Quasiperiodic Solutions of the Heisenberg Ferromagnet Hierarchy

We present quasi-periodic solutions in terms of Riemann theta functions of the Heisenberg ferromagnet hierarchy by using algebro-geometric method. Our main tools include algebraic curve and Riemann surface, polynomial recursive formulation and a special meromorphic function.     

Spontaneous magnetization of randomly dilute ferromagnets

We consider Ising ferromagnets on random subgraphs of the square lattice. These are obtained by independent random selections either of sites or of bonds. We assume that for each site (or, respectively, bond) the probability of being selected exceeds the critical percolation probability. Then, at sufficiently low temperatures and zero external field, spontaneous magnetization occurs. Some further related results are obtained.     

Size dependence of phase transition temperatures of ferromagnetic ,ferroelectric and superconductive nanocrystals

With the miniaturization of devices, size and interface effects become increasingly important for the properties and performances of nanomaterials. Here, we present a thermodynamic approach to the mechanism behind size-induced unusual behavior in the phase stabilities of ferromagnetic (FM), antiferromagnetic (AFM), ferroelectric (FE), and superconductive (SC) nanocrystals, which are different dramatically from their bulk counterparts. This method is based on the Lindemann criterion for melting, Mott’s expression for the vibrational melting entropy, and the Shi model for the size-dependent melting temperature. Simple and unified functions, without any adjustable parameter, are established for the size and interface dependences of thermal and phase stabilities of FM, AFM, FE and SC nanocrystals. According to these analytic functions, as the size of nanocrystals is reduced, the thermal and phase stabilities may strengthen or weaken, depending on the confluence of the surface/volume ratio of nanocrystals and the FM(AFM, FE or SC)/substrate interface situations. The validity of this model is confirmed by a large number of experimental results. This theory will be significant for the choice of materials and the design of devices for practical application.      

Domain wall structure of weak ferromagnets according to Raman

Visualizing the domain structure and the fine structure of domain walls in orthoferrites based on Raman was proposed. The Raman mapping imaging was obtained for the straight and curved domain wall at line 221 cm⁻¹. The parameters of the domain structure and wall obtained by Raman are consistent with magnetooptical measurements.     

铁磁-超导隧道结中的散粒噪声

考虑到铁磁层中的自旋极化效应与粗糙界面散射效应,利用散射理论,讨论铁磁超导隧道结中的散粒噪声.计算表明:磁交换作用可以抑制隧道结系统的平均电流与散粒噪声功率,而粗糙界面散射可以增强系统的平均电流与散粒噪声功率 关键词： 铁磁 超导 隧道结 散粒噪声     

Modified Heisenberg Ferromagnet Model and Integrable Equation

We investigate some integrable modified Heisenberg ferromagnet models by using the prolongation structure theory. Through associating them with the motion of curve in Minkowski space, the corresponding coupled integrable equations are presented.     

Theoretical Investigation of Muon and Muonium Trapping and Hyperfine Interactions in the Chemical Ferromagnet p-NPNN (β-phase)

The trapping sites for muon and muonium in β-phase ferromagnetic p-NPNN have been determined by the first-principles Unrestricted Hartree–Fock procedure. Four trapping sites are found for the muon near the two nitrogen and two oxygen atoms of the two NO groups. For the singlet state of trapped muonium, two trapping sites are found near the two oxygens of two NO groups and for the triplet state two trapping sites are found near the two oxygens of the NO₂ group. The observed μSR signal at zero field with frequency 2.1 MHz is assigned to the singlet muonium sites near the two oxygens of the two NO groups and the high frequency signal ascribed to an isotropic hyperfine constant of 400 MHz is assigned to the two trapped muon sites near the two nitrogen atoms of the two NO groups. This revised version was published online in September 2006 with corrections to the Cover Date.     

Zero-energy bound states in superconductor/ferromagnet superlattices

Andreev bound states in monoatomic superconductor–ferromagnet (S/F) superlattices are studied theoretically, assuming tunneling between S and F layers in perpendicular direction. Andreev reflection at S/F interfaces is strongly affected by the exchange interaction h in F layers. In the ground state, only for h≠0 zero-energy states (ZES) are formed on S and F layers. For h=0, corresponding to superconductor–normal metal (S/N) superlattices, ZES may appear in the nonequilibrium phase, =π. This is found both for s-wave and d-wave symmetry of the order parameter in S. The conditions for ZES are obtained as a function of h, of the transfer integral t for movement of quasiparticles (QPs) between S and F layers, and of the corresponding ground state phase difference _eq between two neighboring S layers.     

Magnon Blockade and Magnon–Atom Entanglement Induced by a Qutrit Coupled to a Ferromagnetic YIG Sphere

Hybridized magnonic–photonic systems promise novel applications for future information processing technologies. Here, a hybrid magnonic system comprising of a qutrit (Λ-type three-level atom) and a ferromagnetic YIG sphere is considered. Indeed, the whole system is driven by two light fields under the influence of the thermal environment. The indirect magnon–atom interaction is established via the virtual photon exchange. The associated Lindblad master equation is derived and its solution is found to investigate the nonclassical feature, especially in the steady-state solution. Generally, the system shows considerable nonclassicality, that is, strong magnon antibunching and magnon blockade. In fact, the feasibility of using such a hybrid system to prepare a single-magnon source based on magnon blockade effects we theoretically demonstrated. Besides, the considered system may be exploited to generate robust and stable magnon–atom entanglement. The appearance of magnon blockade and magnon–atom entanglement in the Λ-type atom may have its origin in the fact that the atom is trapped in different superposition states, induced by the quantum interference phenomenon. The proposed model and the corresponding results may open up an intriguing prospect to prepare a single-magnon source and provide further benefits through concatenating with photons in optomagnonic systems.