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.
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.
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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.
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Heavy-fermion metals exhibit a plethora of low-temperature ordering phenomena . Among these are the so-called hidden-order phases that, in contrast to conventional magnetic order, are invisible to ...standard neutron diffraction experiments. One of the structurally most simple hidden-order compounds, CeB6, has been intensively studied for an elusive phase that was attributed to the antiferroquadrupolar ordering of cerium-4f moments . As the ground state of CeB6 is characterized by a more conventional antiferromagnetic (AFM) order , the low-temperature physics of this system has generally been assumed to be governed solely by AFM interactions between the dipolar and multipolar Ce moments . Here we overturn this established picture by observing an intense ferromagnetic (FM) low-energy collective mode that dominates the magnetic excitation spectrum of CeB6. Inelastic neutron-scattering data reveal that the intensity of this FM excitation significantly exceeds that of conventional spin-wave magnons emanating from the AFM wavevectors, thus placing CeB6 much closer to a FM instability than previously anticipated. This propensity for ferromagnetism may account for much of the unexplained behaviour of CeB6, and should lead to a re-examination of existing theories that have so far largely neglected the role of FM interactions.
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IJS, IZUM, KILJ, KISLJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Antiferromagnetic resonance in GdB6 exhibits a series of anomalous features such as jump of the resonance position at TN = 15.5 K and resonance evolution to four line structure with further ...temperature decrease. Here we report the study of temperature behaviour of antiferromagnetic resonance modes v(H0) in AFM phase. We analyzed v(H0) dependencies at several temperatures T < TN within the model of an antiferromagnet with easy anisotropy axis. In the result we have demonstrated that AFMR behaviour is determined by two following factors: (i) abrupt change of the gyromagnetic ratio γ at TN, which remains constant (corresponding to g-factor g = 1.27) in AFM phase and (ii) jump of zero field frequency v0 (from v0 ≈ 0 to v0 ≈ 20 GHz at TN with its further growth to v0 ≈ 35 GHz at T = 1.9 K.
Studies of dodecaboride LuB
12
in the temperature range of 10–300 K show that the
175
Lu spectrum is broadened due to the scatter of quadrupole frequency shifts caused by the defects in the Lu ...sublattice. To explain the discovered hysteresis in the temperature dependence of the
175
Lu linewidth, a scenario of “crystallization of structural defects” is proposed, in which the defects of the Lu sublattice, disordered at room temperature, are transformed into a more symmetrical and stable configuration with decreasing temperature, apparently due to static distortions of the boron frame caused by the cooperative Jahn–Teller effect.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
For the first time, an electronic phase transition at
T
c
≈ 340 K in a classical strongly correlated electron system CeB
6
is discovered and studied in detail. It is shown that the observed anomalies ...in the resistivity, thermal conductivity, specific heat, magnetization, and lattice parameters apparently correspond to the formation of a substructural charge density wave (s-CDW) at
T
c
, as well as to a change in configurations of dynamic charge stripes in this metal with electronic instability.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
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.
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.
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