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We report the revisited magnetic phase diagram for the Kondo (ferromagnetic and antiferromagnetic) CeNi1−xCux series based on acdc magnetization, heat capacity, neutron diffraction and muon spectroscopy down to very low temperatures (~100 mK). An evolution from antiferromagnetism, observed for Cu-rich alloys (0.8 ≤ x ≤ 1), to clustered-ferromagnetism, seen for samples with 0.3 ≤ x ≤ 0.6, and then to spin-glass for 0.1 ≤ x ≤ 0.2, has been observed. The clustered-ferromagnetic phase emerges from a cluster-glass state without any indication of Curie temperature. For the samples adjacent to the magneticnonmagnetic crossover 0.1 ≤ x ≤ 0.2, only the cluster-glass state is observed due to the weakening of the RKKY interactions. We discuss the emerging phenomena taking into account the cluster-percolative scenario proposed for this series and the role of the interactions involved along the whole series. The proximity to a T = 0 K spin-glass quantum phase transition in the phase diagram is discussed.
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We present evidence for the existence of magnetic clusters of approximately 20 A in the strongly correlated alloy system CeNi 1-x Cux (0.7
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The study of the magnetic properties depending upon mechanical milling of the ferromagnetic polycrystalline TbAl(2) material is reported. Rietveld analysis of the x-ray diffraction data reveals a decrease in the grain size down to 14 nm and a -0.15% variation in the lattice parameter, after 300 h of milling time. Irreversibility in the zero field cooled-field cooled (ZFC-FC) dc susceptibility and clear peaks in the ac susceptibility between 5 and 300 K show that the long-range ferromagnetic structure is inhibited in favour of a disordered spin arrangement below 45 K. This glassy behaviour is also deduced from the variation of the irreversibility transition with the field (H(2/3)) and frequency. The magnetization process of the bulk TbAl(2) is governed by domain-wall thermal activation processes. In contrast, in the milled samples, cluster-glass properties arise as a result of cooperative interactions due to the substitutional disorder. The interactions are also influenced by the nanograin structure of the milled alloys, showing a variation in coercivity with the grain size, below the crossover between the multi- and single-domain behaviours.
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We study the magnetic ground state in La(2/3)Ca(1/3)Mn(1-x)Ga x O3 manganites, where a quantum critical point (QCP) has been theoretically predicted. The metallic ferromagnetic ground state for low Ga doping breaks down for x > or = 0.11, an insulating state being established at low temperatures. Long-range ferromagnetism coexists with short-range magnetic correlations in the concentration range 0.11 < or = x < or = 0.145 while only the short-range correlations survive for x > or = 0.16. We discuss the implications of such a QCP to the physics of manganites and compare to other QCP systems.
