Anisotropic p−ƒ mixing mechanism explaining anomalous magnetic properties in Ce monopnictides

Anomalously small crystalline field splitting in the paramagnetic region and extremely strong magnetic anisotropy in the ordered phases in CeSb and CeBi are explained based on the anisotropic mixing mechanism between the 4? states and the valence bands. In the paramagnetic region, the mixing gives the effective crystalline field splitting which is estimated to cancel the splitting of the point charge model in good agreement with experiment. The anisotropy energy of CeSb calculated by using the realistic valence bands is consistent with the strong anisotropy observed experimentally.     

Magnetic fluctuations of filled skutterudites emerging in the transition region between singlet and triplet states

In order to clarify magnetic properties of filled skutterudites, we analyze the Anderson model including seven f orbitals hybridized with an au conduction band using a numerical technique. For n=2 corresponding to Pr-based filled skutterudites, where n is the local f-electron number, even if the ground state is a singlet, there remain significant magnetic fluctuations from a triplet state with a small excitation energy. This result can be understood by the fact that f-electron states are clearly distinguished as itinerant and localized ones in the filled skutterudite structure. This picture also explains the complex results for f-electron magnetic susceptibility and entropy for n=1-13.     

Zeeman effect on magnetic susceptibility in singlet ground state PrNi5

The Zeeman effect on the crystal electric field (CEF) magnetic susceptibility in 4f-electron singlet ground state (SGS) systems is studied analytically in the framework of the molecular-field model and experimentally by measuring the magnetic susceptibility of SGS compound PrNi₅. The most striking result of the analysis is the shift of the zero-field magnetic susceptibility maximum to lower temperatures in magnetic field. This thoroughly CEF effect is a direct consequence of the convergence of the SGS and the low lying Zeeman branch of the first excited state in an applied magnetic field. The observed shift of the susceptibility maximum from 14 K to 9 K in polycrystalline PrNi₅ by applying a magnetic field of 9T confirms the foregone conclusion.     

Magnetic properties of CeSb and DySb from μSR

ZFSR experiments on CeSb and DySb reveal fast spin dynamics even in their magnetically ordered states below 16.2 and 9.5 K, respectively. Above these first order transitions both pnictides exhibit strong frequency shifts in TF pointing to some magnetic precursors. The signals below T _N show spontaneous rotating contributions. For CeSb several commensurately modulated antiferromagnetic phases containing paramagnetic sheets are confirmed. For DySb our data favor a CoO type structure in contrast to the MnO structure proposed from neutron diffraction.Part of this work was funded by the German Federal Minister for Research and Technology (BMFT) under contracts No 03-LI3-BRA and 03-KA2-TUM-4.     

Hybridization gap in heavy fermion compounds

We report the results of optical studies of new heavy fermion compounds YbFe(4)Sb(12) and CeRu(4)Sb(12). We show that these compounds, as well as several other heavy fermion materials with a nonmagnetic ground state, obey a universal scaling relationship between the quasiparticle effective mass m(*) and the magnitude of the energy gap Delta in the excitation spectrum. This result is in accord with the picture of hybridization of localized f-electron and free carrier states.     

Magnetic moments contribution to the specific heat and susceptibility of heavy fermion system

In non-magnetic heavy fermion systems, valence fluctuations prevent formation of long-range magnetic correlations. The RKKY exchange fields fluctuate due to f-electron transfers to the conduction band. To simulate these processes, we use the Ising-type model with fluctuating fields. The linear temperature dependence of the specific heat and temperature independence of susceptibility suggest that the f-electron contribution to these quantities can be considered as complementary to the one originating from Kondo resonance.     

Physics of the f-electron intermetallics

Properties of lanthanide and actinide intermetallics are extremely interesting both for applications and fundamental research. The impetus to start fundamental research on f-electron materials doubtlessly was the determination of the ferromagnetic properties of UH₃ and UD₃ by the research group of the Institute of Low Temperature and Structure Research in Wroclaw and detection of the mixed valence state in samarium monochalcogenides at A. F. Ioffe Physicotechnical Institute in Leningrad (at that time). Since then, the phenomena of the mixed valence, heavy-fermion, state as well as complicated magnetic structures have been under intensive investigation in numerous laboratories all over the world. As examples, the exotic magnetic structures of CeSb and UNi₄B are described. Then the problems of the heavy-fermion state existing in UBe₁₃ and UCu_4+x Al_8−x are presented. Next, the non-Fermi-liquid behavior appearing due to magnetic instability is discussed. Finally, some perspective for further research is proposed. Fiz. Tverd. Tela (St. Petersburg) 41, 813–817 (May 1999) Published in English in the original Russian journal. Reproduced here with stylistic changes by the Translation Editor.     

重Fermi子体系的自发磁矩和反常比热

本文提出重Fermi子体系是一种局域的f电子可以变化的Kondo体系.理论得到在特定温区可以产生自发磁矩,且由f带离Fermi面的距离之不同而存在不同类型的自发磁矩效应.理论并给出由于局域f电子的变化导致重Fermi子体系比热与温度的反常关系.理论与六种重Fermi子材料比热的实验值符合得相当好. 关键词：     

Pressure effect on the magnetic properties of CeSb

Changes in the magnetic field-temperature phase diagram of CeSb with pressure have been determined up to 6kbar by magnetization measurements on a single crystal. High magnetic fields up to 70 kOe have been applied along a four fold axis of the rock-salt type structure. The features of the phase diagram are not changed by pressure except for a shift towards high temperature. The saturated magnetic moment and the hysteresis of the transition fields are independent of pressure. Variation of exchange energy with volume is deduced from the experimental results. It is shown that the effect of pressure and the magnetic volume anomaly at 0 K are essentially due to the variation of the exchange energy in the ferromagnetic (001) planes.     

Magnetic and transport properties of the magnetic Polaron: application to Eu1-xLaxB6 system

To understand the role of the magnetic polaron in magnetic and transport properties of Eu(1-x)LaxB6, we investigate the low carrier density ferromagnetic Kondo lattice model by using the Monte Carlo methods. We demonstrate that the magnetic-polaronic (MP) state with the insulating nature is realized in the phase-separated region in between the ferromagnetic and antiferromagnetic (AFM) states in the phase diagram. The insulating behaviors of EuB6 just above T(C) and of Eu(1-x)LaxB6 with 0.05相似文献   

Electronic structure of Ce-pnictides

High-resolution x-ray photoemission has been used to study the electronic structure of the Ce-pnictides (CeN, CeP, CeAs and CeSb). This series of isostructural compounds allows us to follow the evolution of the 4f level as the distance between Ce atoms varies. Core level spectra show clearly that the 4f state is localized in all the compounds. In the valence band region, the width of the 4f peak is strongly influenced by the energy overlap with the extended states originating from anion p states. The spectra of CeN reveal the existence of a mixed configuration.     

The f-electron contribution to the elastic property of Ce3S4

The elastic constant, C’, of Ce₃S₄ has been measured as a function of temperature. It is shown that the curve is markedly different from that of La₃S₄. Since the only basic difference between the two compounds is the existence of a f-electron in Ce, we propose a theoretical scheme in which the f-electron plays a crucial role. It is shown that the existence of the f-electron in Ce₃S₄ prevents the band Jahn–Teller type structural transition when the temperature is lowered. The theory is consistent with the experiment and also with the theoretically predicted instability of cubic f-electronelements at zero temperature. Received: 5 October 1999 / Accepted: 11 October 1999 / Published online: 24 March 2000     

Irreversible dynamics of the phase boundary in U(Ru0.96Rh0.04)2Si2 and implications for ordering

We report measurements and analysis of the specific heat and magnetocaloric effect-induced temperature changes at the phase boundary into the single magnetic field-induced phase (phase II) of U(Ru0.96Rh0.04)2Si2, which yield irreversible properties similar to those at the valence transition of Yb(1-x)Y(x)InCu4. To explain these similarities, we propose a bootstrap mechanism by which lattice parameter changes caused by an electric quadrupolar order parameter within phase II become coupled to the 5f-electron hybridization, giving rise to a valence change at the transition.     

Cyclotron resonance in a two-dimensional electron system with self-organized antidots

Experimental data are reported on studying cyclotron resonance in a two-dimensional electron system with an artificial random scattering potential generated by an array of self-organized AlInAs quantum islands formed in the plane of an AlGaAs/GaAs heterojunction. A sharp narrowing of the cyclotron resonance line is observed as the magnetic field increases, which is explained by the specific features of carrier scattering in this potential. The results obtained point to the formation of a strongly correlated electron state in strong magnetic fields at carrier concentrations smaller than the concentration of antidots.     

Fermi surface of CeIn3 above the Néel critical field

We report measurements of the de Haas-van Alphen effect in CeIn(3) in magnetic fields extending to approximately 90 T, well above the Néel critical field of mu(0)H(c) approximately 61 T. The unreconstructed Fermi surface a sheet is observed in the high magnetic field polarized paramagnetic limit, but with its effective mass and Fermi surface volume strongly reduced in size compared to that observed in the low magnetic field paramagnetic regime under pressure. The spheroidal topology of this sheet provides an ideal realization of the transformation from a "large Fermi surface" accommodating f electrons to a "small Fermi surface" when the f-electron moments become polarized.     

Ferrimagnetism in EuFe4Sb12 due to the interplay of f-electron moments and a nearly ferromagnetic host

We combine x-ray magnetic circular dichroism spectroscopy at Fe L2,3 edges, at Eu M4,5 edges, x-ray absorption spectroscopy (XAS) investigation of Eu valence, and local spin density calculations, to show that the filled skutterudite Eu0.95Fe4Sb12 is a ferrimagnet in which the Fe 3d moment and the Eu2+ 4f moment are magnetically ordered with dominant antiferromagnetic coupling. From Eu L3 edge XAS, we find that about 13% of the Eu have a formal valence of 3+. We ascribe the origin of ferrimagnetism at a relatively high transition temperature TC of 85 K in Eu0.95Fe4Sb12 to f-electron interaction with the nearly ferromagnetic [Fe4Sb12]2.2- host lattice.     

Three-dimensional fermi-liquid ground state in the quasi-one-dimensional cuprate PrBa(2)Cu(4)O(8)

The interchain resistivity of PrBa(2)Cu(4)O(8) has been measured in high magnetic fields up to 30 T. Co-herent interchain transport at low temperatures is destroyed by a large magnetic field applied perpendicular to the CuO chains. Comparisons with quasiclassical transport theory provide strong experimental support for a three-dimensional Fermi-liquid ground state in PrBa(2)Cu(4)O(8), despite extreme anisotropy in its electronic properties and the presence of strong electron correlations.     

High pressure electronic properties in the light of inelastic X-ray scattering From magnetic collapse to quantum criticality

The properties of solids are strongly modified at high pressure. Not only their structure is affected as a direct consequence of the compressed lattice, but also their electronic and magnetic properties as pressure alters significantly the electron density and orbital overlap, thus the electronic localization and hybridization. We present here high pressure experiments using resonant inelastic x-ray scattering. RIXS in the high energy range (≥5keV) has appeared as a powerful probe of the electronic properties under extreme conditions. It is chemically and orbitally selective while showing an intrinsic resolving power spectacularly larger than standard spectroscopic probes. Results will be briefly presented in 3d metals and f-electron systems. The behavior of 3d electrons under pressure will be explored in the light of magnetic collapse transitions; We will comment on f-electron delocalization, especially when approaching a Kondo anomaly or a quantum critical point; Pressure dedicated setups are also discussed.     

Evidence for weak itinerant long-range magnetic correlations in UGe2

Positive muon spin relaxation measurements performed on the ferromagnet UGe2 reveal, in addition to the well-known localized 5f-electron density responsible for the bulk magnetic properties, the existence of itinerant quasistatic magnetic correlations. Their critical dynamics is well described by the conventional dipolar Heisenberg model. These correlations involve small magnetic moments.     

Heavy-fermion-like state in a transition metal oxide LiV2O4 single crystal: indication of Kondo resonance in the photoemission spectrum

We have performed a vacuum ultraviolet laser excited photoemission spectroscopy on a d-electron heavy-fermion-like material LiV2O4 single crystal. We observed a sharp peak structure in the density of states at approximately 4 meV above the Fermi level (E(F)). The evolution of the peak height corresponds well with the crossover behavior to the heavy-fermion-like state as observed in the thermal and transport properties. The position, shape, and temperature (T) dependence of the peak structure is quite similar to the Kondo resonance observed in conventional f-electron heavy Fermion compounds.