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1.
Koichi Itoh Takeji Takui 《Proceedings of the Japan Academy. Series B, Physical and biological sciences》2004,80(2):29
This review paper deals with an overview of molecule-based magnetism as a rapidly developing interdisciplinary field, topological symmetry rule as the first principle of spin alignment in organic open-shell systems in the ground state, the proposal of organic through-bond 1D and 2D ferro- and superparamagnets and the detection of the first organic high-spin molecule, m-phenylenebis(phenylmethylene) in the quintet ground state (S = 2), followed by extended organic high-spin systems with π-conjugation such as aromatic hydrocarbons having S = 3, 4, 5. The paper also describes a theoretical approach to the understanding of electronic spin structures of organic high-spin molecules by invoking both Heisenberg and Hubbard model Hamiltonians, weakly interacting intramolecular high-spin systems from both experimental and theoretical sides, the spin density distribution of the first organic high-spin molecule in terms of electron- nuclear multiple resonance spectroscopy and the detection and characterization of ionic high-spin hydrocarbons, emphasizing the establishment of high spin chemistry underlying organic molecular magnetism. 相似文献
2.
For a class of classical spin models in 2D satisfying a certain continuity constraint it is proven that some of their correlations do not decay exponentially. The class contains discrete and continuous spin systems with Abelian and non-Abelian symmetry groups. For the discrete models our results imply that they show either long-range order or are in a soft phase characterized by powerlike decay of correlations; for the continuous models only the second possibility exists. The continuous models include a version of the plane rotator [O(2)] model; for this model we rederive, modulo two conjectures, the Fröhlich-Spencer result on the existence of the Kosterlitz-Thouless phase in a very simple way. The proof is based on percolation-theoretic and topological arguments. 相似文献
3.
V. V. Semenov N. F. Cherepennikova A. N. Kornev E. V. Naamova N. P. Makarenko S. Ya. Xhorshev G. A. Domrachev O. A. Bochkova 《Russian Chemical Bulletin》1996,45(10):2431-2437
Oligo(phenylcobaltcarbonylsilane) was prepared from oligo(phenylsilane) and dicobalt octacarbonyl. The reaction proceeds with elimination of H2 and CO and insertion of cobalt carbonyl fragments into the silicone backbone of oligosilane. Oligosilane containing cobalt carbonyl groups in side organic substituents was obtained from oligolmethyl(phenylethynyl)Isilane and CO2(CO)8. The reaction of 1,2-bis(phenylethyny1)tetramethyldisilane with Co2(CO)8 proceeds with the sequential attachment of cobalt carbonyl fragments to ethynyl groups to form disilane derivatives [2-CCPhCo2(CO)6] Thermal decomposition of cobalt-containing oligosilanes affords a mixture of paramagnets and ferromagnets.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya. No. 10, pp. 2561–2567, October, 1996. 相似文献
4.
通过第一性原理计算,优化了铁磁性过渡离子掺杂的纤锌矿相硫化锌Fm0.125Zn0.875S(Fm=Fe、Co、Ni)的几何结构,计算了其电子结构,分析了其半金属性及其微观机制。结果表明:对不同的铁磁性杂质离子,Fm0.125Zn0.875S在费米面处的自旋极化率均为-100%,具有半金属性,是潜在的优质自旋注入材料。Fm0.125Zn0.875S具有较宽的自旋带隙,从而具有较高的居里温度和广泛的应用前景。Fe0.125Zn0.875S、Co0.125Zn0.875S和Ni0.125Zn0.875S的2×2×1超胞的磁矩分别为3.96μB、2.90μB和2.00μB,主要来自于铁磁性过渡离子Fe、Co和Ni离子。这3种离子的电子结构分别为eg2↑eg1↓t2g3↑,eg2↑eg2↓t2g3↑和eg2↑eg2↓t2g3↑t2g1↓。 相似文献
5.
Joel L. Lebowitz 《Journal of statistical physics》1977,16(6):463-476
We derive a new inequality for ferromagnetic Ising spin systems and then use it to obtain information about the number of phases which can coexist in such systems. We show in particular that for even interactions only two phases (up and down magnetization) can coexist below the critical temperature at zero magnetic field (h=0) whenever the energy is a continuous function of the temperature. We also prove that the derivatives with respect toh ath=0 of the odd correlation functions (triplet,...) diverge like the susceptibility in the vicinity of the critical temperature (at least for pair interactions). Our results also apply to higher order Ising spins (not just spin 1/2).Research supported in part by NSF Grant #MPS 75-20638 and USAFOR Grant #73-2430D.John Simon Guggenheim Fellow. 相似文献
6.
We prove analyticity properties of correlation functions using correlation inequalities. 相似文献
7.
Co2FeAl0.5Si0.5 (CFAS)-based multilayers sandwiched by MgO layers have been deposited and annealed at different temperatures. Perpendicular magnetic anisotropy (PMA) with the magnetic anisotropy energy density Ku ≈2.5×106 erg/cm3 (1 erg = 10-7 J) and the coercivity Hc = 363 Oe (1 Oe = 79.9775 A · m-1) has been achieved in the Si/SiO2/MgO (1.5 nm)/CFAS (2.5 nm)/MgO (0.8 nm)/Pt (5 nm) film annealed at 300 ℃. The strong PMA is mainly due to the top MgO layer. The structure can be used as top magnetic electrodes in half-metallic perpendicular magnetic tunnel junctions. 相似文献
8.
REN Ji-Rong WANG Ji-Biao LI Ran XU Dong-Hui DUAN Yi-Shi 《理论物理通讯》2008,50(9):777-780
Two kinds of topological soliton (skyrmion and magnetic vortex ring) in ferromagnets are studied. They have the common topological origin, a tensor Hαβ = n→·(δαn→×βδn→), which describes the non-trivial distribution of local orientation of magnetization n→ at large distances in space. The topological stability of skyrmion is protected by the winding number. Knot-like topological defect as magnetic vortex rings is also studied. On the assumption that magnetic vortex rings are geometric lines, we present their δ-function distribution in ferromagnetic materials. Furthermore, it is briefly shown that Hopf invariant is a proper topological invariant to describe the topology of magnetic vortex rings. 相似文献
9.
In this paper, the magnetic and transport properties of the Ti
x
Nb1 − x
CoSn solid solution compounds with half Heusler cubic MgAgAs-type structure have been studied. This work shows the onset of
ferromagnetism associated with a semiconductor to metal transition. The transition occurs directly from ferromagnetic metal
to semiconducting state as it is the case in the TiCo
x
Ni1 − x
Sn series studied previously. A weak quantity of Ti in NbCoSn is suffcient to allow the appearance of ferromagnetic order
and metallic state. The variations of the Curie temperature as a function of saturation and effective paramagnetic moments
are related to the itinerant ferromagnetism model. A comparison is made with the TiCoSn
x
Sb1 − x
series (also studied previously), where the transition from TiCoSn ferromagnetic metal to non-magnetic semiconductor TiCoSb
occurs through an intermediate metallic Pauli-like state.
相似文献
10.
The existence and properties of intrinsic localized spin-wave modes in a ferromagnetic XXZ spin chain with Dzyaloshinsky-Moriya interaction are investigated analytically in the semiclassical limit. The model Hamiltonian is quantized by introducing the Dyson-Maleev transformation and the coherent state representation is chosen as the basic representation of the system. By making use of the method of multiple scales combined with a quasidiscreteness approximation, the equation of motion for the coherent-state amplitude is reduced to the nonlinear Schrödinger equation. It is shown that a bright intrinsic localized spin-wave mode whose eigenfrequency lies below the bottom of the magnon frequency band can exist in the ferromagnetic system. We also show that the system can produce a dark intrinsic localized spin-wave mode, i.e., nonpropagating kink, whose eigenfrequency is below the upper of the magnon frequency band. In addition, we find that the introduction of the Dzyaloshinsky-Moriya interaction changes wave numbers in the Brillouin-zone corresponding to the appearance of intrinsic localized spin-wave modes. 相似文献