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Search Results: 1 - 10 of 256492 matches for " N. Yu. Shitsevalova "
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Surface superconducting states in yttrium hexaboride single crystal in a tilted magnetic field
M. I. Tsindlekht,V. M. Genkin,G. I. Leviev,N. Yu. Shitsevalova
Physics , 2009, DOI: 10.1088/0953-8984/22/9/095701
Abstract: We present the results of an experimental study of the nucleation of superconductivity at the surface of a single crystal YB$_6$ in a tilted dc magnetic field. A recently developed experimental technique allowed us to determine $H_{c3}$ at each side of the sample as a function of the angle between the dc magnetic field and the surface. Experiment shows that the ratio $H_{c3}/ H_{c2}\approx 1.28 $ in the direction perpendicular to the surface dc field while according to the theory this ratio should be equal to 1. This sharp distinction cannot be ascribed to the surface roughness.
Antiferro-quadrupole resonance in CeB6
S. V. Demishev,A. V. Semeno,A. V. Bogach,Yu. B. Paderno,N. Yu. Shitsevalova,N. E. Sluchanko
Physics , 2005, DOI: 10.1016/j.physb.2006.01.160
Abstract: We report experimental observation of a new type of magnetic resonance caused by orbital ordering in a strongly correlated electronic system. Cavity measurements performed on CeB6 single crystals in a frequency range 60-100 GHz show that a crossing of the phase boundary TQ(B) between the antiferro-quadrupole and paramagnetic phases gives rise to development at T
Magnetic resonance in cerium hexaboride caused by quadrupolar ordering
S. V. Demishev,A. V. Semeno,A. V. Bogach,Yu. B. Paderno,N. Yu. Shitsevalova,N. E. Sluchanko
Physics , 2005, DOI: 10.1016/j.jmmm.2005.10.209
Abstract: Experimental evidence of the magnetic resonance in the antiferro-quadrupole phase of CeB6 is reported. We have shown that below orbital ordering temperature a new magnetic contribution from localized magnetic moments (LMM) emerge and gives rise to observed resonant phenomenon. This behaviour is hardly possible to expect in dense Kondo system, where LMM should vanish al low temperatures rather than emerge. From the other hand, in the quadrupole ordering concept, where magnetism of Ce magnetic ions is solely accounted, is difficult to explain splitting of magnetisation into components having different physical nature. Therefore an adequate theory explaining magnetic properties of CeB6 including magnetic resonance and orbital ordering appears on the agenda.
High frequency study of the orbital ordering resonance in the strongly correlated heavy fermion metal CeB6
S. V. Demishev,A. V. Semeno,H. Ohta,S. Okubo,Yu. B. Paderno,N. Yu. Shitsevalova,N. E. Sluchanko
Physics , 2006,
Abstract: We report results of the study of the recently discovered magnetic resonance in the orbitally ordered phase of CeB6 (the orbital ordering resonance) in a wide frequency range 44-360 GHz. It is found that the g-factor for this resonance increases with frequency from g(44 GHz)~1.55 to g(>250 GHz)~1.7. In addition to the orbital ordering resonance for the frequencies exceeding 200 GHz a new magnetic resonance with the g-factor 1.2-1.3 is detected.
Intense low-energy ferromagnetic fluctuations in the antiferromagnetic heavy-fermion metal CeB6
H. Jang,G. Friemel,J. Ollivier,A. V. Dukhnenko,N. Yu. Shitsevalova,V. B. Filipov,B. Keimer,D. S. Inosov
Physics , 2013, DOI: 10.1038/nmat3976
Abstract: Heavy-fermion metals exhibit a plethora of low-temperature ordering phenomena, among them the so-called hidden-order phases that in contrast to conventional magnetic order are invisible to standard neutron diffraction. One of the oldest and structurally simplest hidden-order compounds, CeB6, became famous for an elusive phase that was attributed to the antiferroquadrupolar ordering of cerium-4f moments. In its ground state, CeB6 also develops a more usual antiferromagnetic (AFM) order. Hence, its essential low-temperature physics was always considered to be solely governed by AFM interactions between the dipolar and multipolar Ce moments. Here we overturn this established perspective by uncovering an intense ferromagnetic (FM) low-energy collective mode that dominates the magnetic excitation spectrum of CeB6. Our inelastic neutron-scattering data reveal that the intensity of this FM excitation by far exceeds that of conventional spin-wave magnons emanating from the AFM wave vectors, thus placing CeB6 much closer to a FM instability than could be anticipated. This propensity of CeB6 to ferromagnetism may account for much of its unexplained behavior, such as the existence of a pronounced electron spin resonance, and should lead to a substantial revision of existing theories that have so far largely neglected the role of FM interactions.
On the problem of the Kondo-lattice model application to CeB6
N. E. Sluchanko,A. V. Bogach,V. V. Glushkov,S. V. Demishev,M. I. Ignatov,Yu. B. Paderno,N. A. Samarin,N. Yu. Shitsevalova
Physics , 2005,
Abstract: Precision measurements of charge transport parameters (resistivity, Hall and Seebeck coefficients) have been carried out on high-quality single-crystals of cerium hexaboride in a wide temperature range 1.8-300 K. It is shown that in the temperature interval of 5 K < T < T* = 80 K the magnetic contribution in resistivity obeys the power law rm = T -1/n, which corresponds to the regime of weak localization of charge carriers with the critical index 1/n = 0.39 +- 0.02. In the same temperature interval an asymptotic behavior of thermopower S = -lnT is found together with an essential decrease of the charge carriers mobility in CeB6. A negative Hall coefficient anomaly has been detected at liquid helium temperatures. The data obtained are compared with the results predicted by the Kondo-lattice model and discussed also in terms of the theory of excitonic ferromagnetism.
Hall effect in PrB$_6$ and NdB$_6$
M. A. Anisimov,A. V. Bogach,V. V. Glushkov,S. V. Demishev,N. A. Samarin,V. B. Filipov,N. Yu. Shitsevalova,N. E. Sluchanko
Physics , 2010,
Abstract: Hall effect was studied on the single crystals of antiferromagnets PrB$_6$ and NdB$_6$ at temperatures 2K$<$T$<300$K in magnetic fields up to 8T using the sample rotation technique. At low magnetic fields $\mu_0$H$\leq1$T Hall coefficient R$_\mathrm{H}$, which is practically temperature independent in paramagnetic state at 8K$\leq$T$\leq70$K, is characterized by the values of R$_H$(PrB$_6$)$\sim-(4.2\pm0.1)\cdot10^{-4}$ cm$^3$/C and R$_H$(NdB$_6$)$\sim-(4.1\pm0.1)\cdot10^{-4}$ cm$^3$/C. Rather different behaviour of R$_H$ is observed in antiferromagnetic (AF) phases of these hexaborides. For PrB$_6$ the decrease of temperature below T$_N\approx6.7$K is accompanied by a noticeable ($\Delta R_H/R_H\sim10%$) elevation of R$_H$($\mu_0$H$=1$T) to the values of $-(3.8\pm0.1)\cdot10^{-4}$ cm$^3$/C. On the contrary, the low field Hall coefficient in NdB$_6$ diminishes by about 15% reaching the value R$_H\approx-(4.7\pm0.1)\cdot10^{-4}$ cm$^3$/C in AF state at 2.5K. The increase of magnetic field inducing magnetic transition in the commensurate magnetic phase of PrB$_6$ results in essential R$_H$ changes (up to 10%) at liquid helium temperatures. The anomalous behaviour of the charge transport parameters for RB$_6$ (R=Pr, Nd) found in vicinity of Neel temperature suggests the possible effect of $5d$-states spin density polarization of both in AF and paramagnetic states of the compounds under investigation.
Resonant magnetic exciton mode in the heavy-fermion antiferromagnet CeB6
G. Friemel,Yuan Li,A. V. Dukhnenko,N. Yu. Shitsevalova,N. E. Sluchanko,A. Ivanov,V. B. Filipov,B. Keimer,D. S. Inosov
Physics , 2011, DOI: 10.1038/ncomms1821
Abstract: Resonant magnetic excitations are widely recognized as hallmarks of unconventional superconductivity in copper oxides, iron pnictides, and heavy-fermion compounds. Numerous model calculations have related these modes to the microscopic properties of the pair wave function, but the mechanisms underlying their formation are still debated. Here we report the discovery of a similar resonant mode in the non-superconducting, antiferromagnetically ordered heavy-fermion metal CeB6. Unlike conventional magnons, the mode is non-dispersive, and its intensity is sharply concentrated around a wave vector separate from those characterizing the antiferromagnetic order. The magnetic intensity distribution rather suggests that the mode is associated with a coexisting order parameter of the unusual antiferro-quadrupolar phase of CeB6, which has long remained "hidden" to the neutron-scattering probes. The mode energy increases continuously below the onset temperature for antiferromagnetism, in parallel to the opening of a nearly isotropic spin gap throughout the Brillouin zone. These attributes bear strong similarity to those of the resonant modes observed in unconventional superconductors below their critical temperatures. This unexpected commonality between the two disparate ground states indicates the dominance of itinerant spin dynamics in the ordered low-temperature phases of CeB6 and throws new light on the interplay between antiferromagnetism, superconductivity, and "hidden" order parameters in correlated-electron materials.
Superconductivity mediated by a soft phonon mode: specific heat, resistivity, thermal expansion and magnetization of YB6
R. Lortz,Y. Wang,U. Tutsch,S. Abe,C. Meingast,P. Popovich,W. Knafo,N. Shitsevalova,Yu. B. Paderno,A. Junod
Physics , 2005, DOI: 10.1103/PhysRevB.73.024512
Abstract: The superconductor YB6 has the second highest critical temperature Tc among the boride family MBn. We report measurements of the specific heat, resistivity, magnetic susceptibility and thermal expansion from 2 to 300 K, using a single crystal with Tc = 7.2 K. The superconducting gap is characteristic of medium-strong coupling. The specific heat, resistivity and expansivity curves are deconvolved to yield approximations of the phonon density of states, the spectral electron-phonon scattering function and the phonon density of states weighted by the frequency-dependent Grueneisen parameter respectively. Lattice vibrations extend to high frequencies >100 meV, but a dominant Einstein-like mode at ~8 meV, associated with the vibrations of yttrium ions in oversized boron cages, appears to provide most of the superconducting coupling and gives rise to an unusual temperature behavior of several observable quantities. A surface critical field Hc3 is also observed.
Yb-Yb correlations and crystal-field effects in the Kondo insulator YbB12 and its solid solutions
P. A. Alekseev,J. -M. Mignot,K. S. Nemkovski,E. V. Nefeodova,N. Yu. Shitsevalova,Yu. B. Paderno,R. I. Bewley,R. S. Eccleston,E. S. Clementyev,V. N. Lazukov,I. P. Sadikov,N. N. Tiden
Physics , 2003, DOI: 10.1088/0953-8984/16/15/015
Abstract: We have studied the effect of Lu substitution on the spin dynamics of the Kondo insulator YbB12 to clarify the origin of the spin-gap response previously observed at low temperature in this material. Inelastic neutron spectra have been measured in Yb1-xLuxB12 compounds for four Lu concentrations x = 0, 0.25, 0.90 and 1.0. The data indicate that the disruption of coherence on the Yb sublattice primarily affects the narrow peak structure occurring near 15-20 meV in pure YbB12, whereas the spin gap and the broad magnetic signal around 38 meV remain almost unaffected. It is inferred that the latter features reflect mainly local, single-site processes, and may be reminiscent of the inelastic magnetic response reported for mixed-valence intermetallic compounds. On the other hand, the lower component at 15 meV is most likely due to dynamic short-range magnetic correlations. The crystal-field splitting in YbB12 estimated from the Er3+ transitions measured in a Yb0.9Er0.1B12 sample, has the same order of magnitude as other relevant energy scales of the system and is thus likely to play a role in the form of the magnetic spectral response.
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