On the anatomy of multi-spin magnon and single spike string solutions

We study rigid string solutions rotating in AdS₅×S⁵${\mathit{AdS}}_5\times S^5$ background. For particular values of the parameters of the solutions we find multispin solutions corresponding to giant magnons and single spike strings. We present an analysis of the dispersion relations in the case of three spin solutions distributed only in S⁵$S^5$ and the case of one spin in AdS₅${\mathit{AdS}}_5$ and two spins in S⁵$S^5$. The possible relation of these string solutions to gauge theory operators and spin chains are briefly discussed.     

Effect of Co layer thickness on the magnetic properties of Tb30Co70/SiNx/Co thin films

The SiN_x (20 nm)/Tb₃₀Co₇₀ (90 nm)/SiN_x (5 nm)/Co (3–37 nm)/SiN_x (10 nm)/Si multilayer films are deposited on naturally oxidized Si wafer by magnetron sputtering. The saturation magnetization (M_s) of the multilayer films is increased with the thickness of high M_s ferromagnetic Co layer. The perpendicular coercivity (_Hc⊥$H_{{\mathrm{c}}^{\perp }}$) value is increased with Co layer thickness as the thickness of the Co layer is lower than 15 nm and then decreases drastically when the thickness of the Co layer further increased. The increase of the _Hc⊥$H_{{\mathrm{c}}^{\perp }}$ value is owing to the interlayer exchange effect [Li Zhang, Physica B 390 (2007) 373] between TbCo and Co layers. Co under-layer with in-plane magnetic anisotropy would pin the magnetic moment of the TbCo layer near by the Co layer and cause the value of _Hc⊥$H_{{\mathrm{c}}^{\perp }}$ to increase. However, as the Co layer is thicker than a critical thickness, the _Hc⊥$H_{{\mathrm{c}}^{\perp }}$ value of the multilayer film would decrease. Therefore, the Co layer with in-plane magnetic anisotropy and soft magnetic properties is expected to dominate the magnetic properties of the multilayer films.     

The phase diagram of a ferrimagnetic multilayer system with disordered interface layers

The critical and compensation behaviors of a ferrimagnetic multilayer system on a simple cubic structure consisting of L layer of spin-1/2 A atoms, L   layers of spin-1 B atoms and a disordered interface with two layers in between that is characterized by a random arrangement of A and B atoms of _APB1-P${\mathrm{A}}_P{\mathrm{B}}_{1-P}$ type in the first layer and _A1-PBP${\mathrm{A}}_{1-P}{\mathrm{B}}_P$ type in the second layer and a negative A–B coupling, are examined using the effective field theory based on a probability distribution technique. The effect of the probability p$p$, interactions, different anisotropy and the thickness L on the magnetic properties is examined. The obtained results show a number of characteristic features, such as the possibility of many compensation points.     

The quantum correlation of anisotropic Heisenberg spin chain under the control of inhomogeneous magnetic field

The quantum correlation (quantum entanglement and quantum discord)’s dynamical behavior characteristics of Heisenberg XXZ spin chain with Dzyaloshinskii–Moriya (DM) interaction heterogeneous magnetic field that manipulated by sinusoidal wave are investigated in this paper. The results indicate that quantum correlation of anisotropic Heisenberg XXZ spin chain can be regulated effectively by magnetic field intensity B and magnetic field uniformity cos θ   of the external magnetic field. Under the effects of DM interaction in qubits, the quantum correlation's dynamics evolution process appears sudden death and birth. But DM interaction has a critical value D_CZ$D_{CZ}$ which is connected with other quantum correlation versus parameters. Only when Dz≥D_CZ$D_z\ge D_{CZ}$, sudden death and birth can be obviously observed under the rest given parameters.     

Magnetic linear dichroism studies of in situ grown NiO thin films

We report thickness dependence of magnetic linear dichroism (MLD) of in situ grown NiO(0 0 1) films on Ag(0 0 1) substrate at the Ni L₂ absorption edge. Antiferromagnetic domains at the surface of NiO(0 0 1) films are found to be preferentially aligned in-plane. For films thinner than a critical thickness _tc$t_{\mathrm{c}}$ (20–40ML), we observe a softening of the in-plane magnetic domain alignments with increasing film thickness, arising from the strain-relaxation effects. Films thicker than _tc$t_{\mathrm{c}}$ exhibits a residual in-plane anisotropy, possibly related to the finite-thickness effects.     

Thermodynamics of antiferromagnetic alternating spin chains

We consider integrable quantum spin chains with alternating spins (S₁,S₂)$(S_1,S_2)$. We derive a finite set of non-linear integral equations for the thermodynamics of these models by use of the quantum transfer matrix approach. Numerical solutions of the integral equations are provided for quantities like specific heat, magnetic susceptibility and in the case S₁=S₂$S_1=S_2$ for the thermal Drude weight. At low temperatures one class of models shows finite magnetization and the other class presents antiferromagnetic behaviour. The thermal Drude weight behaves linearly on T at low temperatures and is proportional to the central charge c   of the system. Quite generally, we observe residual entropy for S₁≠S₂$S_1\ne S_2$.     

The spin-ladder and spin-chain system (La,Y,Sr,Ca)14Cu24O41: Electronic phases,charge and spin dynamics

The quasi-one-dimensional cuprates (La,Y,Sr,Ca)₁₄Cu₂₄O₄₁, consisting of spin-chains and spin-ladders, have attracted much attention, mainly because they represent the first superconducting copper oxide with a non-square lattice. Theoretically, in isolated hole-doped two-leg ladders, superconductivity is tightly associated with the spin gap, although in competition with a charge-density wave (CDW). Indeed, both the gapped spin-liquid and CDW states have been established in the doped spin-ladders of _{Sr14-xCaxCu24O41}${\mathrm{Sr}}_{14-x}{\mathrm{Ca}}_x{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$, however the relevance of these objects to electronic properties and superconductivity is still subject of intensive discussion. In this treatise, an appreciable set of experimental data is reviewed, which has been acquired in recent years, indicating a variety of magnetic and charge arrangements found in the chains and ladders of underdoped (La,Y)_y(S,Ca)_14−yCu₂₄O₄₁ and fully doped _{Sr14-xCaxCu24O41}${\mathrm{Sr}}_{14-x}{\mathrm{Ca}}_x{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$. Based on these data, phase diagrams are constructed for the chains of underdoped systems (as a function of La, Y-substitution), as well as for the chains and ladders of the fully doped ones (as a function of Ca-substitution). We try to reconcile contradictory results concerning the charge dynamics in the ladders, like the hole redistribution between ladders and chains, collective modes and pseudogap, field-dependent transport and the temperature scales and doping levels at which the two-dimensional CDW develops in the ladder planes. The remaining open issues are clearly extracted. In the discussion the experimental results are contrasted with theoretical predictions, which allows us to conclude with two important remarks concerning the nature of the competing CDW and superconducting ground states. A density wave in ladders, characterized by a sinusoidal charge modulation, belongs to the class of broken symmetry patterns, which is theoretically predicted for strongly correlated low-dimensional electron systems; however its precise texture and nature is still an open issue. As for superconductivity, the presence of the spin gap in the normal state points towards d  -wave symmetry and magnetic origin of the attractive interaction. However, there is a finite density of mobile quasi-particles that appears for high Ca contents and increases with pressure, concomitantly with increased two-dimensionality and metallicity. For this reason the superconductivity in the doped ladders of _{Sr14-xCaxCu24O41}${\mathrm{Sr}}_{14-x}{\mathrm{Ca}}_x{\mathrm{Cu}}_{24}{\mathrm{O}}_{41}$ which occurs under high pressure cannot simply be a stabilization of the d-wave superconductivity expected for a pure single ladder system.     

Disordered correlated Kondo-lattice model

We propose a self-consistent approximate solution of the disordered Kondo-lattice model (KLM) to get the interconnected electronic and magnetic properties of ‘local-moment’ systems like diluted ferromagnetic semiconductors. Aiming at (_A1-xMx)$(A_{1-x}{M}_x)$ compounds, where magnetic (M)$(M)$ and non-magnetic (A)$(A)$ atoms distributed randomly over a crystal lattice, we present a theory which treats the subsystems of itinerant charge carriers and localized magnetic moments in a homologous manner. The coupling between the localized moments due to the itinerant electrons (holes) is treated by a modified RKKY-theory which maps the KLM onto an effective Heisenberg model. The exchange integrals turn out to be functionals of the electronic self-energy guaranteeing self-consistency of our theory. The disordered electronic and magnetic moment systems are both treated by CPA-type methods. We discuss in detail the dependencies of the key-terms such as the long-range and oscillating effective exchange integrals, ‘the local-moment’ magnetization, the electron spin polarization, the Curie temperature as well as the electronic and magnonic quasiparticle densities of states on the concentration x of magnetic ions, the carrier concentration n, the exchange coupling J, and the temperature. The shape and the effective range of the exchange integrals turn out to be strongly x-dependent. The disorder causes anomalies in the spin spectrum especially in the low-dilution regime, which are not observed in the mean field approximation.     

Spin dynamics of layered triangular antiferromagnets with uniaxial anisotropy

The spin dynamics of the semiclassical Heisenberg model with uniaxial anisotropy, on the layered triangular lattice with antiferromagnetic coupling for both intralayer nearest neighbor interaction and interlayer interaction is studied both in the ordered phase and in the paramagnetic phase, using the Monte Carlo-molecular dynamics technique. The important quantities calculated are the full dynamic structure function S(q,ω)$S(\mathbf{q},\omega )$, the chiral dynamic structure function _Schi(ω)$S_{\mathrm{chi}}(\omega )$, the static order parameter and some thermodynamic quantities. Our results show the existence of propagating modes corresponding to both S(q,ω)$S(\mathbf{q},\omega )$ and _Schi(ω)$S_{\mathrm{chi}}(\omega )$ in the ordered phase, supporting the recent conjectures. Our results for the static properties show the magnetic ordering in each layer to be of coplanar 3-sublattice type deviating from 120^°${120}^{°}$ structure. In the presence of magnetic trimerization, however, we find the 3-sublattice structure to be weakened along with the tendency towards non-coplanarity of the spins, supporting the experimental conjecture. Our results for the spin dynamics are in qualitative agreement with those from the inelastic neutron scattering experiments performed recently.     

The role of dipolar interaction in nanocomposite permanent magnets

The effects of dipolar interactions on the magnetization behaviors and magnetic properties of the nanocomposite magnets have been studied by micromagnetic simulations. Numerical results show that the dipolar interaction plays an important role during the demagnetization process, especially in the magnets with large soft-phase content _vs$v_{\mathrm{s}}$. For the isotropic nanocomposites, the remanence enhancement can be controlled through adjustments of the grain size D   and _vs$v_{\mathrm{s}}$. However, the appearance of magnetic vortex state leads to a very low remanence in the magnets with large D   and _vs$v_{\mathrm{s}}$. The dependence of coercivity on D   and _vs$v_{\mathrm{s}}$ can be attributed to the exchange-induced magnetization reversal near the grain boundaries and the low nucleation field of soft phase, respectively. For the anisotropic nanocomposites, the reduced remanence _mr$m_{\mathrm{r}}$ is equal to 1.0$1.0$ for the magnets with small D   or with low _vs$v_{\mathrm{s}}$. However, _mr$m_{\mathrm{r}}$ decreases with increasing _vs$v_{\mathrm{s}}$ for the magnet with large D   due to the influence of dipolar interactions. The difference between the calculated coercivity _Hc$H_{\mathrm{c}}$ with and without considering dipolar interaction shows that the dipolar interaction plays a more important role during the magnetization reversal in the soft phase than that in the hard phase. The maximum calculated energy product of the isotropic nanocomposites is only about 40 MGOe due to the conflicting relation between remanence and coercivity, while that of the anisotropic nanocomposites is 112 MGOe. This reminds us that the alignment of hard grain is important to obtain high performance.     

Interface phonons in cylindrical quantum dot heterostructure

The top interface optical (TIO) and side interface optical (SIO) phonon modes of a cylindrical GaAs/ Al_xGa_1−xAs quantum dot are derived within the framework of dielectric continuum approximation. Results reveal that, in the case of taking the “two-mode” behavior of the Al_xGa_1−xAs material into account, there exist eight branches of TIO phonon modes and four branches of SIO phonon modes. The dispersion frequencies of TIO or SIO phonon modes sensitively depend on the Al mole fraction x$x$ in the Al_xGa_1−xAs material. With increasing wavevector q$q$ (κ$\kappa$), the frequency of each TIO (SIO) mode approaches one of the two frequency values of the single Al_xGa_1−xAs heterostructure.     

Exchange bias of mu-metal thin films

The exchange bias of the soft ferromagnet mu-metal, _{Ni77Fe14Cu5Mo4}${\mathrm{Ni}}_{77}{\mathrm{Fe}}_{14}{\mathrm{Cu}}_5{\mathrm{Mo}}_4$, with the metallic antiferromagnet _Fe50Mn50${\mathrm{Fe}}_{50}{\mathrm{Mn}}_{50}$ has been studied as a function of ferromagnet thickness and buffer layer material. Mu-metal exhibits classic exchange bias behavior: the exchange bias (_HEB)$(H_{\mathit{EB}})$ and coercive fields scale inversely with the ferromagnet's thickness, with H_EB varying as the cosine of the in-plane applied field angle. Ta buffers, rather than Cu, allow the mu-metal to retain more of its soft magnetic character while exhibiting exchange bias. The ability to preserve soft ferromagnetic behavior in an exchange biased heterostructure may be useful for low field sensing and other device applications.     

A method of experimentally probing transverse momentum dependent distributions

We calculate the double spin asymmetry A_LL$A_{LL}$ for the π⁰${\pi }^0$ production in semi-inclusive deep inelastic lepton–proton scattering with a spectator model of power-law and a model based on the factorization ansatz. We also calculate the double spin asymmetry for the integration over parts of the kinematic range for the setups of the experiments of COMPASS, HERMES, and JLab. We find that the results are characteristically dependent on the model used. Therefore, we suggest that the measurements of the double spin asymmetry provides a method of experimentally probing the transverse momentum dependent distributions.     

On partition function and Weyl anomaly of conformal higher-spin fields

We study 4-dimensional higher-derivative conformal higher-spin (CHS) fields generalizing Weyl graviton and conformal gravitino. They appear, in particular, as “induced” theories in the AdS/CFT context. We consider their partition function on curved Einstein-space backgrounds like (A)dS or sphere and Ricci-flat spaces. Remarkably, the bosonic (integer spin s) CHS partition function appears to be given by a product of partition functions of the standard 2nd-derivative “partially massless” spin s   fields, generalizing the previously known expression for the 1-loop Weyl graviton (s=2$s=2$) partition function. We compute the corresponding spin s   Weyl anomaly coefficients _as${\mathrm{a}}_s$ and _cs${\mathrm{c}}_s$. Our result for _as${\mathrm{a}}_s$ reproduces the expression found recently in arXiv:1306.5242 by an indirect method implied by AdS/CFT (which relates the partition function of a CHS field on S⁴$S^4$ to a ratio of known partition functions of massless higher-spin field in AdS₅ with alternate boundary conditions). We also obtain similar results for the fermionic CHS fields. In the half-integer s case the CHS partition function on (A)dS background is given by the product of squares of “partially massless” spin s partition functions and one extra factor corresponding to a special massive conformally invariant spin s field. It was noticed in arXiv:1306.5242 that the sum of the bosonic _as${\mathrm{a}}_s$ coefficients over all s is zero when computed using the ζ-function regularization, and we observe that the same property is true also in the fermionic case.     

Theoretical study of diluted Co/Cu alloys

This study employs the self-consistent Green's function method to study the magnetic properties of diluted _CoxCu1-x${\mathrm{Co}}_x{\mathrm{Cu}}_{1-x}$ alloys from a consideration of their spin dynamics characteristics. The numerical results show that in dilute cobalt concentrations (i.e. x?0.4$x?0.4$), the critical temperatures vary linearly with x for different itinerant carrier concentration conditions. Interestingly, the carrier concentration does not affect the degree of dependency of the temperature on the cobalt concentration when the carrier concentration is less than the atomic number concentration of the alloy.