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Effect of randomness on anomalous Hall coefficient in antiferromagnet U2PdGa3

Tran V H

Materials Science Poland

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2008

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Vol. 26, No. 4

1069--1075

EN

The Hall effect has been studied for antiferromagnet U2PdGa3. In the paramagnetic state, the Hall data can be interpreted in terms of skew scattering theory for heavy-fermion systems. We observe a large contribution of anomalous Hall coefficient, indicating a dominated contribution of incoherent skew scattering by uranium 5f moments. Interesting behaviour of the RH(T) dependence is found at low temperatures. The RH(T) curve displays a plateau between T* = 12 and TN = 33 K, followed by a shoulder with further decreasing temperature. The appearance of the anomaly around T* suggests the existence of a new scattering mechanism, in addition to well known skew and jump-side scatterings. We compare the Hall data of U2PdGa3 with those observed for strongly correlated electron systems and with those of spin-glasses. Like the latter systems, non-zero spin chirality seems to play a considerable role in the anomalous Hall effect of U2PdGa3.

2

Observation of non-Fermi liquid behaviour in new Yb-based alloys

Tran V. H.

Materials Science Poland

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2007

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Vol. 25, No. 2

343--349

EN

In this contribution, after presenting the existing theoretical models, we discuss the evidence for non-Fermi liquid behaviour in Yb(Cu1-xSix)2-y that have been investigated for the last years in our Institute. The alloys crystallize in the hexagonal AlB2 type structure and exhibit a dramatic change in the electronic properties upon change of the electron concentration. Undoped YbSi2-y is an intermediate valent system, whereas the doping with 10% Cu ensures A(T) ??Tn, A(T) ??T and Cp ??T-1/2 dependences. Comparison of the data with the Griffiths phase model shows that this model can describe some of the observed results. We present also a study of the Hall effect. The Hall coefficient at 7 T is found to follow a lnT dependence below 10 K, thus showing the behaviour opposite to that in Fermi-liquid heavy-fermion systems.

3

Magnetism and electronictransport properties of Ce5CuPb3

Tran V. H., Jarmulska J., Miiller W.

Materials Science Poland

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2007

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Vol. 25, No. 2

327--332

EN

Polycrystalline sample of the ternary Ce-based compound Ce5CuPb3 was prepared and characterized using room temperature powder X-ray, EDX analysis as well as by magnetic susceptibility, electrical resistivity, and thermoelectric power measurements. The compound crystallizes in the Ti5Ga4-type structure (space group P63/mcm) with two different cerium sites: one at the 4d and the other at 6g position. The susceptibility shows two successive magnetic phase transitions at TC1 = 46.0 š 0.5 K and TC2 = 5.0 š 0.5 K. The double magnetic phase transition may be explained by two inequivalent magnetic sublattices of Ce3+ ions. The analysis of the magnetic data suggests that the transition at TC1 is of ferromagnetic origin and at TC2 is of ferrimagnetic one. Both the magnetic susceptibility, and electrical resistivity data imply the localized character of the Ce 4f electron. Above 150 K the ?(T) data follow the Curie-Weiss law with the effective moment žeff = 2.69 žB/Ce and the paramagnetic Curie temperature ?p equal to -21.8 K. The electrical resistivity exhibits a clear anomaly at TC1, below which the resistivity sharply decreases due to the reduction in the spin-disorder scattering. The thermoelectric power (TEP, S) of Ce5CuPb3 is negative over the temperature range studied, reaching the value of -14 žV/K at room temperature, and weakly varying with decreasing temperature down to TC1. A rapid change in TEP occurs below 25 K with the slope S/T as large as -0.27 žV/K2.

4

Magnetic phase diagram of the URh1-xRuxGe system

Miiller W., Tran V. H., Kondrat A.

Materials Science Poland

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2007

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Vol. 25, No. 2

391--397

EN

Magnetic phase diagram of the URhxRu1-xGe solid solutions has been reinvestigated by means of dc-magnetization, ac-susceptibility and electrical resistivity. We confirm ferromagnetic order only in alloys with x ??0.2. For a limited range of concentrations x between 0.3 and 0.35, we found features characteristic of short-range magnetic interactions. For compositions close to x = 0.4, non-Fermi liquid signature is observed in the low temperature resistivity. Thus, we report on the evolution of non Fermiliquid behaviour at a magnetic-nonmagnetic border, neighbouring with the region of the short-range interactions.

5

Hall effect in strongly correlated electron systems

Tran V.H.

Materials Science Poland

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2006

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Vol. 24, No. 3

669--673

EN

This work provides a brieft survey of the Hall effect data collected on some strongly correlated electron systems. The experimental results illustrate the behaviour of heavy-fermion system UCu5Al, heavy-fermion semiconductor U2Ru2Sn, ferromagnetic sueperconductor under pressure UGe2, and ferromagnet with a 2D weak localization effect UCo0.5Sb2.