Accurate low temperature charge transport measurements in combination with high-precision x-ray diffraction experiments have allowed detection of the symmetry lowering in the single domain ...Tm0.19Yb0.81B12 crystals that belong to the family of dodecaborides with metal-insulator transition. Based on the fine structure analysis we discover the formation of dynamic charge stripes within the semiconducting matrix of Tm0.19Yb0.81B12. The charge dynamics in these conducting nano-size channels is characterized by broad-band optical spectroscopy that allowed estimating the frequency (~2.4 × 1011 Hz) of quantum motion of the charge carriers. It is suggested that cooperative Jahn-Teller effect in the boron sublattice is a cause of the large-amplitude rattling modes of the Tm and Yb ions responsible for the 'modulation' of the conduction band along one of the directions through the variation of 5d-2p hybridization of electron states.
A detailed study of charge transport in the paramagnetic phase of the cage-cluster dodecaboride Ho0.8Lu0.2B12 with an instability both of the fcc lattice (cooperative Jahn–Teller effect) and the ...electronic structure (dynamic charge stripes) was carried out at temperatures 1.9–300 K in magnetic fields up to 80 kOe. Four mono-domain single crystals of Ho0.8Lu0.2B12 samples with different crystal axis orientation were investigated in order to establish the singularities of Hall effect, which develop due to (i) the electronic phase separation (stripes) and (ii) formation of the disordered cage-glass state below T*~60 K. It was demonstrated that a considerable intrinsic anisotropic positive component ρanxy appears at low temperatures in addition to the ordinary negative Hall resistivity contribution in magnetic fields above 40 kOe applied along the 001 and 110 axes. A relation between anomalous components of the resistivity tensor ρanxy~ρanxx1.7 was found for H||001 below T*~60 K, and a power law ρanxy~ρanxx0.83 for the orientation H||110 at temperatures T < TS~15 K. It is argued that below characteristic temperature TS~15 K the anomalous odd ρanxy(T) and even ρanxx(T) parts of the resistivity tensor may be interpreted in terms of formation of long chains in the filamentary structure of fluctuating charges (stripes). We assume that these ρanxy(H||001) and ρanxy(H||110) components represent the intrinsic (Berry phase contribution) and extrinsic (skew scattering) mechanism, respectively. Apart from them, an additional ferromagnetic contribution to both isotropic and anisotropic components in the Hall signal was registered and attributed to the effect of magnetic polarization of 5d states (ferromagnetic nano-domains) in the conduction band of Ho0.8Lu0.2B12.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Abstract
Randomness and frustration are believed to be two crucial criteria for the formation of spin glass state. However, the spin freezing occurs in some well-ordered crystals below the related ...temperature
T
f
due to the instability of each spin state, which induces the variation of either magnetic moment value or exchange energy. Here we explore the new mechanism of the in-site originated disorder in antiferromagnets Gd
0.73
La
0.27
B
6
and GdB
6
, which is caused by the random mutual shifts of Gd
3+
spins from the centrally symmetrical positions in the regular cubic lattice. The universal scaling of ESR linewidth temperature dependencies to the power law
ΔH
(
T
) ~ ((
T
−
T
D
)
/T
D
)
α
with
α
= − 1.1 ± 0.05 in the paramagnetic phase of both compounds demonstrates the identity of the origin of magnetic randomness. In Gd
0.73
La
0.27
B
6
the resulting random spin configurations freeze at
T
f
≈ 10.5 K where the maximum of magnetization is observed. Below
T
f
the splitting of ZFC and FC magnetization curves takes place as well as the magnetic state depends on the antecedent sample history. In the case of GdB
6
the coherent displacement of Gd ions compete with these random shifts forming an antiferromagnetic (AFM) phase at
T
N
= 15.5 K, which prevails over the spin freezing at
T
f
≈ 13 K, expected from the ESR data. The observation of the hysteresis of the ESR spectrum in the AFM phase suggests that its properties may be determined by the competition of two types of AFM orders, which results in formation of stable magnetic domains with nonequivalent positions of AFM Gd pairs at
T
< 10 K.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
•Adjacent double-ZGV dispersion curves.•Narrow-band ZGV multiplication.•Multi-peak frequency response.•Modal excitability in multi-ZGV bands.•ZGV manifestation or non-manifestation under different ...loads.
To date, the phenomenon of zero group velocity (ZGV) Lamb wave in a stress-free elastic plate has been well studied and used in non-destructive material characterization, electroacoustic devices and some other applications. This phenomenon is associated with the backward mode appearing in the range limited by the ZGV and cutoff frequencies. The modal frequency response of the structure, primarily the spectrum of the corresponding guided wave (GW) excited in the plate by a force source, is featured by a sharp peak at the ZGV frequency, allowing its experimental detection. Other peaks appearing at the cutoff frequencies indicate thickness resonances. In a layered half-space of infinite thickness, the backward-mode bend of the dispersion curve turns into a double bend that gives rise to three GWs associated with the same branch (one backward and two forward modes). Moreover, several adjacent branches with double bends, and, thus, several peaks, can appear in a narrow range as the number of layers increases, indicating multiple ZGV resonances. Such dispersion curves with double ZGV points were also found in waveguides of finite thickness with anisotropic or contrast material properties; however, their resonance manifestation is poorly studied. In this article, we consider and discuss several kinds of multi-peak ZGV responses using examples of layered samples of various materials. Along with the expected increase in the number of peaks in multilayer structures with contrast layers, it was noted that some ZGV points may or may not appear in peaks, depending on the type of load.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Seebeck effect in the crystalline samples of EuxYb1-xB6(x= 0, 0.082, 0.127, 0.9, 1) was investigated at temperatures 2-300 K. For all the compounds thermopower is shown to be well described by the ...sum of diffusion (Sd=AT) and phonon drag components. The latter contribution is induced by quasilocal (Einstein) modes of ytterbium and europium ions with characteristic temperatures ΘE(YbB6) ≈ 91 K and ΘE(EuB6) ≈ 122 K. The estimation of effective massm*of the charge carriers proves that increasing of Eu content induces crossover from 'heavy' holes withmh*(x⩽ 0.127) ≈ 0.3-0.36m0to 'light' electrons withme*(x⩾ 0.9) ≈ 0.12-0.13m0(m0-free electron mass). For the Eu-rich compounds we propose the existence of additional point on the phase diagram, which corresponds to short-range magnetic order with enhanced spin fluctuations preceding the stabilization of magnetic polarons.
Abstract
Introducing of topological insulator concept for fluctuating valence compound – samarium hexaboride – has recently initiated a new round of studies aimed to clarify the nature of the ground ...state in this extraordinary system with strong electron correlations. Here we discuss the data of magnetic resonance in the pristine single crystals of SmB
6
measured in 60 GHz cavity experiments at temperatures 1.8–300 K. The microwave study as well as the DC resistivity and Hall effect measurements performed for the different states of SmB
6
110 surface prove definitely the existence of the layer with metallic conductivity increasing under lowering temperature below 5 K. Four lines with the g-factors g ≈ 2 are found to contribute to the ESR-like absorption spectrum that may be attributed to intrinsic paramagnetic centers on the sample’s surface, which are robust with respect to the surface treatment. The temperature dependence of integrated intensity
I
(
T
) for main paramagnetic signal is found to demonstrate anomalous critical behavior
I
(
T
) ~ (
T
*
−
T
)
ν
with characteristic temperature
T
*
= 5.34 ± 0.05 K and exponent ν = 0.38 ± 0.03 indicating possible magnetic transition at the SmB
6
110 surface. Additional resonant magnetoabsorption line, which may be associated with either donor-like defects or cyclotron resonance mode corresponding to the mass
m
c
~ 1.2
m
0
, is reported.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
The transverse magnetoresistance of Ho
0.8
Lu
0.2
B
12
dodecaboride with a cage glass structure is studied at low (2–10 K) temperatures. It is demonstrated that the isotropic negative ...magnetoresistance in this antiferromagnet is dominant within the broad temperature range near
T
N
≈ K. This contribution to the total magnetoresistance is due to the scattering of charge carriers by nanoclusters formed by Но
3+
ions, and it can be scaled in the ρ =
f
(μ
2
eff
H
2
/
T
2
) representation. It is found that the magnetoresistance anisotropy above (about 15% at 80 kOe) is due to the positive contribution, which achieves maximum values at the magnetic field direction close to
H
║ 001. The anisotropy of the charge carrier scattering is interpreted in terms of the cooperative dynamic Jahn−Teller effect at В12 clusters.
Full text
Available for:
DOBA, EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, IZUM, KILJ, KISLJ, MFDPS, NLZOH, NUK, OBVAL, OILJ, PILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, SIK, UILJ, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
Spatial anisotropy generated spontaneously in the translationally invariant metallic phase, i.e. electron nematic effect, addresses a great challenge for both experimentalists and theoreticians. An ...interesting option for the realization of the electron nematic phase is provided by the system with orbital ordering, as long as both orbitally ordered states and electron nematic phases possess broken spatial symmetry. Here we report the detailed study of the angular dependences of the magnetoresistance in the orbitally ordered antiferroquadrupole (AFQ) phase of CeB
6
. Our data allowed revealing the electron nematic effect, which develops when magnetic field exceeds a critical value of 0.3–0.5T. As a result, new transition inside the AFQ phase corresponding to the change of the symmetry of magnetic scattering on spin fluctuations in CeB
6
is discovered.
Full text
Available for:
IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Display omitted
•Breakup conditions and characteristics were established for droplets of waste-derived fuels, when ignited.•Droplets breakup enhances burning out of fuel components (fine coal and ...oil).•Both ignition delay time and combustion duration do not exceed 5 s.•A large group of properties was analyzed for separate fuel components.•Hypothesis was formulated about the influence of fuel composition on droplets breakup.
This research is focused on the ignition and combustion mechanisms and characteristics of single droplets of seven different composite liquid fuels, based on wet coal processing waste (fine coal + 50 wt% of water) with 40 wt% of vegetable oils (castor, rapeseed) and used petroleum-based oils (lubricants – motor, compressor, and turbine oils; working fluid – hydraulic oil; insulating fluid – transformer oil). The combustion of waste-derived fuel suspensions is initiated by introducing single droplets into heated motionless air with a temperature of 700–1,000 °C. Threshold conditions (component composition, concentration of combustible liquid, and temperature) were detected, for which micro-explosions during the induction period resulted in the full breakup of droplets, combustion of products (vapors and fine particles) and their subsequent rapid burnout. A high-speed video recording system is used to establish consistent patterns of physical and chemical processes, as well as ignition and combustion characteristics (ignition delay times, burnout time, velocity of breakup products, and size of their burnout area) for a group of fuels under the conditions of droplet breakup. A hypothesis about how the composition of the component affects the breakup of droplets during ignition was formulated based on the results of analyzing the properties (initial boiling point and evaporation rates of oils, their surface tension and surface free energy, as well as wettability of dry coal processing waste) of separate fuel components.
Full text
Available for:
GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
PDF
