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CePt 3 Si is a novel ternary compound exhibiting antiferromagnetic order at T N ≈ 2.2 K and superconductivity (SC) at T c ≈ 0.75 K . Large values of H c 2 ′ ≈ - 8.5 T / K and H c 2 ( 0 ) ≈ 5 T indicate Cooper pairs formed out of heavy quasiparticles. The mass enhancement originates from Kondo interaction with a characteristic temperature T K ≈ 8 K . NMR and μ SR measurements evidence coexistence of SC and long-range magnetic order on a microscopic scale. Moreover, CePt 3 Si is the first heavy fermion SC without an inversion symmetry. This gives rise to a novel type of NMR relaxation rate 1 / T 1 which is very unique and never reported before for other heavy fermion superconductors. Studies of Si/Ge substitution allow us to establish a phase diagram.

The crystal and magnetic structures of U(Pd 1− x M x ) 2 Ge 2 compounds with M=Fe, Co, Ru are studied by neutron powder diffraction and μSR. The effects of M doping and external applied pressure on the crystal and magnetic structures are compared. We find that even at small M-doping level the magnetic structure drastically changes, while the values of the lattice parameters and interatomic distances change only slightly. In contrast, a high external pressure modifies the crystal structure more significantly, while the magnetic structure remains the same. These observations allow us to conclude that the drastic changes of magnetic structure of U(Pd 1− x M x ) 2 Ge 2 compounds with increased M doping could result from modifications of the RKKY indirect exchange interactions owing to a variation of conduction-electron number per U atom, rather than from lattice contraction.

We report lSR studies on a Ce 3 Pd 20 Si 6 polycrystalline sample. Zero-"eld measurements were undertaken to gain information on the magnetic ordering at low temperatures. Below 0.4 K the increase of the muon-spin depolarization rate re#ects the development of a quasi-static ordering of magnetic moments of electronic origin probably randomly oriented. In transverse-"eld studies a clear frequency shift was observed. This fact may be ascribed to the increase of the total-magnetic moment of the superparamagnetic cube containing 8 Ce2 atoms and their ferromagnetic ordering with decreasing temperature. ( 2000 Elsevier Science B.V. All rights reserved.

The low-temperature state of U ( Pd 1−x Fe x ) 2 Ge 2 (x=0.01, 0.02) is transformed from simple anti-ferromagnetism AF (x=0.02) with a propagation vector k =[0 0 1] to the modulated longitudinal spin density wave LSDW (x=0.01) with k =[0 0 3 4 ] . ZF-μSR showed that in the sample with x=0.01 the magnetic moments of uranium atoms in two magnetically nonequivalent positions (0 0 0) and (0 0 1) have different temperature dependencies. The results are discussed in the model of a superposition of square and sine shape of modulation in comparison with neutron diffraction data. It is shown, that the observed temperature behavior of moments can be connected with the temperature variation of the initial phase of LSDW modulation.

A novel ternary compound has been found at the 1:2:1 position among the Yb–Pd–Si phases, where YbPd 2 Si crystallises in the ordered Fe 3 C -structure. YbPd 2 Si is characterised by Kondo lattice features at higher temperatures and, presumably, antiferromagnetism at 2.1 K. A quasi-quartet crystal field ground state governs the physics at low temperature.