J. Prchal

Nature of the magnetic ground state in the mixed valence compound CeRuSn: a?single-crystal study

We report on detailed low-temperature measurements of the magnetization, the specific heat and the electrical resistivity on high-quality CeRuSn single crystals. The compound orders antiferromagnetically at T(N) = 2.8 K with the Ce(3+) ions locked within the a-c plane of the monoclinic structure. Magnetization shows that below T(N) CeRuSn undergoes a metamagnetic transition when applying a magnetic field of 1.5 and 0.8 T along the a- and c-axis, respectively. This transition manifests in a tremendous negative jump of ~25% in the magnetoresistance. The value of the saturated magnetization along the easy magnetization direction (c-axis) and the magnetic entropy above T(N) derived from specific heat data correspond to the scenario of only one third of the Ce ions in the compound being trivalent and carrying a stable Ce(3+) magnetic moment, whereas the other two thirds of the Ce ions are in a nonmagnetic tetravalent and/or mixed valence state. This is consistent with the low-temperature CeRuSn crystal structure i.e., a superstructure consisting of three unit cells of the CeCoAl type piled up along the c-axis, and in which the Ce(3+) ions are characterized by large distances from the Ru ligands while the Ce-Ru distances of the other Ce ions are much shorter causing a strong 4f-ligand hybridization and hence leading to tetravalent and/or mixed valence Ce ions.

Effects of high pressure on the magnetism of ErCo2

This paper presents the results of a high pressure study on the ferrimagnetic compound ErCo2, which exhibits at ambient pressure magnetic ordering below TC = 33 K, where the localized Er magnetic moments order ferromagnetically, and the itinerant moments in the Co sublattice, align antiparallel to the Er moments. In the paramagnetic range, clustering of the Co moments is observed below Tf ∼ 100 K for which the term “parimagnetism” has been proposed. In contrast to the pronounced peak in the AC susceptibility data at TC only a tiny “bump” shows up at Tf. The decrease of both TC and Tf with applied hydrostatic pressure has been observed, the first one being in agreement with previously published data. At higher pressures, an asymmetry in the TC-related AC susceptibility peak has been observed owing to a decoupling of the magnetic ordering phenomena in the Er and Co sublattices. Compared to earlier published results, our magnetization measurements at higher pressures above PC reveal a small but clearly obser...

Crystal and magnetic structures in the Tb(Pd,Ni)Al series

We report on the magnetic structures in the TbPd 1-x Ni x Al compounds as determined by powder neutron diffraction. The development of magnetic structures in the Tb(Pd, Ni)Al series is relatively simple. All the compounds show the existence of two magnetic phases with almost unchanged Neel temperature T N ≃ 44 K and an additional magnetic phase transition temperature T 1 ≃ 23 K. The arrangement of the Tb moments between T N and T 1 is identical for all the concentrations and is characterized by a (1 2, 0, 1 2) propagation vector with one-third of Tb moments frustrated to nearly zero. Certain concentration development occurs only below T 1 . Magnetic moments that are frustrated between T N and T 1 change their propagation below T 1 to commensurate (1 2, - 1 2, 1 2) or incommensurate (1 2,-τ -, 1 2), depending on the Ni concentration. The magnetic moments stay parallel to the hexagonal c axis for all concentrations and temperatures.

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.

Magnetism and Structural Behavior of CeRuSn Single Crystal

We have synthesized CeRuSn single crystals and performed measurements of electrical resistivity and specific heat. At high temperatures, abrupt transitions were observed at 290 and 225 K in electrical resistivity during cooling. Both transitions are connected with a large temperature hysteresis. Low temperature properties are dominated by an antiferromagnetic transition at 2.9 K, which involves only half of cerium ions, leaving the rest of them non-magnetic. A significant magnetocrystalline anizotropy was revealed by application of external magnetic field.

Structural and magnetic study of SmTAl single crystals (T=Pd and Ni)

Some of the RTX (R – rare earth, T – transition metal, X – p-metal element) including SmNiAl and SmPdAl, compounds crystallizing in the hexagonal ZrNiAl-type of structure exhibit a discontinuity in the temperature or composition dependence of the lattice parameters (a and c). This phenomenon is connected with some “forbidden” c/a ratio values. Single crystals of SmNiAl and SmPdAl have been studied and found to undergo a second order structure phase transition in the vicinity of 500 K, characterized by a change of the temperature dependence of the c/a ratio. The transition is seen also in the change of the temperature dependence of the magnetic susceptibility near to 500 K. The second order type of the transition induces appearance of c/a falling into the forbidden range of values. The enhanced thermal movement at high temperatures causes possibility of the forbidden values. The low temperature specific heat, resistivity and magnetization data point to antiferromagnetism in SmPdAl and SmNiAl with TN = 15.3...

High pressure resistivity of UPd3

Electrical resistivity of UPd3, the only known binary U-based intermetallic with localized 5f states, was studied under high pressures up to 10 GPa, testing a possible incipient delocalization due to the lattice compression. The data obtained revealed no tendency to any delocalization. The shoulder related to crystal-electric field effects between 10 and 15 K remains visible, being only shifted slightly towards higher temperatures with the increase in pressure.

Field-induced magnetic ordering in ErNi1-xCuxAl

The RNi1-xCuxAl pseudoternaries belong to group of RTX intermetallic compounds crystallizing in the hexagonal ZrNiAl type of structure. In the critical region of the substitution parameter x ~ 0.8 there was found a loss of a long-range magnetic order at the lowest studied temperatures for series with R = Tb, Dy, Er. As an explanation for this effect a competition of different ordering mechanisms for either RNiAl or RCuAl compounds was proposed. Nevertheless, the magnetization curves of the ErNi0.2Cu0.8Al compound (within the critical concentration region) showed behaviour close to the parent ErCuAl, which was confirmed as a ferromagnet. Neutron diffraction on ErNi0.2Cu0.8Al compound with applied magnetic field signifies appearing of the ferromagnetic order at the lowest applied magnetic field of 0.1 T. The magnitude of the ordered magnetic moment increases with increasing magnetic field in agreement with the magnetization curve, confirming tendency to ferromagnetic ordering or short-range magnetic order of ferromagnetic character in this critical region.

Lattice distortion in TmCo2: A poly- and single-crystal study

Abstract Within the RCo2 family of compounds, a structural distortion linked with the onset of magnetic ordering around the critical temperature can be observed. One of the less explored RCo2 compounds is TmCo2 probably due to its low Curie temperature. Exceptionally this compound, given its position at the end of the ferrimagnetic series, shows discrepancies in the ordering of the Co sub-lattice because of a weak Weiss molecular field. In this paper we focus on the structural distortion in TmCo2, which appears together with the magnetic ordering around the critical temperature of T C ∼ 3.6 K. Poly-crystals as well as single-crystals of TmCo2 were used in our experiments. For both kinds of samples we observed the same type of the rhombohedral distortion along the [111] direction from the cubic Fd 3 ¯ m to R 3 ¯ m space group. The relation between observed magnetic and structural properties in this compound is discussed.

Antiferromagnetism and phase transitions in noncentrosymmetric UIrSi3

Magnetization and specific heat measurements on a UIrSi3 single crystal reveal Ising-like antiferromagnetism below T