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STUDIES ON THE NEXT-NEAREST NEIGHBOR HOPPING INTERACTIONS OF π-ELECTRONS IN QUASI-ONE-DIMENSIONAL ORGANIC FERROMAGNETIC MODEL
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Based on a theoretical model proposed for quasi-one-dimensional organic polymer fer-romagnets, the next-nearest neighbor hopping interactions of sr-electrons are considered. Allowing for full lattice relaxation, a set of self-consistent equations is established to study the system. The spin-density-wave (SDW) and the possible ferromagnetic ground state of the system are investigated in detail. It is found that the next-nearest neighbor hopping in-teractions will make the SDW stronger and consequently make the ferromagnetic state more stable as compared with the nonmagnetic reference state. 相似文献
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The two-dimensional, colossal magnetoresistive system GdI2 develops an unusual metallic state below its ferromagnetic transition and becomes insulating at low temperatures. We argue that this geometrically frustrated, correlated poor metal is a possible candidate for a ferromagnetic excitonic liquid. The renormalized Fermi surface supports a further breaking of symmetry to a charge-ordered, excitonic solid ground state at lower temperatures via order by disorder mechanism. Several experimental predictions are made to investigate this unique orbitally correlated ground state. 相似文献
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用有限元方法近似计算了1s2p态氦原子单态和三重态的能量,所得结果的相对误差:三重态为10-6,单态为10-4.这一结果比Schertzer[1]对基态氦原子的相应结果稍好.有限元法导致的大型广义矩阵特征值问题,对于基态是对称的,而对于1s2p态是非对称的,给求解带来了难度.由波函数的图形说明,在有界区域上求Schrödinger方程的近似解是合理的. 相似文献
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K.L. Yao L. Zhao 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(3):411-417
Based on a theoretical model proposed for quasi-one-dimensional organic polymer ferromagnets, the ground state and low-lying
magnetic excitation are studied. Within Hartree-Fock approximation, the ground state of the system is shown to be a stable
ferromagnetic state due to the electron-electron correlation and topological structure of the system. The random-phase approximation
is employed to explore the magnon excitation and the excitation spectrum is obtained, including an acoustic mode and four
optical modes. It is found that the acoustic mode possesses the characteristic of the ferromagnetic magnon.
Received 9 July 1999 相似文献
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E. Z. Meilikhov R. M. Farzetdinova 《Journal of Experimental and Theoretical Physics》2002,94(4):751-758
The magnetic phase diagrams of 2D and 3D regular lattices formed by nonspherical single-domain ferromagnetic granules featuring a dipolar magnetic interaction are studied. The energy of a magnetic state of such systems is calculated using an approximate expression for the pair interaction of nonspherical granules. The character of the magnetic ground state of the system is determined by three geometric parameters: (i) the eccentricity of granules; (ii) the ratio of periods of the rectangular (2D) or tetragonal (3D) lattice; and (iii) the ratio of a lattice period to a granule size. In contrast to the case of lattices formed by point (or spherical) magnetic moments, in which the ground state is always antiferromagnetic or frustrated (for triangular lattices), the ground state of a 2D lattice composed of nonspherical granules can be ferromagnetic. The magnetic phase diagrams of the systems studied are constructed in the space of the above geometric parameters. 相似文献
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D. Gao A. K. Ray 《The European Physical Journal B - Condensed Matter and Complex Systems》2007,55(1):13-22
Electronic structures of double hexagonal close-packed americium and the
(0001) surface have been studied via full-potential all-electron
density-functional calculations with a mixed APW+lo/LAPW basis. The
electronic and geometric properties of bulk dhcp Am as well as quantum size
effects in the surface energies and the work functions of the dhcp Am (0001)
ultra thin films up to seven layers have been examined at nonmagnetic,
ferromagnetic, and antiferromagnetic configurations with and without spin
orbit coupling. The anti-ferromagnetic state including spin-orbit coupling
is found to be the ground state of dhcp Am with the 5f electrons primarily
localized. Our results show that both magnetic configurations and spin-orbit
coupling play important roles in determining the equilibrium lattice
constant, the bulk modulus as well as the localized feature of 5f electrons
for dhcp Am. Our calculated equilibrium lattice constant and bulk modulus at
the ground state are in good agreement with the experimental values
respectively. The work function of dhcp Am (0001) 7-layer surface at the
ground state is predicted to be 2.90 eV. The surface energy for dhcp Am
(0001) semi-infinite surface energy at the ground state is predicted to be
0.84 J/m2. Quantum size effects are found to be more pronounced in work
functions than in surface energies. 相似文献
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Chalcopyrite II-IV-V 2 semiconductors CdGeP 2 : Mn and ZnGeP 2 : Mn are new types of diluted magnetic semiconductors (DMSs). Since their ferromagnetic Curie temperatures are much higher than room temperature, these DMSs are good candidates for materials to be used in spintronics devices. Their electronic and magnetic structures have been investigated using the first-principles calculations based on the Korringa-Kohn-Rostoker coherent-potential-approximation and local-density-approximation (KKR-CPA-LDA) methods. When Cd or Zn atoms are substituted by Mn atoms, the ground state magnetic structure is spinglass-like. On the other hand, if Mn atoms substitute Ge atoms, the system becomes ferromagnetic through the double-exchange mechanism. However, the calculation of the formation energies shows that this system is not energetically favorable. Instead, the system with vacancies (Cd, Vc, Mn)GeP 2 or a non-stoichiometric (Cd, Ge, Mn)GeP 2 are also ferromagnetic and, moreover, energetically stable. We conclude that either of these variants possess a ferromagnetic phase of the kind CdGeP 2 : Mn. Similar conclusions are obtained for ZnGeP 2 : Mn. 相似文献
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Bálint Tóth 《Letters in Mathematical Physics》1991,22(4):321-333
We consider the Hubbard model on a finite set of sites with nonpositive hopping matrix elements and infinitely strong on-site repulsion. Nagaoka's theorem states that in this model the relative ground state in the sector with one unoccupied site is maximally ferromagnetic. We show that this phenomenon is a consequence of a combinatorial coincidence valid in the one-hole regime only. In the case of more than one hole there is no reason to expect maximally ferromagnetic ground states. We prove this claim for the case of two holes for models defined on a class of graphs which contains all tori that are not too small. 相似文献
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We investigate the effect of geometry on the ground-state ordering of artificially frustrated magnetic rectangular and triangular lattices by Monte Carlo method. By varying the vertical lattice spacing while keeping the horizontal one fixed, we show that when the ratio of vertical to horizontal lattice spacing, labeled by η, is less than 1.82, the ground state of the rectangular lattice presents long-range antiferromagnetic order and for η?1.82 the ground state changes to long-range mixed ferromagnetic and antiferromagnetic order. For the frustrated triangular lattice, the short-range ordered state as well as two long-range ordered ground states occurs transiently at η=0.87 and 2, where the energies of the two ground states with long-range order are approximately equal. In addition, the level of frustration of both frustrated lattices is found to be largely relevant to the ratio η. 相似文献
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利用平均场理论讨论了零温下具有长程库仑势的电子气体和短程相互作用的费米原子气体的铁磁相变问题,比较了两个模型中铁磁转变的不同性质. 相似文献
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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
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《Physica A》1987,144(1):128-139
A class of possible periodic orientational configurations of a system of dipole moments located at the sites of an infinite flat rhombic lattice with an arbitrary rhombicity angle α is studied by using the Luttinger and Tisza method. In the framework of the method it is obtained that: for α ⪅ 80° the ground state is ferromagnetic, at α = 60° being continuously degenerate in direction; for 80° ⪅ α ⩽ 90° the ground state is antiferromagnetic, at α = 90° being also continuously degenerate with respect to one parameter. It is shown that the restriction of the interaction range leads to a change in the type of the ground state: at α = 60° this takes place between the third and the fourth coordination spheres and at α = 30° at a distance of about 500 lattice constants. From comparison with known results of numerical experiments on finite systems it is established that the type of the ground state of a finite and an infinite system may be essentially different. 相似文献
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We study analytically and by molecular dynamics simulations the ground state configuration of a system of magnetic dipoles fixed on a two-dimensional lattice. We find different phases, in close agreement with previous results. Building on this result and on the minimum energy requirement we determine the equilibrium lattice configuration, the magnetic order (ferromagnetic versus antiferromagnetic), and the magnetic polarization direction of a system of charged mesoscopic particles with magnetic dipole moments, in the domain where the strong electrostatic coupling leads to a crystalline ground state. Orders of magnitudes of the parameters of the system relevant to possible future dusty plasma experiments are discussed. 相似文献
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D.V. Dmitriev V.Ya. Krivnov A.A. Ovchinnikov 《The European Physical Journal B - Condensed Matter and Complex Systems》2000,14(1):91-97
We study the spin ladder model with interactions between spins on neighboring rungs. The model Hamiltonian with the exact
singlet ground state degenerated with ferromagnetic state is obtained. The singlet ground state wave function has a special
recurrent form and depends on two parameters. Spin correlations in the singlet ground state show double-spiral structure with
period of spirals equals to the system size. For special values of parameters they have exponential decay. The spectrum of
the model is gapless and there are asymptotically degenerated excited states for special values of parameters in the thermodynamic
limit.
Received 7 May 1999 相似文献
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K. Schönhammer 《Zeitschrift für Physik B Condensed Matter》1975,21(4):389-392
Starting from the Hartree-Fock approximation a general variational ansatz for the ground state of the metal-hydrogen system is presented which properly describes the strong correlation effects occuring at larger distances from the surface. As a simple example the Anderson model is studied. The calculated ground state energies are in excellent agreement with exact model calculations. 相似文献
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A strong coupling expansion for a two‐band Hubbard model on two sites with nearly degenerate states is considered. A comparative analysis is performed for different schemes of perturbation theory which are applicable to systems with nearly degenerate states. A fourth order approach which builds on a four‐dimensional low‐energy subspace with nearly degenerate states captures accurately the transition from an antiferromagnetic to a ferromagnetic ground state at large on‐site Coulomb interaction. 相似文献