Elsevier

Physica B: Condensed Matter

Volume 404, Issue 19, 15 October 2009, Pages 2908-2911
Physica B: Condensed Matter

Magnetic properties around quantum critical point of CePt1-xRhx

https://doi.org/10.1016/j.physb.2009.07.139Get rights and content

Abstract

In order to investigate magnetic properties around a quantum critical point of CePt1-xRhx alloys, we have performed the ac-susceptibility (χac) measurements with field frequency ranging from ω/2π=0 (dc magnetization) to 1113 Hz for temperature down to 100 mK on polycrystalline CePt1-xRhx (x=0.5, 0.6). The in-phase component of χac exhibits a pronounced peak at Tf. The peak magnitude and Tf show significant field-frequency dependence. In addition, a staircaselike hysteresis loop of magnetization was observed below 200 mK. From the dynamical analyses of χac, we suggest that CePt0.5Rh0.5 and CePt0.4Rh0.6 can be described as cluster-glass systems.

Introduction

Recently much attention has been given to the study of quantum phase transitions (QPTs). QPT is defined as a phase transition which is driven at T=0 by changing non-thermal parameters, such as chemical substitution, pressure or magnetic fields. QPT can differ fundamentally from their classical counterparts at finite T where thermal fluctuations are important. In the f-electron compounds, a large number of investigations have been dedicated to the antiferromagnetic to paramagnetic QPTs [1]. In contrast, less attention has been given to the study of ferromagnetic quantum critical points (FQCPs). This may be attributable to the lack of suitable ferromagnetic (FM) Kondo-lattice systems.

Our previous study has revealed that CePt1-xRhx shows a continuous change in the ground state from ferromagnetic order of CePt (Tc~6K) to a non-magnetic valence-fluctuation state with increasing x [2]. From a simple extrapolation of Tc, we suggested that the FQCP is located at x~0.75(xc) in this system. We found a non-Fermi-liquid (NFL) like behavior for a wide x range above xc. The behavior is characterized by the power-law T dependence of specific heat (Cp) and dc magnetic susceptibility (χdc). On the other hand, a peak of Cp(T) observed at Tc for xxc is broaden for x0.5, reminiscent of spin-glass behavior. In this study, we present the investigation of the dynamical properties of CePt1-xRhx (x=0.5, 0.6) by means of ac-susceptibility at various frequencies and dc magnetization. The experimental results suggest that a cluster-glass state is stable at low temperature around xc.

Section snippets

Experimental procedure

Polycrystals of CePt1-xRhx (x=0.5, 0.6) were prepared by arc-melting using a water-cold copper crucible under an argon atmosphere. Powder X-ray diffraction analyses confirmed that the obtained crystals were in single phase with orthorhombic CrB-type structure. The scanning electron microscopy analysis confirmed homogeneity of the samples in a micrometric scale. The ac-susceptibility (χac) was measured in the frequency range between 2.6 and 1113 Hz using a standard Hartshorn bridge circuit

Results and discussions

The in-phase components of the ac-susceptibility χac(ω,T) of CePt0.5Rh0.5 and CePt0.4Rh0.6 measured at various frequencies are shown in Fig. 1. The χac exhibits a pronounced maximum at Tf. As ω increases, Tf shifts to higher temperature and the magnitude χac(Tf) decreases. It should be noted that the peak position of χac usually does not move with ω in such a low-frequency range, if the peak is associated with a normal ferromagnetic phase transition; the shift can usually be seen in the

Conclusions

In conclusion, our experimental results show that CePt0.5Rh0.5 and CePt0.4Rh0.6 can be described as a cluster-glass compounds. Tf and the magnitude χac(Tf) strongly depends on the field frequency. Furthermore, the frequency dependence of Tf follows the Vogel–Fulcher law, possibly providing a proof for cluster-glass behavior. The dc magnetization provides additional information on the cluster-glass state. MFC and MZFC for both concentrations exhibit a clear bifurcation at around Tf. In

Acknowledgments

This work is partly supported by a Grant-in-Aid for Scientific Research (B), 19340086 (2007) and the 21st Century COE Program on “Topological Science and Technology” from the Ministry of Education, Sports, Culture, Science and Technology of Japan.

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