0.035, for ErB 12 . In an applied magnetic field, new phases are observed. The complex magnetic structure of these materials seems to result from the interplay between the RKKY and dipole-dipole interaction. The role of frustration due to the fcc symmetry of dodecaborides and the crystalline electric field effect is also considered.

The electrical resistances of oriented single crystals of TmB12 and HoB12 in the temperature range 1.6–10 K are reported. From the temperature derivatives of the resistances the corresponding Neel temperatures TN have been determined. The temperature dependence of the d.c. magnetic susceptibility of HoB12 down to 5 K has also been measured and confirms the antiferromagnetic nature of the phase transition.

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.

Charles University, Faculty of Mathematics and Physics Department of Electronic Structures Ke Karlovu 5, 121 16 Prague 2, Czech Republic Frequency dependence of χ′′(T ), different position of a maximum in χ′′(T ) for different crystal orientations, hysteretic behavior between magnetization measurements in zero-field cooling and field coolding regime are attributed to strong magneto-crystalline anisotropy of PrNi ferromagnetic single crystal with TC = 20.5 K, which is driven by crystal field effect. Applied pressure shifts TC to higher temperatures (dTC/dp = 1 K/GPa). Susceptibility follows the Curie–Weiss law except for b-axis, which is hard magnetic axis. An anisotropic behavior was seen in resistivity measurements with the largest difference between b-axis and c-axis. Resistivity below TC can be described by power law with ρ ∼ T 2.24 and is field dependent with a positive magnetoresistance.