Heavy-fermion characteristics inUCu5Alsingle crystals

Abstract

Electronic properties of the antiferromagnetic Kondo compound UCu 5 Al have been investigated through magnetic susceptibility, magnetization, specific heat, electrical resistivity, magnetoresistance, and Hall coefficient measurements on single-crystal and polycrystalline samples. UCu 5 Al orders antiferromagnetically below 16 K and shows a large magnetocrystalline anisotropy. In the paramagnetic state, pronounced incoherent Kondo interactions and crystal field effects are observed. At low temperatures, in spite of the lack of coherence, UCu 5 Al exhibits some characteristic properties of heavy-fermion systems, namely, an enhanced susceptibility, and enhanced electronic specific heat coefficient, revealing an enhanced effective electron mass. The specific heat and transport properties evidence a competition between the Kondo effect and the Ruderman-Kittel-Kasuya-Yosida interactions. This feature, together with the frustration of the magnetic interactions originating from atomic disorder appear to be important for the development of the heavy-fermion state in UCu 5 Al.

A new family of heavy-fermion compounds: U4TGa12 (T=Fe, Co, Rh and Pd)

“…Kinks are observed at 45 and 54.5 K for the Co and Rh-compounds, respectively, but no corresponding anomaly was found by any of the other techniques at these temperatures. U 4 FeGa 12 and U 4 PdGa 12 show different behavior with the appearance of upturns at 24.5 and 52 K, respectively, suggesting the opening of a gap as for example in UCu 5 Al [30]. U 4 PdGa 12 shows a change of slope around 43 K, more clearly and precisely seen on the temperature derivative curve (inset of Fig.…”

Magnetoresistivity studies of intermetallic uranium compounds and their impact on the understanding of exhibited phenomena

“…The earlier magnetization data, however obtained on very small single crystals [52], point to complex magnetic interactions in this compound having two magnetic atoms. The transition at T C can in principle be related to a ferromagnetic ordering of the iron atoms, while the anomaly at T t may reflect an ordering of the uranium moments in some different way.…”

“…Hence, it becomes clear that the magnetic field dependence of MR for UCu 5 Al or other antiferromagnets with a complex magnetic structures as UNiAl, demonstrates the presence of some additional scattering mechanism as is evidenced from a huge values of the measured MR. It is worthwhile noting that the TMR measured in UCu 5 Al for the current j directed parallel to the easy magnetization axis c is negligibly small [52].…”

Electron transport studies of UCu5Al and U1−Th Cu5Al

“…Recently, specific heat as well as electron transport measurements on single crystals have evidenced the existence of a competition between the Kondo effect and Ruderman-Kittel-Kasuya-Yosida interactions. This feature, together with the frustration of magnetic interactions, has been suggested to be important for the development of the HF state in UCu 5 Al [3]. In this contribution, we report on the electrical resistivity under high pressure up to 30 GPa performed on a UCu 5 Al single crystal and on high magnetic field studies up to 14 T of U 1Àx Th x Cu 5 Al solid solutions.…”

“…3. A remarkable feature of Dr/r(T)-curves observed for x=0.05 at m 0 H=10 T as well as for UCu 5 Al [2,3] is the occurrence of a minimum in Dr/r (T)-curves near T N . In magnetic fields up to 14 T, Dr/r(H) for all investigated solid solutions (x=0.05, 0,2, 0.3) is negative in the temperature range 2-100 K. A common feature is a curvature of Dr/r vs. H (Fig.…”