Magnetization measurements in fields up to 38 T performed at low temperature on single crystals of the hexagonal Pr(Nit_xCox) s compounds for x 0, 0.05, 0.10 and 0.20 are presented. In PrNi s we observe highly original behaviour predicted by the knowledge of the Crystalline Electric Field parameters and arising from the existence of a non-magnetic singlet ground state; namely transitions associated with the field induced "anticrossing" and "crossing" of the two lowest states along the [100] and [120l directions, respectively. The measurements performed on the other compounds have allowed us to study the dependence of this behaviour on Co substitutions.

We have studied the magnetic properties of R3Ge4 compounds with R = Dy and Er by means of specific heat measurements. Both compounds show specific heat anomalies indicative of a two-step magnetic ordering upon cooling. The results are discussed together with neutron diffraction data.

CeRhSb is a mixed-valent compound in which a gap opens up in the electronic density of states below a temperature of about 10 K. Earlier studies on Pd substitution at the Rh site in this compound showed that the gap is suppressed for around 10% Pd and an antiferromagnetic ground state emerges with higher Pd substitution. Here, we report heat-capacity results on some of these samples, namely, CeRh0.8Pd0.2Sb and CeRh0.7Pd0.3Sb. We observe a sharp rise in C-4f/T of CeRh0.7Pd0.3Sb starting at around 5 K with a peak at about 2.5 K, which confirms the antiferromagnetic ordering in this compound. An entropy change of 2.5 J/mol K is obtained for the ordering. Above the Neel temperature, the value of the electronic specific heat coefficient gamma is found to be about 40 mJ/mol K-2. In CeRh0.8Pd0.2Sb, C-4f/T is found to rise below 10 K down to the lowest temperature of measurement, namely, 1.5 K with a gamma value of about 40 mJ/mol K-2. The rise may be due to non-Fermi-liquid behavior or could be due to impending magnetic order in the compound below 1.5 K. [S0163-1829(98)02726-X].

The magnetic behavior of some ${\mathrm{R}}_{2}$${\mathrm{Fe}}_{17}$ single crystals have been analyzed quantitatively in a wide temperature range, using a two-sublattice approximation for the magnetic structure and taking into account isotropic exchange and single-ion crystal-field interactions. The 3d sublattice behavior has been described phenomenologically, from the study of the experimental magnetization results in a ${\mathrm{Y}}_{2}$${\mathrm{Fe}}_{17}$ single crystal. The parameters ${\mathrm{A}}_{2}^{0}$, ${\mathrm{A}}_{4}^{0}$, ${\mathrm{A}}_{6}^{0}$, ${\mathrm{A}}_{6}^{6}$, describing the crystal-field interaction in the different ${\mathrm{R}}_{2}$${\mathrm{Fe}}_{17}$ compounds (R=Er,nDy,nHo) have been determined. The calculated magnetic behavior shows good agreement with experimental magnetization results in the temperature range 4.2 to 300 K, demonstrating the reliability of the determined parameters.

Magnetic susceptibility of RNi5 single crystals (R  Gd, Tb, Dy) was studied under uniform and uniaxial pressures at temperatures above TC. The uniform pressure derivatives of the paramagnetic Curie temperature ϑ and the crystalline electric field parameter B20 appear to be small. On the other hand, ϑ and B20 parameters display a large sensitivity to the uniaxial pressure due to related changes of c/a ratio. Ab initio electronic structure calculation was performed for GdNi5 to evaluate the volume derivative of TC.

We present heat capacity, AC-susceptibility and DC-susceptibility measurements of UNi2Al3 single crystal. Our results are consistent with the characterisation of UNi2Al3 as heavy-fermion superconductor with superconducting transition at Tc ≈ 1 K, which shows antiferromagnetic ordering below TN ≈ 5 K.

We have studied non-Fermi liquid properties of the tetragonal diluted uranium alloys Th1−xUxRu2Si2 (x ≤ 0.07), by means of thermal expansion measurements in the temperature range 0.5–100 K. As the temperature is lowered below about 10 K, the volume effect αv(T)/T (=(αc + 2αa)/T) is found to exhibit the tendency to diverge logarithmically, similar to other quantities of the system: C/T ∼ − ln T, ϱ ∼ −ln T (or T12). Interestingly, the sign of the anomaly in αv(T) is negative, opposite to the usual Kondo shrink behavior. As a possible interpretation, we discuss the two-channel Kondo model, proposing c-f hybridization effects dominated by the virtual f2-f3 charge fluctuations.

A vertical floating zone method was successfully use to growth single crystals of heavy fermion systems UPt3 and UNi2Al3. Metallurgical aspects of the crystal preparation are discussed. Superconducting and magnetic properties of the crystals were studied by means of electrical resistivity and heat capacity measurements down to 350 mK. In the best case, the resistivity of UPt3 exhibits a transition to superconductivity between 530 mK and 560 mK and a sharp double transition in heat-capacity data. The heat capacity data of UNi2Al3 show sharp peaks corresponding to superconducting or to magnetic transition below 1.1 K and 5 K.

We have studied the magnetization of amorphous Co-Dy-B and Fe-Dy-B alloys at 1.5 K under very high fields up to 35 T. Above a critical field the antiferromagnetic coupling breaks as indicated by the strong increase in the magnetization. This is explained by a model. The analysis of this behavior enables us to obtain some important parameters of fundamental interest. (C) 1996 American Institute of Physics.

Magnetization studies on single-crystalline NdNi5 in external fields up to 35 T are reported. NdNi5 is a ferromagnet with a TC of 7.2 K and the easy magnetic direction is along the a direction. The spontaneous magnetic moment is 2.1 μB/f.u. Along the c-axis, the magnetization amounts to 1.65μB/f.u. at 35 T. The magnetization process is analyzed within the crystalline-electric-field approach in combination with exchange interactions, taking into account the contribution of the Ni sublattice. The studies confirm that the charge-formed ground state of the f3 (Nd3+) subsystem is the state Γ8 with a dominant | ± 52〉 contribution. The full magnetization curves, up to 300 T, have been calculated. The magnetization curve along the c-axis proceeds to saturation with a metamagnetic-like transition at 150 T.

High-field magnetization on two single-crystalline samples from different batches of TmNi5 has been measured along the crystallographic a, b and c directions up to 38 T at 1.5 K. A small high-field susceptibility χHF = 6.3 × 10−3μB/T f.u. was observed along the easy c-axis. The magnetization measured along both a- and b-axis shows hysteresis and a magnetic transition between 5 and 15 T. Specific heat has been measured from 1.5 to 160 K. A λ-type peak found at about 3.7 K originates from the magnetic system.

We present zero-field muon-spin-relaxation data on the ferromagnetic fluctuations near the Curie temperature of the intermetallic GdNi5, which is a Heisenberg magnet with strong dipolar interaction. Our data show that the critical longitudinal ~along the wave vector qO spin fluctuations above and below the Curie temperature are similar. They are an experimental proof of this similarity. This result is explained using the dynamical scaling theory of Halperin and Hohenberg. Although the transition from the paramagnetic to the ordered state of a simple ferromagnet is an archetypical second-order phase transition, the dramatic effect of the dipolar interaction on the nature of the critical paramagnetic spin fluctuations has been fully understood only recently. An almost quantitative agreement has been achieved between the experimental data from magnetization, 1 neutron, 2 and local probe 3,4 techniques and mode coupling theory. 5 In contrasts below the Curie temperature TC the experimental data are scarce 6,7 and a complete theory is still lacking. 8 This report presents a detailed study on crystals of the spin dynamics for a dipolar Heisenberg ferromagnet by a local

Large single crystals of the ternary intermetallic boride UNi411B have been grown by the “tri-arc” Czochralski technique and characterised by means of optical microscopy, X-ray diffraction, and electron-probe microanalysis. Parameters of the crystal growth, such as seed rotation and translation as well as crucible rotation, have been optimised. The best result has been obtained without any crucible rotation, 5 mm/h seed translation and 12 rpm seed rotation. The distribution of boron has been carefully studied. Electron-probe microanalysis revealed the presence of small particles rich in boron. Low-temperature properties of the single crystals have been characterised by means of resistivity, magnetic susceptibility and heat-capacity measurements.

Specific-heat measurements have been performed on single-crystalline PrNi5 from 1.3 to 250 K, in order to evaluate the contribution of the Pr subsystem. PrNi5 does not order magnetically down to the lowest temperatures as crystalline-electric-field (CEF) interactions, producing the non-magnetic singlet ground state Γ4, dominate the exchange interactions. Analysis of the specific heat unambiguously establishes the position of the two lowest excited levels at 33.7 K (Γ1) and 45.7 K (Γ6) which levels cannot be observed in inelastic-neutron-scattering experiments. A set of CEF parameters of the Pr3+ ion in the f2 configuration has been evaluated that gives the best account for all known experimental results of this compound.

The linear coefficients of thermal expansion, α(T), of the Kondo insulator CeRhSb and its non-f-electron analog LaRhSb have been measured on polycrystalline samples in the temperature range 1.5–200 K. After subtracting the phonon contribution (θD = 260 K), the f-electron contribution to the thermal expansion, αm(T), shows two distinct features, a broad maximum is centered at 125 K, while a large shoulder appears below 40 K. In a plot of αm/T versus T, a maximum appears at the temperature where the energy gap opens, Tg = 10 K. For T < Tg, αm(T) follows an aT + bT2 law, which is compatible with a description of the energy gap vanishing on lines at the Fermi surface.