S. Gabáni

Magnetic and transport properties of TmB12, ErB12, HoB12 and DyB12

Abstract We present measurements of the magnetization and electrical resistivity of TmB 12 , ErB 12 and HoB 12 singlecrystalline samples as well as of a DyB 12 polycrystalline sample. Data were taken in the paramagnetic state as well as in the magnetically ordered regime. To our knowledge, this is the first systematic investigation of TmB 12 , ErB 12 , HoB 12 and DyB 12 on the magnetically ordered phase by measurements of magnetization and electrical resistivity. All samples investigated undergo antiferromagnetic ordering in the lower Kelvin temperature range. From the magnetization data, the Neel temperatures, the paramagnetic Curie temperatures, and the effective magnetic moments of the corresponding rare earth ions are determined. It is shown that the indirect exchange interaction of RKKY type is the dominating mechanism leading to the observed antiferromagnetic ordering. The measured temperature dependences of the electrical resistivity show a pronounced effect of superzone boundaries near Neel temperatures. The spin wave scattering of conduction electrons below T N is discussed, too.

Effects of disorder and isotopic substitution in the specific heat and Raman scattering in LuB12

Precision measurements of the specific heat and spectral intensity I(ω) of Raman scattering for LuNB12 single crystal samples with various boron isotopes (N = 10, 11, nat) have been performed at low and intermediate temperatures. A boson peak in the low-frequency part of the I(ω) spectrum has been observed for the first time for lutetium dodecaboride at liquid nitrogen temperatures. It has been shown that low-temperature anomalies in the specific heat, along with the features of Raman spectra, can be interpreted in terms of the transition to a cageglass state at T* = 50−70 K, which appears when Lu3+ ions are displaced from the centrosymmetric position in cavities of a rigid covalent boron sublattice towards the randomly located boron vacancies. The concentrations of various two-level systems that correspond to two types of vibrational clusters with correlation lengths of 12–15 and 18–22 Å, respectively, have been estimated. The vibrational density of states of LuB12 has been calculated from Raman spectra in the model of soft atomic potentials. An approach has been proposed to explain the dielectrization of the properties of the YbB12 compound at T < T*, as well as the features of the formation of magnetic structures in RB12 antiferromagnets (R = Tb, Dy, Ho, Er, Tm) and the suppression of superconductivity in LuB12.

Antiferromagnetic instability and the metal-insulator transition in Tm1 − xYbxB12 rare earth dodecaborides

The magnetic and transport characteristics of substitutional solid solutions of the Tm1−xYbxB12 rare earth dodecaborides have been investigated. The measurements performed in the wide temperature range 1.8−300 K on the high-quality single-crystalline samples make it possible to conclude that as x increases, antiferromagnetic instability develops with the quantum critical point (TN = 0) near x = 0.3 and relevant dielectrization of the electron structure in the range 0 ≤ x ≤ 0.8 takes place. With the results of the thermoelectric measurements in Tm1−xYbxB12, the activation energy values and their dependence on x have been determined.

Samarium hexaboride is a trivial surface conductor

SmB6 is predicted to be the first member of the intersection of topological insulators and Kondo insulators, strongly correlated materials in which the Fermi level lies in the gap of a many-body resonance that forms by hybridization between localized and itinerant states. While robust, surface-only conductivity at low temperature and the observation of surface states at the expected high symmetry points appear to confirm this prediction, we find both surface states at the (100) surface to be topologically trivial. We find the

Pressure-Induced Localization of 4f Electrons in the Intermediate Valence Compound SmB6

{\bar{\varGamma }}

Specific heat of CexLa1 − xB6 in the low cerium concentration limit (x ≤ 0.03)

Γ̄ state to appear Rashba split and explain the prominent

Specific features of the formation of the ground state in PrB6

\bar X