I. P. Sadikov

Magnetic excitation spectrum of mixed-valence SmB6 studied by neutron scattering on a single crystal

The paramagnetic response of mixed-valence samarium hexaboride has been studied by inelastic neutron scattering using a low-absorption double-isotope single crystal of 154Sm11 B6. Measurements were performed for energy transfers 0<or=h(cross) omega <or=50 meV at temperatures ranging from 2 to 100 K. Two main contributions were observed in the spectra: a broad intermultiplet transition of single-ion type at h(cross) omega approximately=36 meV, and a narrow low-energy excitation centred at h(cross) omega approximately=14 meV, which is strongly anisotropic and temperature dependent and exhibits a weak but visible dispersion. The latter excitation appears to be an inherent feature of the mixed-valence state due to f-electron hybridization effects, which denotes the formation of a local bound state around the Sm sites.

Lattice Dynamics of Intermediate Valence Semiconductor SmB6.

All acoustic and the lowest optic branches in three main symmetry directions have been determined by inelastic neutron scattering at room temperature using a double isotope monocrystal 154Sm11B6. In comparison with the integer valence system LaB6 the phonons are softer, and the LA branches exhibit remarkable anomalies. These features are interpreted on the basis of a specific coupling of the lattice vibrations with the dipole (f-d) and monopole (f-f) excitations of the Sm shells, the latter being characteristic for the mixed valence semiconductor. A weak broad signal has been observed in the energy gap between acoustic and optic modes, which can be ascribed to an additional mode appearing due to the nonadiabatic interaction of phonons with valence fluctuations.

Neutron Scattering Study of the Intermediate-Valent Ground State in SmB6

Inelastic-neutron-scattering spectra were measured on the polycrystalline double isotopic sample 154Sm 11B6 in a wide range of the energy transfer. The intermultiplet transitions corresponding to f6 and f5 configurations of the intermediate-valent state of the Sm ion, as well as a low-energy excitation with unusual momentum transfer and temperature dependences have been observed in the magnetic part of the scattering function.

Magnetic excitations in SmB6 single crystals

Abstract Two, essentially dispersionless, magnetic excitations, at energies ℏ ω 1 ≃ 36 and ℏ ω 2 ≃ 14 meV, have been investig ated by inelastic neutron scattering measurements on a single crystal of mixed-valent 154 Sm 11 B 6 . The latter one decreases markedly upon heating, or with increasing | Q | . It is ascribed to the spin-flip of 5d electrons which form a bound state with the 4f electrons of a given site by tunnelling over the octahedron defined by its six nearest Sm neighbours.

Low-temperature effects in magnetic spectral response of CeAl3-based systems

Magnetic excitation spectra of Ce ions in CeAl3 and in the substituted systems Ce0.9Y0.1Al3 and Ce0.9Gd0.1Al3 were studied by inelastic neutron scattering in the temperature range 0.03 K < T < 100 K. Below ≈ 60 K peak positions are strongly temperature dependent. The effect is enhanced due to chemical pressure and looks like a pure single ion feature given by the interaction of the Ce ion with the conduction electrons. Additional investigations of the spectra of the paramagnetic impurity ion Pr3+ in CeAl3 and in the reference system LaAl3 showed an anomalous attenuation of the relaxation broadening for the CEF excitations in the CeAl3 matrix. All observed features are interpreted as a consequence of the Kondo ground state formation, strongly influenced by the interaction between the crystalline electric field and the local moment of the Ce Kondo ion.

Temperature effects in phonon dispersion of SmB6 intermediate valence semiconductor

Abstract Temperature dependence of previously discovered anomalies in SmB 6 acoustic and low-lying phonon branches was investigated on three-axis and time-of-flight spectrometers. The largest changes in phonon frequencies with respect to the room temperature data were found for longitudinal branches while all transverse phonons hardened slightly. The unusual nature of the previously observed dispersionless mode in the energy gap between acoustic and optic phonons was confirmed. Some new peculiarities of the SmB 6 excitation spectra were obtained at low temperature.

Neutron spectroscopy of Pr3+ impurity in the intermediate-valence compound CeNi5

Abstract The experimental study of the effect of cerium ions in the intermediate-valence (IV) state on the crystal electric field (CEF) measured on the paramagnetic ion of praseodymium being a part of the compound (Pr)CeNi5 as a substitution impurity, was performed. The experiments were carried out with the aid of neutron inelastic scattering within the range of sample temperatures of 4.3–50 K. The strong change of the CEF potential in the IV system was found relative to the structural analog without IV-ions. The additional contribution to the CEF seems to be associated with the change in the compound electron subsystem due to IV-ions f-electrons delocalization. It was determined that in forming an additional contribution to the CEF, a significant part was played by correlation effects between IV-ions.

Soft Mode and Magnetic Phase Transition in PrNi

The spectrum of magnetic excitations in a single crystal of intermetallic compound PrNi was studied by inelastic neutron scattering. Experiment showed the substantial softening of some collective magnetic excitation modes near the ferromagnetic ordering temperature Tc≈20 K. The result is analyzed within the framework of a model that describes the magnetic phase transition in systems with induced magnetic moment.

Imperfection of the Sm sublattice and valence instability in compounds based on SmB6

The magnetic susceptibility, electrical resistance, specific heat, and thermal expansion coefficient of SmB6, Sm0.8B6, and Sm1–xLaxB6 (x=0.1 and 0.2) are measured in the temperature range T=4–300 K. The dispersion curves of the acoustic phonon branches in lanthanum-doped samples are studied. A combined analysis of the results confirms the existence of an activation gap in the electron density of states in both nonstoichiometric and lanthanum-doped compounds. The anomalies in the electronic component of the thermal expansion coefficient are associated to a considerable degree with the temperature variation of the valence and, like the magnetic susceptibility, reflect features of the f-electron excitation spectrum. It is found that lanthanum doping does not lead to significant changes in the anomalies in the phonon spectrum of SmB6. It is established that the homogeneous intermediate-valent state of the samarium ion is fairly stable and is maintained when the perfection of the Sm sublattice is violated.

Local singlet bound state and magnetic excitations in mixed-valence SmB6

Abstract The recent observation of an unconventional magnetic excitation at h z.shtsls; ω = 13–14 meV in SmB 6 may be one of the key results for understanding the nature of the mixed-valence state in this system. A detailed neutron scattering study of this feature has been carried out as a function of momentum transfer and temperature, and the results obtained support a picture in which the electron released from the 4f shell forms a local bound state on an extended orbital around the original site.