Anomalous charge transport in dodecaborides RB12 (R- Ho, Er, Tm, Lu) (original) (raw)
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Anomalous charge transport in RB12 (R = Ho, Er, Tm, Lu)
physica status solidi (b), 2006
High precision measurements of Hall R H (T) and Seebeck S(T) coefficients have been carried out for the first time on single crystals of rare earth dodecaborides RВ 12 (R -Ho, Er, Tm, Lu) at temperatures 1.8 -300K. Low temperature anomalies associated with antiferromagnetic phase transitions in HoВ 12 , ErВ 12 and TmВ 12 compounds have been detected on the temperature dependencies of R H (T) and S(T). The estimated values of charge carriers' mobility allowed us to conclude about the appreciable influence of spin fluctuations on the charge transport in these compounds with B 12 atomic clusters.
Features of the local structure of rare-earth dodecaborides RB12 (R = Ho, Er, Tm, Yb, Lu)
JETP Letters, 2013
Rare earth dodecaborides RB 12 crystallize in a NaCl type lattice, where rare earth ions R 3+ occupy Na positions and cuboctahedra B 12 are located at Cl positions ( ) . As a result, the rare earth ion in the first coordination shell is surrounded by 24 boron atoms forming a truncated octahedron. The radius of this octahedron (~2.78 Å) is much larger than the sum of the covalent radius of boron (0.88 Å) [1] and the radius of R 3+ ions (Շ1.0 Å) . The strong covalent bonds of boron atoms are responsible for a high rigid ity of the boron sublattice and the structure as a whole, as well as high chemical stability, high microhardness, high melting temperature, and higher electrical and thermal conductivities as compared to the respective rare earth metals . Difference in the filling of the 4f level provides a wide variety of electronic and magnetic properties of dodecaborides, whereas the weakness of the bonds of rare earth ions between each other and with the boron sublattice is responsible for their strong dependence on the temperature and mag netic field. In particular, HoB 12 , ErB 12 , and TmB 12 compounds are antiferromagnets with the Néel tem peratures Θ N = 7.38, 6.65, and 3.28 K, respectively [1]; YbB 12 is considered as a Kondo insulator with the Kondo temperature T K ~ 70 K [6]; and LuB 12 is a superconductor with the critical temperature T c = 0.44 K . Strong electron correlations depending on the features of the local environment of rare earth ions additionally affect the properties of rare earth dode caborides.
Transport Properties of Rare Earth Dodecaborides at Low Temperatures 1
2006
We present results of electrical resistivity measurements on HoB12, ErB12 and TmB12 single crystalline samples in the temperature range of 1.6-30 K and in magnetic field up to 6 T. From the received data, B vs. T phase diagrams of all samples were created. Spin wave scattering of conduction electrons in the antiferromagnetic phase and the scattering of electrons in the paramagnetic phase are analysed and discussed.
Hall effect and magnetic ordering in RB12
Low Temperature Physics, 2009
The concentration of carriers in LuB 12 is evaluated theoretically by applying ab initio FP-LMTO calculations. Theoretical results are found to be in agreement with high precision measurements of the Hall R H (T) coefficient which were carried out on single crystals of the rare earth dodecaborides RB 12 (R = Ho, Er, Tm, Lu) at temperatures 1.8-300 K. A nature of the antiferromagnetic ordering in RB 12 is investigated within the RKKY-like model, which was supplemented by comprehensive electronic structure calculations for paramagnetic, ferromagnetic and antiferromagnetic phases.
Phonon Drag and Magnetic Anomalies of Thermopower in RB12 R Ho, Er, Tm, Lu
Acta Physica Polonica Series a
High precision measurements of the Seebeck coefficient S(T) were carried out on the single crystals of RB 12 (R = Ho, Er, Tm, Lu) at temperatures 2-300 K. It was shown that the effects of phonon drag result from vibrations of rare earth ions (ωE ≈ 10-33 meV) in the rigid framework structure of the B 12 clusters and determine the main contribution to thermopower at intermediate temperatures (30-300 K). The correlated behavior of transport parameters favors the appreciable enhancement of spin fluctuations in the sequence of magnetic compounds (HoB12-TmB12) when approaching to the valence instability state in YbB 12. The giant increase in S(T) detected in the vicinity of the Néel temperature TN for HoB12, ErB12, and TmB12 seems to result from the density of states renormalization caused by antiferromagnetic ordering.
Magnetic Properties of Some Rare Earth Dodecaborides
We present results of magnetic measurements performed on TmB12, ErB12, H o B 12 single-crystalline samples and on a DyB12 poly-crystalline sample in 9.5 mT magnetic field and at temperatures between 1.6 K and 300 K. From the observed dependences, which refer to antiferromagnetic ordering in all samples, their N eel temperatures, paramagnetic Curie temperatures, and the effective magnetic moments of the corresponding rare earth ions were determined. The obtained results are compared with values received by other measurements.
arXiv: Strongly Correlated Electrons, 2018
Structure differences of isotopically different dodecaborides LuNB12 (N = 10, 11, natural) and their impact on thermal and charge transport characteristics of the crystals have been first discovered. Atomic displacement parameters (ADPs) of Lu and B atoms are described in terms of the Einstein and Debye models, respectively. Characteristic Einstein and Debye temperatures are calculated directly from the x-ray data and corresponding ADPs are separated into temperature dependent and temperature independent components. The first component is a measure of thermal atomic vibrations whereas the second one is a sum of zero vibrations and static shifts of some atoms from their crystallographic positions. Such a local disordering is more expressed in LunatB12 with 10B : 11B = 1 : 4 judging both from the large static ADP components and the Schottky anomalies in the heat capacity. Crystal structures are refined in Fm3-m group but certain distortions of the ideal cubic unit-cell values are obse...
Magnetic structure and bonding of rare-earth diboride compounds RB2: First-principles calculations
physica status solidi (b), 2012
The electronic structure and magnetic behavior of hexagonal rare-earth diboride RB 2 are studied using ab initio densityfunctional theory in the DFT þ U approach. The effect of the spin-orbit coupling is also investigated and it is found to be a necessary requirement for the accurate description of the magnetic moment. In this paper, we study the magnetic phase stability of RB 2 compounds; the band structure and the density of state (DOS) results prove that the coulomb potential and the spin-orbit interaction are keys factors to understand the magnetic properties of these series of materials. In addition, we also explain the behavior of a chemical bond of RB 2 compounds through the analysis of the DOS and of the charge density.
Magnetism of rare earth tetraborides
Journal of Physics: Conference Series, 2010
The rare earth tetraborides REB4 with RE = Ho, Er, Tm, crystallize in a tetragonal lattice where the positions of the RE ions can be mapped to a Shastry Sutherland lattice. We have investigated the magnetic properties by means of magnetisation and specific heat experiments in a magnetic field. All compounds are anisotropic, with RE= Er, Tm they are strong Ising magnets, for RE = Ho we find xy anisotropy. In magnetic field we find complex behaviour with a number of different phases as a function of applied field, field direction and temperature. Remarkable is the observation of fractional magnetisation plateaux for magnetic field || (001) in HoB4 and TmB4.