S. Cirafici

Magnetocaloric effect in the intermetallic compound Gd7Pd3

Abstract As a part of a current research concerning the physical characterisation of Rare Earth intermetallic compounds for magnetic refrigeration devices, the magnetocaloric properties of the Gd7Pd3 phase, which shows a ferromagnetic transition at 318 K, are presented. Heat capacity measurements have been performed in the 5–360 K temperature range and for applied magnetic fields up to 5 T (Tesla). Basing on the heat capacity data the isothermal entropy change ΔSM and the adiabatic temperature rise ΔTad have been calculated ( ΔSM =2.5 and 6.5 J/K kg and ΔTad=3.0 and 8.5 K at 320 K and respectively at 2 and 5 T). From the ΔSM vs. T plot the refrigerant capacity in the 260–360 K temperature range has been calculated to be 100 J/kg for an applied magnetic field of 2 T and 380 J/kg for an applied magnetic field of 5 T.

Crystal structure of R3Co8Sn4 compounds (R = Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y)

Abstract The R 3 Co 8 Sn 4 compounds (R=rare earth) have been synthesized and studied by single crystal and powder X-ray diffractometry. The phases with R=Pr, Nd, Sm, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y crystallize in the Lu 3 Co 7.77 Sn 4 structure type, but with full occupancy of all atomic positions, giving 3:8:4 stoichiometry in all cases except the lutetium phase. The studied phase was not found in the systems with La, Ce and Sc. These compounds should replace the previously reported RCo 3 Sn phases. The slightly anomalous dependence of the lattice constants on the rare earth size can be ascribed to strengthening of the Co–Sn bonds.

Structural anomaly in GdNiAl: a crystallographic, electric and magnetic investigation

Abstract Low temperature electrical resistivity and X-ray powder diffraction measurements showed a transformation point at about 200 K, attributed to a transition between two slightly different crystallographic forms of the ZrNiAl type. A corresponding anomaly was observed in the thermal behaviour of the magnetic susceptibility, and the results were analyzed in the framework of the RKKY theory. Ferromagnetic ordering occurs at 57 K, and two other transition temperatures, 30 and 14 K, were detected: these points, as already observed for TbNiAl, DyNiAl and HoNiAl may be imputed to order–order magnetic transitions.

Electrical resistivity measurements on some R5Si3 phases: R = Gd, Tb, Yb, Lu and Y

Abstract The electrical resistivity of the R 5 Si 3 phases with R = Gd , Tb , Yb , Lu , Y has been measured in the 10–800 K temperature range. The compounds of Gd and Tb exhibit one transformation point, which can be ascribed to magnetic transitions. The temperature dependence of the resistivity of Y 5 Si 3 and Lu 5 Si 3 has been described by a combination of the phonon contribution and an interband scattering term. For Yb 5 Si 3 , the different behaviour in the electrical resistivity, the low value of the magnetic moment as well as the anomalous values of the elementary cell constants can be explained assuming a mixed valent state of Yb: a divalent Yb ion in one site set and a trivalent Yb ion in the other site.

Magnetocaloric properties of Gd/sub 7/Pd/sub 3/ and related intermetallic compounds

From heat capacity measurements performed in the 5-350 K temperature range at 0- and 5-Tesla applied magnetic field on the intermetallic compounds Gd/sub 7/Pd/sub 3/ and Gd/sub 7/Pd/sub 2/Ni, and on the eutectic between Gd and Gd/sub 7/Pd/sub 3/ with composition Gd/sub 76/Pd/sub 24/, the main magnetocaloric properties of the alloys were obtained, namely the isothermal entropy change /spl Delta/S/sub M/, the adiabatic temperature rise /spl Delta/T/sub ad/ and the refrigerant capacity Q.

Physical properties of GdNiIn

Abstract Single-crystal X-ray analysis, electrical resistivity and magnetisation measurements were performed on GdNiIn. The compound is ferromagnetic with T c =93.5 K. From the hysteresis loop at 77 K, a remanence of 5 mT and a coercive field of 15 mT were obtained. The magnetic moment at 4.2 K shows a saturation value of 7.2 μ B .

Magnetism in R3Co8Sn4 compounds (R=Pr, Nd, Sm)

Abstract The magnetic properties of the R 3 Co 8 Sn 4 phases (R=Pr, Nd, Sm) were studied by AC and DC magnetic techniques. The three compounds order magnetically at 17, 37 and 83 K, respectively. Pr 3 Co 8 Sn 4 and Nd 3 Co 8 Sn 4 exhibit a spin reorientation transition under an applied field of 4 T (Pr) and 2 T (Nd), detected also by DC thermomagnetic measurements. The anomalous hysteresis loop of the Sm-phase is discussed in terms of a complete lack in the magnetic coupling of the two ferromagnetic phases: Sm 3 Co 8 Sn 4 and free Co. Dependence of the ferromagnetic transition temperature on Co–Co distances is discussed.

Physical properties of Ce2CoSn2

Abstract A complete physical characterisation, through specific heat, electrical resistivity and magnetization measurements was performed, in a wide temperature range, on the new phase Ce 2 CoSn 2 , which crystallizes in a very large fcc cell with a structure type similar to the Tb 117 Fe 52 Ge 112 one. From the real part of the AC susceptibility data a broad maximum can be observed at 7 K with an inflexion point, in agreement with the maximum observed in the imaginary part of the AC susceptibility, at a lower temperature (around 6 K). We hypothesize that the lower maximum can be attributed to an antiferromagnetic transition while the upper one could be related to the onset of a Kondo regime. The antiferromagnetic order is confirmed by magnetization measurements performed at 2 K in magnetic fields up to 9 Tesla: a metamagnetic transition could be observed around 0.4 Tesla. In the paramagnetic range the inverse of susceptibility follows a modified Curie–Weiss law, with an effective paramagnetic moment μ =2.89 μ B and a paramagnetic Curie temperature slightly positive. The heat capacity results suggest that this phase might be a heavy fermion system, with an electronic specific heat coefficient γ =1.3 J/K 2 mol. The electrical resistivity measurements exhibit a pronounced minimum at about 13 K and below this temperature a logarithmic Kondo-like behaviour is observed.

Electrical resistivity in the R5S3 systems (R La, Ce, Pr, Nd, Sm)

In our previous paper [1], the electrical resistivity (10-800 K) of some heavy RE silicides R 5 Si 3 (R≡Gd, Tb, Yb, Lu and Y) was examined: for Gd 5 Si 3 and Tb 5 Si 3 , a magnetic transition was found and a beterogeneous mixed valence was observed for Yb 5 Si 3 . In order to study the electronic behaviour of the R 5 Si 3 phases in a systematic way, the present work reports the electrical resistivity (10-800 K) of the light R 5 Si 3 compounds (R≡La, Ce, Pr, Nd and Sm)

Physical properties of ErFe4Ge2

Abstract A systematic study on the structural, electrical and magnetic properties of the ErFe 4 Ge 2 intermetallic phase was carried out. From scanning electron microscopy (SEM), differential scanning calorimetry (DSC) and high temperature electrical resistivity we found that the room temperature ferromagnetism may be ascribed to the presence of an impurity of eutectic composition Fe:Ge=70:30. Low temperature electrical resistivity and magnetisation measurements showed three magnetic transitions at 6.5, 21 and 40 K.