Physics of Polymorphic Transitions in CeRuSn

We report a detailed study of the polymorphic transitions in ternary stannide CeRuSn on high quality single crystals through a combination of X-ray diffraction experiments conducted at 300, 275 and 120 K, and measurements of the thermal expansion, magnetization, and resistivity, along main crystallographic axes. In addition, the transition was followed as a function of pressure up to 0.8 GPa. The present X-ray diffraction data show that the room temperature polymorph consists of the lattice doubled along the c axis with respect to the CeCoAl-type structure consistent with previous reports. Upon cooling, the compound undergoes two successive transitions, first to a quintuple (290 K) and than to a triple CeCoAl superstructure at 225 K. The transitions are accompanied by a tremendous volume change due to a strong shrinking of the lattice along the c axis, which is clearly observed in thermal expansion. We advance arguments that the volume collapse originates from an increasing number of crystallographically inequivalent Ce sites and the change of ratio between the short and long Ce-Ru bonds. The observed properties of the polymorphic transition in CeRuSn are reminiscent of the transition in elementary Cerium, suggesting that similar physics, i.e., a Kondo influenced transition and strong lattice vibrations might be the driving forces

Characterization of U-based thin films: the UFe₂₊ₓ case

We have characterized UFe₂₊ₓ films prepared by sputter deposition onto fused silica (SiO₂) and Si(111) substrates with the film thickness ranging from 75 nm to 900 nm. The X-ray diffraction results showed an amorphous character of the deposited material. Some of the films showed in addition a pattern of highly textured cubic Laves phase. Rutherford Backscattering Spectroscopy with 2 MeV He⁺ ions has been used to determine the composition, thickness and concentration depth profile of the films. A large ageing affect was observed within 1 month after that the films were exposed to air. Magnetic measurements revealed TC increasing with relative Fe concentration and reaching approx. 450 K in UFe₃.₀

Spontaneous Magnetostriction of Lu2Fe17−xSixLu_2Fe_{17-x}Si_x

Thermal expansion of $Lu_2$ $Fe_{17-x}Si_x$ solid solutions was measured by X-ray powder diffraction. The magnetic ordering in all compounds within the homogeneity range (x≤3. 4) is accompanied by a large spontaneous volume magnetostriction distributed anisotropically over the principal axes of the hexagonal crystal structure. The volume effect ω_s in the ground state reaches $14.7×10^{-3}$ in $Lu_2Fe_{17}$ and decreases monotonously to $8.9×10^{-3}$ at x = 3.4 following the reduction of magnetic moment. Despite still large $ω_s$, the Invar behavior observed in $Lu_2Fe_{17}$ changes to a positive thermal expansion for x >1 due to increasing Curie temperature

Specific Heat Study of PrNi 4

Here we present the results of pilot polycrystalline study of $PrNi_4Si$. The X-ray study did not confirm the expected $CaCu_5$-type structure. Instead of this, the orthorhombic structure with the space group Cmmm was found. The zero-field specific heat was measured in the temperature range 2-300 K. The data were analyzed using the sum of the phonon, electronic, and magnetic contributions to specific heat, respectively. The magnetic part of the specific heat can be well described using the Schottky formula for the 9 crystal-field singlet levels of the pz3 H4 ground-state multiplet of the $Pr^{3+}$ ion

Specific Heat Study of PrNi4SiPrNi_4Si

Here we present the results of pilot polycrystalline study of $PrNi_4Si$. The X-ray study did not confirm the expected $CaCu_5$-type structure. Instead of this, the orthorhombic structure with the space group Cmmm was found. The zero-field specific heat was measured in the temperature range 2-300 K. The data were analyzed using the sum of the phonon, electronic, and magnetic contributions to specific heat, respectively. The magnetic part of the specific heat can be well described using the Schottky formula for the 9 crystal-field singlet levels of the pz3 H4 ground-state multiplet of the $Pr^{3+}$ ion

Structural Phase Transition in CeCuAl3CeCuAl_{3} Single Crystal

The high temperature properties of $CeCuAl_{3}$ single crystal were investigated by differential scanning calorimetry and high-temperature x-ray diffraction. The structural phase transition takes place around 300 °C. The phase transition changes the structural parameters only, the tetragonal $BaNiSn_{3}$-type structure is preserved. The significant changes of lattice parameters and especially atomic fraction coordinates with this transition are discussed with respect to the number of heating/cooling cycles and stability in time. Magnetic properties of as-cast and annealed sample are shown for comparison

Magnetic Anisotropy of Lu2Co17−xSixLu_2Co_{17-x}Si_x Single Crystals

Magnetic anisotropy of $Lu_2Co_{17-x}Si_x$ single crystals grown by the Czochralski method was investigated. The homogeneity range of Si substitution for Co extends up to x = 3.4 in $Lu_2Co_{17-x}Si_x$ solid solutions. The unit cell volume, Curie temperature, and spontaneous magnetic moment decrease monotonously with increasing Si content. $Lu_2Co_{17}$ has the easy-plane type of magnetic anisotropy in the ground state, which changes into the easy-axis type by two spin-reorientation transitions of the second-order, the easy-plane-easy-cone at $T_{SR1}$~680 K and the easy-cone - easy-axis at $T_{SR2}$~730 K. Upon Si substitution, the observed spin-reorientations shift towards the lower temperatures for $Lu_2Co_{17-x}Si_x$ $(T_{SR1}$~75 K and $T_{SR2}$~130 K in $Lu_2Co_{16}Si$) and vanish for compounds with 1<x≤3.4, which have the uniaxial type of magnetic anisotropy in the whole temperature range of magnetic order

Lattice Heat Capacity in RTAl (R = Y, Lu; T = Ni, Cu, Pd) Compounds

We present analysis of the specific heat of the RTAl (R = Y, Lu; T = Cu, Ni, Pd) compounds. We focus on the lattice contribution and analyze the dependence of all the characteristic parameters in the Debye and Einstein models on the atomic masses and interatomic distances