Search

Neutron scattering experiments have been carried out on the heavy fermion antiferromagnetic (AFM) superconductor CePt3Si with TN = 2.2 K and TSC = 0.75 K. We observed clear AFM Bragg reflections with Q0 = (001/2) below and above TSC, indicating microscopic coexistence of AFM order and heavy fermion superconductivity. The AFM structure, of two interleaved ferromagnetic sublattices of local Ce 4f moments, has inversion symmetry under simultaneous space–time reversal. However, hybridization with Pt and Si breaks this degeneracy and a combination of these two competing effects may be relevant to an understanding of the simultaneous occurrence of superconductivity and AFM order. The observed magnetic moment 0.16(1) μB/Ce is strongly reduced from the Curie–Weiss effective moment 2.54 µB/Ce. Clear crystal field excitations at 1 and 24 meV were observed. The magnetic susceptibility can be well explained in a level scheme assuming the Γ7 ground state, Γ6 and Γ7 first and second excited states, respectively.

We have carried out de Haas–van Alphen (dHvA) experiments on a ferromagnet CeRh3B2 with an extremely high Curie temperature K and a non-4f reference compound LaRh3B2. The dHvA data of LaRh3B2 are well explained by the results of energy band calculations. The topology of the Fermi surfaces in CeRh3B2 is found to be very similar to that of LaRh3B2, possessing wavy but flat Fermi surfaces in the basal plane. Observation of a quasi-one-dimensional electronic state is the first such case in a rare earth compound.

CeRh3B2 is a ferromagnet with an unexpectedly high Curie temperature and low saturation magnetic moments. The origin of its unusual magnetic behaviour remains unelucidated despite various investigations performed in the last two decades. Here we present magnetic results obtained on high-quality single crystals over a wide temperature range. Some new magnetic features are uncovered and possible approaches to explaining its magnetism are briefly discussed.

The spin-polarized electron momentum distribution (magnetic Compton profile: MCP) of ferromagnetic CeRh3B2 has been measured using the magnetic Compton scattering technique at 10 K for the [110] direction. In this compound, the orbital moment dominates the magnetization. An analysis of the MCP reveals that the Ce 4f and Ce 5d spin moments are aligned parallel with a value of −0.68 ± 0.08 and 0.41 ± 0.04μB, respectively, while Rh 4d electrons do not carry any significant spin moment. The ratio of orbital to spin moments for Ce 4f electrons, which has been determined from comparison of the present data with recent polarized neutron diffraction data, is rather smaller than that for Ce3+ ions. This result implies strong hybridization of the Ce 4f orbital with the orbitals on the surrounding ions.

We have studied the effect of pressure on the electrical resistivity of a high-quality single crystal CeAgSb2 which has a small net ferromagnetic moment of 0.4μB/Ce. The magnetic ordering temperature Tord = 9.7 K decreases with increasing pressure p and disappears at a critical pressure pc 3.3 GPa. The residual resistivity, which is close to zero up to 3 GPa, increases steeply above 3 GPa, reaching 55μΩ cm at pc. A huge residual resistivity is found to appear when the magnetic order disappears.

Rietveld analysis was performed for the intermetallics Yb3Co4.3Sn12.7 and Yb3Co4Ge13 crystallizing with the closely related structure types, Yb3Rh4Sn13 and Yb3Co4Ge13. Below Tc = 3.4 K Yb3Co4.3Sn12.7 crosses over into a type-II superconducting ground state with Hc2(0)~2.5 T. Yb3Co4Ge13 stays in the normal state down to 300 mK. The γ value of 2.3(2) mJ gat-1 K-2 and the Debye temperature ΘD = 207(5) K deduced from the specific heat as well as Tc correspond to that of elementary Sn, thus indicating conventional BCS superconductivity. Hydrostatic pressure applied to Yb3Co4.3Sn12.7 reveals both an overall decrease of the absolute resistivity values, as well as a decrease of Tc, which vanishes for a critical pressure below 10 kbar. The magnetoresistance of both Yb-based compounds is positive at low temperature but does not exceed 8% in fields of 12 T. The Seebeck coefficient has a maximum value of about 18 µV K-1 at T~250 K. LIII and magnetic susceptibility measurements reveal intermediate valence: 2.66(3) and 2.18(3) for Yb3Co4Ge13 and Yb3Co4.3Sn12.7, respectively.

Novel ternary compounds, M(2)Pd(14+x)B(5-y) (M = La, Ce, Pr, Nd, Sm, Eu, Gd, Lu, Th; x∼0.9, y∼0.1), have been synthesized by arc melting. The crystal structures of Nd(2)Pd(14+x)B(5-y) and Th(2)Pd(14+x)B(5-y) were determined from x-ray single-crystal data and both are closely related to the structure type of Sc(4)Ni(29)B(10). All compounds were characterized by Rietveld analyses and found to be isotypic with the Nd(2)Pd(14+x)B(5-y) type. Measurements of the temperature dependent susceptibility and specific heat as well as the temperature and field dependent resistivity were employed to derive basic information on bulk properties of these compounds. The electrical resistivity of M(2)Pd(14+x)B(5-y), in general, is characterized by small RRR (residual resistance ratio) values originating from defects inherent to the crystal structure. Whereas the compounds based on Ce, Nd, Sm and Gd exhibit magnetic order, those based on Pr and Eu seem to be non-magnetic, at least down to 400 mK. While the non-magnetic ground state of the Pr based compound is a consequence of crystalline electric field effects in the context of the non-Kramers ion Pr, the lack of magnetic order in the case of the Eu based compound results from an intermediate valence state of the Eu ion.