G. J. Nieuwenhuys

Spin glass behavior in URh2Ge2

URh_2Ge_2 occupies an extraordinary position among the heavy-electron 122-compounds, by exhibiting a previously unidentified form of magnetic correlations at low temperatures, instead of the usual antiferromagnetism. Here we present new results of ac and dc susceptibilities, specific heat and neutron diffraction on single-crystalline as-grown URh_2Ge_2. These data clearly indicate that crystallographic disorder on a local scale produces spin glass behavior in the sample. We therefore conclude that URh_2Ge_2 is a 3D Ising-like, random-bond, heavy-fermion spin glass.

CePd2Si2: a reduced-moment antiferromagnet

Abstract The compound CePd2Si2 has been investigated by neutron scattering, DC-susceptibility, specific-heat and resistivity measurements. CePd2Si2 crystallizes in the tetragonal 14/mmm structure. Below 8.5 K antiferromagnetic ordering takes place in a pattern consisting of ferromagnetic (110) planes with the spins perpendicular to the planes and alternating orientation in adjacent planes. The reduction of the Ce-moment from 2.55(5) μB for T ≧ 125 K to .66(6) μB at 4.2 K is larger than expected on basis of crystal-field calculations. The extra reduction is ascribed to a partial Kondo screening of the Ce-moments. An additional indication for partial screening comes from specific-heat measurements, which give a slightly enhanced value for the parameter γ (65(2) mJ/mol.K2). Resistivity measurements revealed a large anisotropy between a- and c-axes. In the neutron scattering experiments no critical scattering was observed, although the temperature dependence of the staggered magnetisation (critical exponent β = .37(3)) indicates a second-order phase transition at 9.2(5) K. We conclude that CePd2Si2 is a reduced-moment antiferromagnet with a Kondo temperature TK > TN.

High-field magnetization of heavy-fermion UPd2Al3

Abstract We report on high-field magnetization ( M ( B )) measurements ( B ≤ 35 T) of antiferromagnetic heavy-fermion UPd 2 Al 3 at liquid helium temperatures. The data taken on well-characterized single-crystalline samples reveal a large anisotropy. For a field directed in the hexagonal plane ( B || a -axis) a sharp jump, Δ M ⋍0.94μ B /U-atom, occurs at B c = 18.0 T, while for a field along the hexagonal axis (hard axis) the magnetization is small and almost linear up to 35 T. The jump at B c = 18.0 T for B || a reflects the antiferromagnetic phase boundary.

Structural and magnetic properties of UCo2Ge2

We have studied the effect of annealing on the structural and magnetic properties of UCo2Ge2 and thereby find the existence of two different crystallographic structures. The as‐cast, high‐temperature (HT) phase adopts a crystal structure with symmetry lower than I4/mmm; after annealing at 750 °C for 5 days the ThCr2Si2 (I4/mmm) structure is formed. Additionally, the length of the c axis in these tetragonal structures changes dramatically: whereas the HT phase has a c parameter of ≊9.3 A, the low‐temperature (LT), annealed phase has a much larger c axis of ≊9.9 A. This expansion of the unit cell greatly influences the magnetic properties of the material: while the LT sample orders antiferromagnetically at 174 K, the HT one does not order magnetically down to 350 mK. The antiferromagnetic transition is clearly indicated by our magnetization, resistivity and specific heat measurements.

Glassy Spin Dynamics in Non-Fermi-Liquid UCu5xPdx, x = 1.0 and 1.5

Local f-electron spin dynamics in the non-Fermi-liquid heavy-fermion alloys UCu5-xPdx, x = 1.0 and 1.5, have been studied using muon spin-lattice relaxation. The sample-averaged asymmetry function G(t) indicates strongly inhomogeneous spin fluctuations and exhibits the scaling G(t,H) = G(t/H(gamma)) expected from glassy dynamics. At 0.05 K gamma(x = 1.0) = 0.35+/-0.1, but gamma(x = 1.5) = 0.7+/-0.1. This is in contrast to inelastic neutron scattering results, which yield gamma = 0.33 for both concentrations. There is no sign of static magnetism approximately greater than 10(-3)(B)/U ion in either material above 0.05 K. Our results strongly suggest that both alloys are quantum spin glasses.

Metamagnetic transitions in cubic La(FexAl1-x)13 intermetallic compounds

Cubic NaZn13-type compounds of the form La(FexAl1-x)13 was stabilised with compositions between LaFe6Al7. For compositions above LaFe11.2Al1.8 (x=0.861) a low-temperature antiferromagnetic state is present in small external fields. However, upon increasing the field to a few tesla, an exceedingly sharp spin-flip transition with remarkably large hysteresis occurs to the fully saturated ferromagnetic state. The origins of this unusual metamagnetic transition are discussed in terms of the special crystal structure.

Disorder to order transition in the magnetic and electronic properties of URh2Ge2

We present a study of annealing effects on the physical properties of tetragonal single-crystalline

Hybridisation effects in UPt2Si2

{\mathrm{URh}}_{2}{\mathrm{Ge}}_{2}.

Magnetic behavior of U(3d)2Ge2 intermetallic compounds

This system, which in its as-grown form was recently established as the first metallic three-dimensional random-bond heavy-fermion spin glass, is transformed by an annealing treatment into a long-range antiferromagnetically ordered heavy-fermion compound. The transport properties, which in the as-grown material were dominated by the structural disorder, exhibit in the annealed material signs of typical metallic behavior along the crystallographic a axis. From our study

Magnetic and transport properties of some U3T3X4-compounds (T = Co, Ni, Cu and X = Sb, Sn)

{\mathrm{URh}}_{2}{\mathrm{Ge}}_{2}