M. Diviš

Heavy fermion behavior of U2T2X compounds

Magnetic and specific-heat studies of U[sub 2][ital T][sub 2][ital X] compounds show a frequent occurrence of the [gamma] enhancement in conjunction with the onset of antiferromagnetic ordering. The largest value of 830 mJ/mol K[sup 2] was observed in U[sub 2]Pt[sub 2]In, which is nonmagnetic down to 1.2 K. Variations of electronic structure are documented by optimized relativistic LCAO calculation.Magnetic and specific‐heat studies of U2T2X compounds show a frequent occurrence of the γ enhancement in conjunction with the onset of antiferromagnetic ordering. The largest value of 830 mJ/mol K2 was observed in U2Pt2In, which is nonmagnetic down to 1.2 K. Variations of electronic structure are documented by optimized relativistic LCAO calculation.

Magnetism in RENiAl compounds

Results of magnetic, resistivity and specific heat measurements of RENiAl compounds are presented. Except for CeNiAl, all the compounds with the unfilled f‐shell rare earths exhibit magnetic ordering at low temperatures. In the majority of cases, we observe one or two additional magnetic phase transitions below the ordering temperature. In RENiAl antiferromagnets, metamagnetic transitions are observed in moderate magnetic fields. Magnetization measurements performed on oriented powders reveal a strong magnetocrystalline anisotropy (except for GdNiAl and CeNiAl) which originates in crystal field interaction. The energy spectra of the RE 4f states were obtained from the analysis of the Schottky anomalies found in the specific heat data. This analysis also revealed indications of strong magnetic correlations in the paramagnetic state.

Crystal field in rare earth intermetallics with CsCl structure

Abstract Electronic structure of rare earth intermetallics REX (RE  Y, Er; X  Rh, Cu, Ag, Zn, and Mg) was calculated using the full potential LAPW method in the LDA (LSDA) approximation. The crystal field (CF) splittings of RE 3+ energy levels were obtained from the aspherical components of the self-consistent potential from the region inside the RE muffin-tin sphere as well as from the interstitial region. We show that the calculated CF parameters account for the experimentally observed trend in sign and even values of CF parameter A 4 0 〈 r 4 〉. As the charge density of the whole crystal contributes to CF in general, we provide the discussion of contributions to CF from the different regions of REX crystals.

U Ternaries with ZrNiAl Structure - Lattice Properties.

The bonding properties of UTX compounds having the hexagonal ZrNiAl-type structure display a pronounced anisotropy. The compressibility and thermal expansion reach values several times higher for the basal plane than along the c-axis. This situation also occurs for the Th-containing counterparts, whereas it is absent in isostructural materials based on rare earths. This phenomenon can be attributed to the participation of the delocalized 5f states in the bonding, leading to compression of the 5f charge towards the basal plane. This scenario has been investigated theoretically by ab-initio band structure calculations performed for URhAl.

Electronic structure and hybridization in U2T2In (T = Co, Ni, Pd) intermetallics

Abstract Ab initio electronic structure calculations of U 2 T 2 In ( T = Co , Ni , Pd ) intermetallic compounds were performed using an optimized LCAO method based on the LDA approximation. The particular electronic structure and related properties of U 2 T 2 In originate from the interplay between the band filling of the free electron background (s-, p- and uranium d-electrons), transition metal bonding bands and covalency (hybridization) between bonding predominantly d-states of T atoms and antibonding predominantly f-states of U atoms. The observed experimental trends in the term γ T and magnetic properties of U 2 T 2 In are qualitatively consistent with the results of our approach.

Crystal field phenomena in rare earth cuprates

Abstract We present some results pertaining to the crystal field (CF) interactions in high T c rare earth (RE) cuprates and related layered compounds and manifestations of their impact on magnetic properties. We show that the widely disputed specific-heat and susceptibility data in PrBa 2 Cu 3 O 7 can be interpreted consistently in terms of the standard CF theory for Pr 3+ based on the CF parameters extracted from the inelastic neutron scattering spectra via the superposition model. The CF-induced electric quadrupoles are shown to lead to thermal expansion anomalies in Sm 2 CuO 4 and REBa 2 Cu 3 O 7 compounds. We examine general conditions for an Ising-like behaviour of the RE subsystem. We conclude that such a behaviour may possibly occur in cuprates containing Tb, Dy and Ho owing to the special nature of low-lying 4f states imprinted by the CF interaction.

Magnetism of PrAl2 nanoparticle investigated with a quantum simulation model

For many years, micromagnetism and Monte Carlo simulation have served as the two main tools for studying the magnetic structures and physical properties of nanomagnets. However, the two approaches are based on classical physics, and thus lack the flexibility to deal with complex nanosystems, such as those of very tiny size or consisting of ions of different elements. To overcome the difficulty, a quantum simulation model has been proposed and a new computational algorithm developed in the present work. Both have been successfully applied to an assumed PrAl₂ nanoparticle to study its magnetic behavior in external magnetic fields exerted along the crystal axes. The theoretical results obtained with the model and the new algorithm are reasonable physically and exhibit strong finite-size effects. The model can be generalized to study the magnetic configurations and physical properties of more complicated nanosystems, such as nanowires, nanotubes, etc.

Influence of the magnetic anisotropy on the relaxation behaviour in DyCu2 and ErCu2

Abstract The orthorhombic intermetallic compounds DyCu 2 and ErCu 2 were measured with 161 Dy and 166 Er Mossbauer spectroscopy, respectively. DyCu 2 , which has a weak magnetic anisotropy parallel to the a -axis, shows no relaxation traject above T N . In contrast, ErCu 2 has a strong magnetic anisotropy parallel to the b -axis and shows a long relaxation traject above T N = 11.5 up to 45 K. A very good correspondence is found between the results of ErCu 2 obtained by inelastic neutron scattering and by 166 Er Mossbauer spectroscopy.

Magnetic properties of RCuAl and RNiAl compounds

Abstract Results of structure, susceptibility and specific heat studies of RCuAl and RNiAl compounds are presented. Most of the compounds with a partially filled f-shell exhibit magnetic ordering at low temperatures. The ordering temperatures and paramagnetic Curie temperatures are roughly proportional to de Gennes factor.

Electronic structure of U2T2X intermetallic compounds

Abstract Ab initio electronic-structure calculations for the normal metallic state of U 2 T 2 X (T  Co, Ni, Rh, Pd, Ir, Pt; X  In, Sn) compounds were performed using a fully relativistic optimized LCAO method based on the local density approximation. The particular electronic structure and related properties originate from the interplay between the band filling of T atom d-states and hybridization between T atom d-states and U atom f-states.