F. Hulliger

Photoemission and inverse photoemission spectroscopy of NiO

Abstract Photoemission (UPS) and inverse photoemission (BIS) spectra of NiO grown as a thin film on metallic Ni are reported. The data are discussed with respect to the electronic structure of the occupied and empty states in NiO.

Low-temperature magnetic phase transitions of CeBi and CeSb

Specific heat, low- and high-field magnetic susceptibility, thermal expansion, and magnetostriction measurements have been made on single crystals of CeBi and CeSb in order to investigate the low-temperature magnetic phase transitions of these compounds. We have observed structural transitions at the respective Néel temperatures. The maximum tetragonal distortions below TN are of the order of 10−3 in both cases. Specific heat results confirm the unusually small overall splitting of the ground-state multiplet. Applications of external magnetic fields induce a variety of interesting effects and provide insight into the magnetic phase diagram of these substances. The results are discussed qualitatively.

Giant Kerr rotation and electronic structure of CeSbxTe1-x

Abstract Kerr rotation and ellipticity measurements in the 0.5–5 eV energy range and optical reflectivity data covering the photon energies 0.03–12 eV are presented for single crystals of CeSb, CeSb 0.75 Te 0.25 and CeTe. The (single) Kerr rotation of CeSb is found to exceed 14° which is by far the largest value ever observed. The energy of the 4f 1 → 5d transition of CeSb is determined to be ∼ 0.4 eV.

On the interpretation of valence band photoemission spectra of NiO

Abstract The valence band photoemission spectrum and the L 3 VV Auger spectrum of NiO are compared. The satellite found in the valence band of NiO and other Ni compounds is interpreted as an unscreened 3 d 7 final state, whereas the main d -emission is a 3 d 7 final state screened by a d electron in an exitonic state.

Surface binding energy shifts, mixed valence and localization of 4f electrons: Ce vs. Sm (invited)

Synchrotron radiation and x‐ray photoemission studies of ’’divalent’’ SmS, SmSe and ’’trivalent’’ SmSb as well as Sm metal strongly suggest the existence of a surface induced binding energy shift EsB (?0.5 eV to greater EB) of the 4f6 configuration in SmS and SmSe. The divalent surface component of Sm metal has been resolved spectroscopically and has EsB (4f6,6H) ∼0.8 eV relative to the Fermi energy EF. Resonance enhanced 4f emission has been used to determine EB for the 4f1 configuration in the metallic chalcogenides CeS, CeSe and CeTe as well as in the pnictides CeAs and CeN. A resonant two‐peak structure located at EF and at EB∼1 eV indicates a 4f surface binding energy shift of this magnitude in this fascinating ’’mixed valent’’ nitride. No shift could be resolved in the other Ce compounds having EB (4f1) between 1.8 and 2.6 eV. This is assigned to the more ’’band‐like’’, delocalized behaviour of 4f states in CeN. Constant‐final‐ and initial‐state spectra of CeN differ significantly from those of the ...

Superconductivity in rocksalt-type compounds

Abstract Rocksalt-type compounds with non-localized excess valence electrons appear to have a high likelihood of being superconducting above 0.3°K. Transition temperatures are reported for YS, YSe, YTe, LuS and LuSe.

Long range f.c.c. antiferromagnetic ordering of type III in YbAs

Abstract Neutron diffraction investigations performed at temperatures T ⩾ 7 mK on a single crystal of the rare-earth compound YbAs prove the existence of long-range f.c.c. antiferromagnetic ordering of type III, corresponding to k = [1, 0, ± 1 2 ] . The ordered magnetic saturation moments of magnitude μYb = 0.86(3) μB are oriented perpendicular to [0, 0, 1]. The phase transition at TN = 0.7 K is second-order, but the temperature dependence of the staggered magnetization exhibits a most unusual critical behaviour. A mean-field calculation indicates that the magnetic moments are stabilized by quadrupolar interactions.

Point contact spectroscopy of YbB12 and CeAl3

Abstract It will be shown that the first derivative of the current-voltage characteristic in point contact spectroscopy (PCS) is a function of the electronic density of states at the Fermi level Ef. PCS has been used to investigate an intermediate valent compound, YbB12, and a heavy Fermion system, CeAl3. It has been found that YbB12 has a hybridization gap and CeAl3 a density of states peak at Ef.

Antiferromagnetism in the ytterbium monopnictides YbX (X = N, P, As, Sb)

Neutron diffraction investigations prove the existence of long-range antiferromagnetic ordering of type III in stoichiometric YbN and YbAs and of type II in nonstoichiometric YbP. For stoichiometric YbSb no long-range antiferromagnetic ordering was found down to 7 mK. The crystal-field level scheme was established by neutron spectroscopy to be Γ6-Γ8-Γ7 for all compounds.

High-pressure behavior of CmBi and UBi

Abstract We report here high-pressure X-ray diffraction studies of the two actinide compounds, UBi and CmBi. These compounds existed initially in the NaCl-type (B1) crystal structure and each was studied at room temperature using a diamond anvil cell and energy dispersive X-ray diffraction analysis. The U and Cm monobismuthides were studied up to pressures of 42 and 48 GPa, respectively. All materials exhibited first-order crystallographic phase transitions from their NaCl-type (B1) to a CsCl-type (B2) structure, which were accompanied by volume collapses: UBi at 5 GPa (11% volume change); CmBi at 12 GPa (16% volume change). With curium monobismuthide a subsequent second-order transition from the CsCl-type structure to a tetragonal phase (indexed in space group P4/mmm) occured at 19 GPa. The bulk moduli and their pressure derivatives were derived for each material from the experimental pressure-volume relationships for the B1 phases. These values were: for UBi, 91 GPa and -5.4; for CmBi, 53 GPa and 8.1.