Magnetic properties around quantum critical point of
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 by changing non-thermal parameters, such as chemical substitution, pressure or magnetic fields. QPT can differ fundamentally from their classical counterparts at finite 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 shows a continuous change in the ground state from ferromagnetic order of CePt () to a non-magnetic valence-fluctuation state with increasing [2]. From a simple extrapolation of , we suggested that the FQCP is located at in this system. We found a non-Fermi-liquid (NFL) like behavior for a wide range above . The behavior is characterized by the power-law dependence of specific heat () and dc magnetic susceptibility (). On the other hand, a peak of observed at for is broaden for , reminiscent of spin-glass behavior. In this study, we present the investigation of the dynamical properties of (, 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 .
Section snippets
Experimental procedure
Polycrystals of (, 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 () 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 of and measured at various frequencies are shown in Fig. 1. The exhibits a pronounced maximum at . As increases, shifts to higher temperature and the magnitude decreases. It should be noted that the peak position of usually does not move with 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 and can be described as a cluster-glass compounds. and the magnitude strongly depends on the field frequency. Furthermore, the frequency dependence of follows the Vogel–Fulcher law, possibly providing a proof for cluster-glass behavior. The dc magnetization provides additional information on the cluster-glass state. and for both concentrations exhibit a clear bifurcation at around . 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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