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1.
We show that superexchange interactions in frustrated Jahn-Teller systems with transition metal ions connected by the 90 degrees metal-oxygen-metal bonds (e.g., NaNiO2, LiNiO2, and ZnMn2O4) are much different from those in materials with the 180 degrees bonds. In the 90 degrees -exchange systems spins and orbitals are decoupled: the spin exchange is much weaker than the orbital one and it is ferromagnetic for all orbital states. Though the mean-field orbital ground state is strongly degenerate, quantum orbital fluctuations select particular ferro-orbital states. We explain the orbital and magnetic ordering observed in NaNiO2 and show that LiNiO2 is not a spin-orbital liquid. 相似文献
2.
Kim JH van der Vegte MA Scaramucci A Artyukhin S Chung JH Park S Cheong SW Mostovoy M Lee SH 《Physical review letters》2011,107(9):097401
We studied magnetic excitations in a low-temperature ferroelectric phase of the multiferroic YMn(2)O(5) using inelastic neutron scattering (INS). We identify low-energy magnon modes and establish a correspondence between the magnon peaks observed by INS and electromagnon peaks observed in optical absorption [A. B. Sushkov et al., Phys. Rev. Lett. 98, 027202 (2007).]. Furthermore, we explain the microscopic mechanism, which results in the lowest-energy electromagnon peak, by comparing the inelastic neutron spectral weight with the polarization in the commensurate ferroelectric phase. 相似文献
3.
We study the (spin-)Peierls transition in quasione- dimensional disordered systems, treating the lattice classically. The role of kinks, induced thermally and by disorder, is emphasized. For weak interchain interaction the kinks destroy the coherence between different chains at a temperature significantly lower than the mean-field Peierls transition temperature. We formulate the effective Ising model, which describes such a transition, investigate the doping dependence of the (spin-)Peierls transition temperature and discuss several implications of the picture developed. The results are compared with the properties of the spin-Peierls system CuGeO3. 相似文献
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5.
Mostovoy M 《Physical review letters》2006,96(6):067601
It was recently observed that the ferroelectrics showing the strongest sensitivity to an applied magnetic field are spiral magnets. We present a phenomenological theory of inhomogeneous ferroelectric magnets, which describes their thermodynamics and magnetic field behavior, e.g., dielectric susceptibility anomalies at magnetic transitions and sudden flops of electric polarization in an applied magnetic field. We show that electric polarization can also be induced at domain walls and that magnetic vortices carry electric charge. 相似文献
6.
Presura C Popinciuc M van Loosdrecht PH van der Marel D Mostovoy M Yamauchi T Ueda Y 《Physical review letters》2003,90(2):026402
Temperature dependent optical spectra are reported for beta-Na0.33V2O5. The sodium ordering transition at T(Na)=240 K and, in particular, the charge ordering transition at T(MI)=136 K strongly influence the optical spectra. The metal-insulator transition at T(MI) leads to the opening of a pseudogap ( variant Planck's over 2pi omega=1700 cm(-1)) and to the appearance of a large number of optical phonons. These observations and the presence of a midinfrared band (typical for low dimensional metals) strongly suggest that the charge carriers in beta-Na0.33V2O5 are small polarons. 相似文献
7.
Prokhnenko O Feyerherm R Mostovoy M Aliouane N Dudzik E Wolter AU Maljuk A Argyriou DN 《Physical review letters》2007,99(17):177206
We report on diffraction measurements on multiferroic TbMnO(3) which demonstrate that the Tb- and Mn-magnetic orders are coupled below the ferroelectric transition T(FE) = 28 K. For T相似文献
8.
We study the photonic band structure of cubic crystals of point dipoles. It is shown that in contrast to earlier claims these systems cannot have an omnidirectional photonic band gap. For sufficiently large plasma frequencies, however, they exhibit softening of photonic bands, leading to (anti)ferroelectric ordering of the dipoles and the possibility to open and tune directional band gaps by external electric fields. The model studied may be realized through lattices of quantum dots. 相似文献
9.
M.Yu. Kagan D.I. Khomskii M.V. Mostovoy 《The European Physical Journal B - Condensed Matter and Complex Systems》1999,12(2):217-223
We study the competition between different possible ground states of the double-exchange model with strong ferromagnetic exchange
interaction between itinerant electrons and local spins. Both for classical and quantum treatment of the local spins the homogeneous
canted state is shown to be unstable against a phase separation. The conditions for the phase separation into the mixture
of the antiferromagnetic and ferromagnetic/canted states are given. We also discuss another possible realization of the phase-separated
state: ferromagnetic polarons embedded into an antiferromagnetic surrounding. The general picture of a percolated state, which
emerges from these considerations, is discussed and compared with results of recent experiments on doped manganaties.
Received 17 March 1999 相似文献
10.
We describe the general nonassociative version of Lie theory that relates unital formal multiplications (formal loops), Sabinin algebras and nonassociative bialgebras. 相似文献