共查询到20条相似文献,搜索用时 15 毫秒
1.
A. Malashevich D. Vanderbilt 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,71(3):345-348
We study the polarization induced via spin-orbit interaction
by a magnetic cycloidal order
in orthorhombic TbMnO3 using first-principle methods. The case
of magnetic spiral lying in the b-c plane is analyzed,
in which the pure electronic contribution to the polarization
is shown to be small. We focus our attention on the lattice-mediated
contribution, and study it’s dependence on the Coulomb interaction
parameter U in the LDA+U method and on the wave-vector of the
spin spiral. The role of the spin-orbit interaction on different sites
is also analyzed. 相似文献
2.
A. I. Lebedev 《Physics of the Solid State》2011,53(12):2463-2467
First-principles density functional theory is used to calculate the phonon spectrum in the paraelectric phase, the ground-state
structure and polarization distribution in the polar phase, and energies of ferro- and antiferroelectrically ordered phases
of free-standing (KNbO3)1(KTaO3)
n
ferroelectric superlattices with n = 1–7. It is established that quasi-two-dimensional ferroelectricity with polarization oriented in the layer plane, which
weakly interacts with polarization in neighboring layers, appears in potassium niobate layers with a thickness of one unit
cell in the superlattices. The possibility of using of such ferroelectric superlattices as a medium for three-dimensional
information recording is shown. 相似文献
3.
M. Schmidt Ch. Kant T. Rudolf F. Mayr A. A. Mukhin A. M. Balbashov J. Deisenhofer A. Loidl 《The European Physical Journal B - Condensed Matter and Complex Systems》2009,71(3):411-418
We provide a detailed study of the reflectivity of multiferroic TbMnO3 for wave numbers from
40 cm-1 to 1000 cm-1 and temperatures 5 K < T < 300 K. Excitations are studied for
polarization directions E || a, the polarization where electromagnons are observed,
and for E || c, the direction of the spontaneous polarization in this material. The
temperature dependencies of eigenfrequencies, damping constants and polar strengths of all modes are studied and
analyzed. For E || a and below the spiral ordering temperature of about 27 K we
observe a transfer of optical weight from phonon excitations to electromagnons, which mainly involves
low-frequency phonons. For E || c an unusual increase of the total polar strength and
hence of the dielectric constant is observed indicating significant transfer of dynamic charge probably within
manganese-oxygen bonds on decreasing temperatures. 相似文献
4.
A phenomenological theory for polarization flop in spiral multiferroic TbMnO<Subscript>3</Subscript>
A phenomenological Landau theory has been used to explain magnetic field-driven polarization flop in TbMnO 3. The Néel wall-like magnetic structure in spiral multiferroics induces a space-dependent internal magnetic field which exerts a torque on spins to rotate bc-spiral to ab-spiral. The external magnetic field is argued to be competing with easy axis anisotropy and the system stabilizes when anisotropy is minimum. With the help of Landau free energy with DM magnetoelectric coupling and a general ansatz for magnetization, the phenomenon of polarization flop has been explained. Relation between Tflop and critical magnetic field has been established and found to be in good agreement with the experiment. This could be an indication that anisotropy of the system is temperature- and magnetic field-dependent. 相似文献
5.
We examine the interplay between quantum charge fluctuations and magnetic ordering in multiferroic LuFe2O4 and show that this can couple spin and charge degrees of freedom in a LuFe2O4 bilayer below the Neel temperature T N . Our analysis supports the idea that the double exchange mechanism normally used in metallic systems can be applied to charge-ordered insulators. This causes ferrimagnetic spin order to reduce the transfer integrals between Fe2+ and Fe3+ in LuFe2O4, decreasing charge fluctuations and increasing the polarization in this system below T N . This work thus provides a more detailed understanding of the mechanism for spin-charge coupling in LuFe2O4. 相似文献
6.
As a single-phase multiferroic material, Fe3O4 exhibits spontaneous ferroelectric polarization below 38 K. However, the nature of the ferroelectricity in Fe3O4 and effect of external disturbances such as strain on it remains ambiguous. Here, the spontaneous ferroelectric polarization of low-temperature monoclinic Fe3O4 was investigated by first-principles calculations. The pseudo-centrosymmetric FeB42–FeB43 pair has a different valence state. The noncentrosymmetric charge distribution results in ferroelectric polarization. The initial ferroelectric polarization direction is in the -x and -z directions. The ferroelectricity along the y axis is limited owing to the symmetry of the Cc space group. Both the ionic displacement and charge separation at the FeB42–FeB43 pair are affected by strain, which further influences the spontaneous ferroelectric polarization of monoclinic Fe3O4. The ferroelectric polarization along the z axis exhibits an increase of 45.3% as the strain changes from 6% to -6%. 相似文献
7.
B. Xu X. Li J. Sun L. Yi 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,66(4):483-487
Using first-principles calculations based on density-functional theory in
its local-density approximation, we investigated the Electronic structure,
ferroelectricity and optical properties of CaBi2Ta2O9 (CBT)
for the first time. It is found that CBT compound has an indirect band gap
of 3.114 eV and the O 2s and 2p states are strongly hybridized with the 6s
states of Bi which belong to the (Bi2O2)2+ planes. The quite
strong Ta–O and Bi–O hybridization is the primary source for
ferroelectricity. Our results imply that the interaction between Bi and O is
highly covalent. The anisotropy occurs mainly above 4 eV in the optical
properties. The different optical properties have been discussed. 相似文献
8.
The spectrum of spin fluctuations in the stacked-triangular antiferromagnet YMnO3 was studied above the Néel temperature using both unpolarized and polarized inelastic neutron scattering. We find an in-plane and an out-of-plane excitation. The in-plane mode has two components just above T N : a resolution-limited central peak and a Debye-like contribution. The quasi-elastic fluctuations have a line width that increases with q as Dq z and the dynamical exponent z = 2.3. The out-of-plane fluctuations have a gap at the magnetic zone center and do not show any appreciable q dependence at small wave vectors. 相似文献
9.
We report X-ray diffraction, magnetization and transport measurements for polycrystalline samples of the new layered superconductor Bi4?x Ag x O4S3(0 ≤ x ≤ 0.2). The superconducting transition temperature (T C) decreases gradually and finally suppressed when x < 0.10. Accordingly, the resistivity changes from a metallic behavior for x < 0.1 to a semiconductor-like behavior for x > 0.1. The analysis of Seebeck coefficient shows there are two types of electron-like carriers dominate at different temperature regions, indicative of a multiband effect responsible for the transport properties. The suppression of superconductivity and the increased resistivity can be attributed to a shift of the Fermi level to the lower-energy side upon doping, which reduces the density of states at E F. Further, our result indicates the superconductivity in Bi4O4S3 is intrinsic and the dopant Ag prefers to enter the BiS2 layers, which may essentially modify the electronic structure. 相似文献
10.
E. I. Pogorel’tsev E. V. Bogdanov M. S. Molokeev V. N. Voronov L. I. Isaenko S. A. Zhurkov N. M. Laptash M. V. Gorev I. N. Flerov 《Physics of the Solid State》2011,53(6):1202-1211
According to the results of calorimetric and structural studies, the Fm{ie1202-1}m phase in K2NaMoO3F3 remains stable at least to 100 K. No ferroelectric transformation assumed earlier has been revealed in a series of Rb2KMoO3F3 samples prepared using various technologies. Only a phase transition of nonferroelectric origin has been observed near 195
K, and its thermodynamic characteristics have been determined. An analysis of the stability of the cubic structure of molybdenum
fluorine-oxygen elpasolites-cryolites has been performed in the framework of the hypothesis on strengths of interatomic bonds.
The barocaloric effect in Rb2KMoO3F3 has been estimated. 相似文献
11.
A. L. Freidman A. A. Dubrovskii V. L. Temerov I. A. Gudim 《Physics of the Solid State》2018,60(3):510-514
The comparative study of the magnetoelectric properties and magnetostriction of HoGa3(BO3)4 and HoAl3(BO3)4 single crystals has been carried out. The investigated compounds exhibit qualitatively similar magnetodielectric and inverse magnetoelectric ME E effects with the close absolute values, which is indicative of the weak effect of a nonmagnetic metal ion. On the contrary, the magnetostriction of the galloborate has been found to be threefold higher than that of the alumoborate. In addition, the difference between the qualitative behaviors of magnetostriction has been established: the magnetic-field dependence of magnetostriction for the alumoborate has the maximum near 70 kOe at T = 4.2 K, while the galloborate magnetostriction has no maximum and does not saturate in a field of 140 kOe. 相似文献
12.
We analyze measurements of the magnetization, differential susceptibility and specific heat of quasi-onedimensional insulator Cu(C4H4N2)(NO3)2 (CuPzN) subjected to magnetic fields. We show that the thermodynamic properties are defined by quantum spin liquid formed with spinons, with the magnetic field tuning the insulator CuPzN towards quantum critical point related to fermion condensation quantum phase transition (FCQPT) at which the spinon effective mass diverges kinematically. We show that the FCQPT concept permits to reveal and explain the scaling behavior of thermodynamic characteristics. For the first time, we construct the schematic T–H (temperature-magnetic field) phase diagram of CuPzN that contains Landau–Fermi-liquid, crossover and non-Fermi liquid parts, thus resembling that of heavy-fermion compounds. 相似文献
13.
14.
Yu. V. Gerasimova A. S. Krylov A. N. Vtyurin A. A. Ivanenko N. P. Shestakov N. M. Laptash 《Bulletin of the Russian Academy of Sciences: Physics》2008,72(8):1145-1148
Comparative analysis of the IR absorption and Raman scattering spectra of a polycrystalline sample of perovskite-type oxyfluoride (NH4)3WO3F3 has been performed in the frequency range 370–4000 cm?1 at temperatures from 92 to 303 K, including the transition between the orientationally disordered cubic and low-symmetry phases. The conformation of WO3F3 octahedral groups is established and transitional anomalies of the internal modes of these groups and ammonium ions are revealed. Comparative analysis of the IR and Raman spectra suggests that the phase transition under study is mainly related to the ordering of octahedral groups and formation of W-O…H-N hydrogen bonds. 相似文献
15.
D. V. Volkov A. A. Demidov N. P. Kolmakova 《Journal of Experimental and Theoretical Physics》2008,106(4):723-730
The magnetic properties of an easy-axis trigonal DyFe3(BO3)4 antiferromagnetic crystal have been theoretically studied. On this basis, recent experimental data [1] on the field and temperature dependences of magnetization and the temperature dependence of the initial magnetic susceptibility for three crystallographic directions in this antiferromagnet have been interpreted. The characteristics of the trigonal crystal field for the rare earth ion and the parameters of the Fe-Fe and Fe-Dy exchange interactions are determined. Limitations imposed by features of the magnetic characteristics (anisotropic magnetization in the three crystallographic directions, Schottky-type anomalies in the magnetic susceptibility, etc.) on the possible splitting of the ground-state multiplet in the crystal field and the splitting of the lowest doublet due to the f-d interaction for Dy3+ ions are established. 相似文献
16.
I. A. Gudim A. A. Demidov E. V. Eremin D. K. Shukla 《Physics of the Solid State》2018,60(10):1989-1998
The magnetic and magnetodielectric properties of Ho0.5Nd0.5Fe3(BO3)4 ferroborate with the competing Ho–Fe and Nd–Fe exchange couplings have been experimentally and theoretically investigated. Step anomalies in the magnetization curves at the spin-reorientation transition induced by the magnetic field B ║ c have been found. The spontaneous spin-reorientation transition temperature TSR ≈ 8 K has been refined. The measured magnetic properties and observed features are interpreted using a single theoretical approach based on the molecular field approximation and calculations within the crystal field model of the rare-earth ion. Interpretation of the experimental data includes determination of the crystal field parameters for Ho3+ and Nd3+ ions in Ho0.5Nd0.5Fe3(BO3)4 and parameters of the Ho–Fe and Nd–Fe exchange couplings. 相似文献
17.
R. Z. Levitin E. A. Popova R. M. Chtsherbov A. N. Vasiliev M. N. Popova E. P. Chukalina S. A. Klimin P. H. M. van Loosdrecht D. Fausti L. N. Bezmaternykh 《JETP Letters》2004,79(9):423-426
Cascade of phase transitions in GdFe3(BO3)4 at 156, 37, and 9 K has been detected by specific heat measurements and further studied by Raman scattering and Nd3+ spectroscopic probe method. A weakly first-order structural phase transition at 156 K is followed by a second-order antiferromagnetic ordering phase transition at 37 K and a first-order spin-reorientational phase transition at 9 K. 相似文献
18.
Thin films of Sb2Te3 and (Sb2Te3)70(Bi2Te3)30 alloy and have been deposited on precleaned glass substrate by thermal evaporation technique in a vacuum of 2?×?10?6 Torr. The structural study was carried out by X-ray diffractometer, which shows that the films are polycrystalline in nature. The grain size, microstrain and dislocation density were determined. The Seebeck coefficient was determined as the ratio of the potential difference across the films to the temperature difference. The power factor for the (Sb2Te3)70 (Bi2Te3)30 and (Sb2Te3) is found to be 19.602 and 1.066 of the film of thickness 1,500 Å, respectively. The Van der-Pauw technique was used to measure the Hall coefficient at room temperature. The carrier concentration was calculated and the results were discussed. 相似文献
19.
T. V. Sviridova L. Yu. Sadovskaya A. I. Kokorin E. A. Konstantinova V. E. Agabekov D. V. Sviridov 《Russian Journal of Physical Chemistry B, Focus on Physics》2017,11(2):348-353
The thin-film photocatalysts TiO2/MoO3 and TiO2/MoO3:V2O5 obtained by a combination of sol–gel and sintering techniques were studied using the photooxidation of probing dyes, EPR spectroscopy, X-ray diffraction analysis, and electron microscopy. It was shown that due to charge accumulation caused by UV irradiation, these photocatalysts retain their oxidative activity and ability for self-sterilization in the dark for a long time after irradiation was terminated (up to 5 h for TiO2/MoO3:V2O5). 相似文献
20.
We report transport, magnetic and thermodynamic properties of the
skutterudite compound LaFe4Sb12. The basic features are a large
magnetic susceptibility χ(T), and large electronic coefficient
γ of the heat capacity. In particular, a T1.35, T1.7, and
T-2/3 temperature dependence of the magnetic susceptibility χ(T),
resistivity ρ(T), and Grüneisen parameter Γ(T), respectively, is found at low temperature. An overall understanding of these physical properties is achieved, assuming that
LaFe4Sb12 is a non-Fermi liquid system close to a ferromagnetic quantum critical point, with a spin fluctuation temperature Tsf=50±15 K. 相似文献