Magnetic ground state ofCeNi1−xCux: A calorimetric investigation

Abstract

CeNi 1−x Cu x is a substitutional magnetic system where the interplay of the different magnetic interactions leads to the disappearance of the long-range magnetic order on the CeNi side. The existence of inhomogeneities ͑spin clusters or phase coexistence͒ has been previously detected by magnetization and muon spin relaxation ͑SR͒ spectroscopy measurements. These inhomogeneities are always observed regardless of the different preparation methods and must, then, be considered as intrinsic. We present a detailed specific heat study in a large temperature range of 0.2 to 300 K. The analysis of these data, considering also previous neutron scattering, magnetic characterization, and SR results, allows us to present a convenient description of the system as inhomogeneous on the nanometric scale. Two regimes are detected in the compositional range depending on the dominant Ruderman-Kittel-Kasuya-Yosida or Kondo interactions. We propose that the longrange magnetic order at low temperatures is achieved by a percolative process of magnetic clusters that become static below the freezing temperature T f . In this scenario the existence of a quantum critical point at the magnetic-nonmagnetic crossover must be discarded. This situation should be considered as an example for other substitutional compounds with anomalous magnetic or superconducting properties.

Theory of the Kondo lattice: competition between Kondo effect and magnetic order

“…Thus, a SG-Kondo transition has been observed experimentally with increasing concentration in disordered alloys around the QCP. Recent experiments performed in CeNi 1 À x Cu x alloys have shown that the phase diagram of these alloys is more complicated [51,52]. In fact, when temperature decreases, for alloys with 0.7 > x > 0.1, there appears a ''cluster spin glass'' phase presenting magnetic inhomogeneities, rather than a classical SG phase.…”

The Kondo Lattice Models and Magnetism for Cerium and Uranium Systems

“…(6) seems to be more adequate here than the "average" description used for example in the Sherrington-Kirkpatrick approach [45,47]. However, a real improvement will be provided by trying to describe better the clusters which are yielding the CG state with ferromagnetic correlations and the IFM state and then the observed percolative CG-IFM transition observed with decreasing temperature [37,38]. A first approach had been proposed to obtain clusters with intrasite Kondo interactions and both intra-and inter-cluster magnetic interactions within the Sherrington-Kirkpatrick approach [53].…”

“…The first studied case is the CeNi x Cu 1−x alloys [35][36][37][38][39], but recently the CeRh x Pd 1−x alloys [40,41] have been also studied and a new cluster glass state has been identified recently in these two cases. In fact, a careful experimental study of CeRh x Pd 1−x alloys shows the presence of the Kondo clusters near x = 0.8 when the ferromagnetic phase is very close to disappear [40].…”

“…But, very recently, these alloys have been investigated by µSR spectroscopy or small angle neutron scattering (SANS) or magnetic experiments leading to the determination of hysteresis loops [37][38][39]. The experimental results have been analyzed in terms of "cluster glass" (CG).…”

Kondo Lattice Models for Rare-Earth and Actinide Systems

“…However, a real improvement will be provided by trying to describe better the clusters which are yielding the cluster-glass state (CG) with ferromagnetic correlations and the IFM state and also the observed percolative CGIFM transition observed with decreasing temperature [46,47]. A rst approach had been proposed to obtain clusters with intrasite Kondo interactions and both intra-and inter-cluster magnetic interactions within the SherringtonKirkpatrick approach [58].…”