A. Czopnik

Low-temperature thermal properties of yttrium and lutetium dodecaborides

The heat capacity (Cp) and dilatation (?) of YB12 and LuB12 are studied. Cp of the zone-melted YB12 tricrystal is measured in the range 2.5?70?K, of the zone-melted LuB12 single crystal in the range 0.6?70?K, and of the LuB12 powder sample in the range 4.3?300?K; ? of the zone-melted YB12 tricrystal and LuB12 single crystals is measured in the range 5?200?K. At low temperatures a negative thermal expansion (NTE) is revealed for both compounds: for YB12 at 50?70?K, for LuB12 at 10?20?K and 60?130?K. Their high-temperature NTE is a consequence of nearly non-interacting freely oscillating metal ions (Einstein oscillators) in cavities of a simple cubic rigid Debye lattice formed by B12 cage units. The Einstein temperatures are ~254 and ~164?K, and the Debye temperatures are ~1040?K and ~1190?K for YB12 and LuB12 respectively. The LuB12 low-temperature NTE is connected with an induced low-energy defect mode. The YB12 superconducting transition has not been detected up to 2.5?K.

Magnetic and structural transitions in TmGa3

Abstract We have established for TmGa 3 the occurrence of two close lying first-order transitions. The first transition at T Q = 4.29 K drives the compound to a distorted phase and the second one at T N = 4.26 K to an antiferromagnetic state. They are pushed apart markedly by an applied magnetic field. In the whole temperature range of the ordering we have observed a first-order field-induced metamagnetic transition along the 〈100〉 direction. The temperature variation of the reciprocal susceptibility gives magnetic Γ (5) 5 as the ground state. It is well known that the Γ 5 ground state of a Tm 3+ ion leads to a strong first-order structural transition in TmCd and TmZn intermetallics. Therefore we may assume that the structural transition in TmGa 3 has the same origin as in the compounds mentioned above. This transition is driven by quadrupolar pair interactions. The lattice follows the quadrupoles and distorts in such a way as to minimize the Jahn-Teller coupling energy.

Neutron diffraction on a UGa3 single crystal

Abstract The magnetic structure of antiferromagnetic UGa3 (TN≈64 K) has been examined by neutron diffraction measurements on a single crystal. The ordered magnetic moment is 0.74(8)μB per U atom at 5 K. From measurements with an applied magnetic field we suggest that the moments are along the [1 1 1] direction. In the vicinity of 40 K the mosaic of the crystal changes significantly. This coincides with the anomaly in the magnetic susceptibility observed at the same temperature, indicating a possible crystallographic distortion or a reorientation of the magnetic moments.

Conduction-electron-mediated exchange coupling in heavy rare earth metal compounds RM and RM3

Abstract The effect of pressure on the magnetic susceptibility of rare earth compounds GdM (MCu, Ag, Mg) and RIn 3 (RGd, Tb, Dy) has been investigated. The experimental data and results of ab initio calculations of the volume derivatives of the band structure and the exchange parameters for the corresponding series of compounds have been used to analayze the nature of the f-f interactions.

Temperature- and field-induced transitions in NdIn3

Abstract The cubic (AuCu3 type structure) compound NdIn3 has been investigated by means of specific heat, thermal expansion and high-field magnetization experiments. It undergoes at 5.90 K a second-order transition to an antiferromagnetic state. In the ordered range we have discovered two first-order transitions at T(1)c = 4.61 K and T(2)c = 5.13 K. At low temperatures in comparison to TN we have observed two sharp, first-order field-induced metamagnetic transitions in the 〈001〉 direction. The first of these is the transition to an intermediate phase I with a magnetization equal to half of the saturation value, and the second one to the paramagnetic state P. At high temperatures the AF-I and I-P transitions are of second order. The changeover from the second- to the first order occurs at the tricritical point for the I-P transition and at the multicritical point for the AF-I one. These critical points are near 4.0 K. In the intermediate phase I a perpendicular spin arrangement probably occurs.

Low temperature heat capacity and magnetic susceptibility of Ti3SiC2

In this paper, we report on the heat capacity and magnetic susceptibilities of bulk Ti3SiC2 samples in the 3–250-K temperature range. At 13.6 K, a nonmagnetic sharp anomaly of unknown origin, which disappeared when the sample was heated and quenched in water from 1400 °C, is observed. Curve fitting the cp data up to 100 K clearly shows that only four atoms—most likely one Si and three Ti atoms—of the six in a formula unit contribute to cp at the lowest temperatures. This reduces the Debye temperature θD calculated from over 700 K to ≈575 K. To obtain good agreement between experimental and calculated cp values in the 14 130 K, two other optical modes—the average of two other Raman modes observed at higher wave numbers—are required to enhance the fits to the experimental results. In the absence of the anomaly, θD rise...

de Haas-van Alphen effect in ScGa3, LuGa3 and YIn3

Abstract The angular dependencies of the de Haas-van Alphen (dHvA) frequencies and the corresponding cyclotron masses are determined for ScGa3, LuGa3, and YIn3 in the planes {100} and {110}. The dHvA frequency branches for all three compounds are in the range from 2.3 × 106 Oe to 105 × 106 Oe. For all of them cyclotron masses are light; their values are between 0.2m0 and 0.8m0.

The Fermi surface of ErGa3

The Fermi surface geometry and cyclotron masses of the antiferromagnet ErGa3 in a magnetic-field-induced paramagnetic phase are determined by using the de Haas-van Alphen effect method. The results are analysed on the basis of ab initio band-structure calculations and compared to corresponding results for the isostructural compounds TmGa3 and LuGa3.

Specific heat, susceptibility, magnetotransport and thermoelectric power of the Kondo alloys (Ce1-xLax)Cu5In

The influence of substituting Ce with La in the Kondo compound CeCu5In has been investigated using x-ray diffraction, specific heat (Cp), electrical resistivity (?(T)), magnetoresistivity?(MR) and thermoelectric power?(TEP) measurements. Cp of CeCu5In and the (Ce1?xLax)Cu5In alloys shows enhanced values at low temperatures. Between?10 and 20?K the equation Cp/T = ?conv+?T2 fits the data for all alloys with ?conv scaling linearly with Ce concentration. Below 10?K a pronounced upturn in Cp values occurs. Susceptibility data above 100?K follow the Curie?Weiss relation and give effective moment ?eff values in fair agreement with that of a Ce3+-ion. The ?(T) studies illustrate the evolution from Kondo lattice to single-ion Kondo behaviour with increase in La content in the (Ce1?xLax)Cu5In alloy series. MR measurements on Ce dilute alloys are interpreted within the single-ion Bethe ansatz description and values of the Kondo temperature TK are calculated. A compressible Kondo lattice model has been used to describe the decrease in TK and in Tm? (the temperature at which a maximum in ?(T) occurs for the coherent dense Kondo alloys) with decrease in Ce concentration for these alloys. The TEP is positive and shows a maximum at approximately 45?K for several investigated (Ce1?xLax)Cu5In alloys.

Itinerant f-electron antiferromagnetism in UGa3

Single crystals of the antiferromagnetic compound UGa3 were studied by means of pressure dependent electrical resistivity measurements. The Neel temperature was found to decrease with rising pressure at the rate of −1.4 K/bar. A rapid reduction of TN was also observed in the electrical resistivity studies of the pseudobinary system U(Ga1−xGex)3, where the substitution for Ga of a smaller atom was equivalent to a positive chemical pressure. The results corroborate an itinerant- electron nature of the magnetism in UGa3 which was suggested before on the basis of the peculiar magnetic and thermodynamic properties of this compound.