Jerzy Goraus

The magnetic and transport properties of Fe2VGa doped with metal M (M = Rh and Ti) have been obtained from the analysis of ac magnetic susceptibility chiac, magnetization M vs magnetic field, specific heat C, and electrical resistivity rho. The results provide evidence for the formation of a spin-glass state at Tf˜6 K, resulting from an atomic disorder. Short-range magnetic correlations manifested at T>Tf as anomalies of the low magnetic field ac magnetic susceptibility and specific-heat data are believed to be related to a Griffiths-like phase in Fe2V1-xMxGa at x<xc˜0.15.

The effect of La doping of CeRhSb has been studied with the help of electrical resistivity, magnetic susceptibility, and specific-heat measurements for the system of Ce1-xLaxRhSb with x<0.2 . Particular emphasis is put on the extreme low-doping regime, x˜0.02 . Namely, we show that the resistivity increase induced by appearance of the Kondo gap for x=0 is transformed into that caused by itinerant f holes and appears already for x=0.02 . The studies indicate also that a spin-glasslike behavior, intermixed with a ferromagnetic component in these materials, is induced by statistical distribution of La ions. Our study also shows that the Kondo gap in CeRhSb is very sensitive to the magnitude of hybridization V between the 4f -electron and the conduction-electron states. The results for the system Ce1-xLaxRhSb are interpreted in terms of (narrow) Kondo-hole band, located near at the Fermi level, that gives rise to an abrupt transition from the Kondo-insulator regime to a metallic state via an intermediate step (at very low doping) involving formation of the ferromagnetic clusters containing a Kondo hole (i.e., magnetic polarons). Finally, a comparison between Ce1-xLaxRhSb with Ce1-xLaxNiSn systems is carried out to contrast the concept of the polarons in Ce1-xLaxRhSb with their absence in the latter system due to the dominant antiferromagnetic interaction among the 4f1 spins.

CeNiSn is known as a semimetallic system with a small pseudogap at the Fermi energy. We investigate the effect of Rh doping on the Kondo insulator CeNiSn by means of measurements of ac magnetic susceptibility and specific heat. We show that the formation of the Kondo insulator narrow gap in CeNi1 - xRhxSn is associated with disorder-induced f-electron localization. For doped CeNiSn with x <= 0.06, the electrical resistivity data follow an activation and variable range hopping behaviour at low T, consistent with weak disorder and localization, while C/T is large, which is not a common feature of Kondo insulators. For x > 0.06, the system is metallic and exhibits non-Fermi liquid behaviour with magnetic susceptibility χ ~ T - n with n ~ 0.4 and electrical resistivity ρ ~ T.

ABSTRACT Ferromagnetic compound CeAgGa crystallizes in CeCu2Imma structure with Ag and Ga atoms distributed randomly at 8h position. We report X-ray photoemission (XPS) valence-band spectra for CeAgGa and compare the results with those obtained from the full potential linear augmented plane-wave (FP-LAPW) method. In order to study the influence of the atomic disorder at 8h sites on the calculated density of states (DOS) we analysed different geometries of the unit cell, possible for CeAgGa. We found that neither disorder nor Ce 4f electron correlations, when they are also taken into account, do give satisfactory agreement between the calculated DOSs and the XPS spectra. We show, however, that inclusion of a Coulomb repulsion U on the Ag 4d states yields a good result. We also report that disorder in Ag/Ga layers leads to the localization of the Ag 4d states. Magnetic moments on Ce atoms from our calculations are in good agreement with those obtained experimentally and the ferromagnetic ground state is energetically preferred. The valence of Ce ions close to 3+ has also been confirmed by the Ce 3d XPS spectra.

ABSTRACT We present temperature dependant studies of Cr K, Ni K and Se K absorption edges of ZnCr1.8Ni0.2Se4 and NiCr2Se4. The EXAFS and XANES analysis is consistent with nickel located on the octahedral site. The experiment is compared with the results of the FPLO-CPA numerical calculations and the angular momentum projected densities of states. The calculations reveal that both nickel (0.5μB) and selenium (0.1μB) possess magnetic moment and are polarised opposite to chromium (3.1μB). Calculation results imply contribution from Se 4p electrons to the magnetism and Cr/Ni 4s to charge balance of the system.

The effect of La doping of CeRhSb has been studied with the help of electrical resistivity, magnetic susceptibility, and specific-heat measurements for the system of Ce1-xLaxRhSb with x&amp;amp;amp;amp;amp;amp;lt;0.2 . Particular emphasis is put on the extreme low-doping regime, x˜0.02 . Namely, we show that the resistivity increase induced by appearance of the Kondo gap for x=0 is transformed into that

The magnetic and transport properties of Fe2VGa doped with metal M (M = Rh and Ti) have been obtained from the analysis of ac magnetic susceptibility chiac, magnetization M vs magnetic field, specific heat C, and electrical resistivity rho. The results provide evidence for the formation of a spin-glass state at Tf˜6 K, resulting from an atomic disorder. Short-range magnetic

ABSTRACT Ce5Rh4Sn10 is known as a heavy-fermion antiferromagnet with magnetic-ordering temperature T N2 = 4.3 K. We report a new antiferromagnetic phase transition at T N1 = 1.4 K. In the series of Ce1−x La x Rh4Sn10 compounds both magnetic phase transitions at T N1 and T N2 shift towards lower temperatures. For Ce3La2Rh4Sn10 and Ce3.5La1.5Rh4Sn10 we found only one transition. In the temperature region T N1&amp;lt;T&amp;lt;T N2, the magnetization M measured as a function of magnetic field H exhibits a large jump at very low fields of 0.03 T with a very small hysteresis loop. This abnormal behavior could be due to spin-flip transitions. Thermodynamical properties of the series of Ce1−x La x Rh4Sn10 compounds are discussed in terms of the antiferromagnetic Kondo lattice.

The aim of this work is to investigate electronic structure, magnetic properties and electrical resistivity of Fe(2)V(1-x)Ti(x)Al Heusler alloys. Numerical calculations give a pseudogap at the Fermi level for the majority-spin band of Fe(2)TiAl and a magnetic moment larger than 0.9 μ(B), whereas the ground state of Fe(2)VAl is calculated as a nonmagnetic semimetal with a very low total density of states at the Fermi level. In our calculations the remaining alloys of the Fe(2)V(1-x)Ti(x)Al series are nonmagnetic for x&amp;lt;0.1 and weakly magnetic for 0.1&amp;lt;x≤1. The magnetic moment μ of the series of Fe(2)V(1-x)Ti(x)Al compounds scales with the number of valence electrons and fits well to the Slater-Pauling curve. We also present a study of the electronic transport properties and magnetic susceptibility. The resistivities ρ(T) of Fe(2)VAl and Fe(2)V(0.9)Ti(0.1)Al are large and exhibit a negative temperature coefficient dρ/dT of the resistivity between 2 and 300 K. Below 20 K, ρ(T) also shows an activated character. The magnetic susceptibility of Fe(2)VAl and Fe(2)V(0.9)Ti(0.1)Al shows a maximum at ∼2 K which could reflect either the disorder effect or the hybridization gap, characteristic of Kondo insulators.

We present investigations of the magnetic and electric transport properties, specific heat, and electronic structure of the intermetallic and strongly correlated system of CeRhSn(1-x)In(x) compounds. The main goal of this paper is to determine the hybridization energy between the f electron and conduction electron states, V(cf), and its influence on the ground state properties of the system. The complementary experimental data are discussed on the basis of the Anderson model for a periodic Kondo lattice. CeRhSn is known as a non-Fermi liquid, while CeRhIn is a valence fluctuating system. We discuss the ground state properties of CeRhSn(1-x)In(x) and compare the results with those obtained for the doped Ce-based Kondo insulators.

CeNiSn is known as a semimetallic system with a small pseudogap at the Fermi energy. We investigate the effect of Rh doping on the Kondo insulator CeNiSn by means of measurements of ac magnetic susceptibility and specific heat. We show that the formation of the Kondo insulator narrow gap in CeNi(1 - x)Rh(x)Sn is associated with disorder-induced f-electron localization. For doped CeNiSn with x ≤ 0.06, the electrical resistivity data follow an activation and variable range hopping behaviour at low T, consistent with weak disorder and localization, while C/T is large, which is not a common feature of Kondo insulators. For x &amp;gt; 0.06, the system is metallic and exhibits non-Fermi liquid behaviour with magnetic susceptibility χ ∼ T( - n) with n ∼ 0.4 and electrical resistivity ρ ∼ T.

In this paper we present experimental results obtained for CePdBi by means of specific heat, electrical resistivity, magnetization and x-ray photoemission spectroscopy (XPS) measurements as well as fully relativistic band structure calculations. CePdBi crystallizes in MgAgAs structure and exhibits a transition to a magnetically ordered state at TM ~/= 2 K, and a subsequent transition to a superconducting state at TC ~/= 1.3 K. The superconducting phase has a significant critical field of about 1.4 T. The x-ray diffraction, resistivity and magnetic susceptibility data show that CePdBi exhibits significant atomic disorder, which is a typical feature of Heusler alloys. It seems that the superconducting transition is caused by part of the disordered phase, which from the Meissner shielding can be estimated to constitute ~8% of the sample volume. Due to atomic disorder, CePdBi exhibits metamagnetic behavior below TM and spin-glass-like features just above TM. Band structure calculations confirm the magnetic ground state of the CePdBi system and the possibility of formation of a narrow pseudogap near the Fermi level, which can also be seen in resistivity data. The spin-orbit interaction strongly influences the band structure and the shape of the semiconducting gap.