First principle investigation into structural growth and magnetic properties in GenCr clusters for n=1–13

The ground state structures and their magnetic properties have been investigated for Ge_nCr clusters (1≤n≤13)$(1\le n\le 13)$ using spin polarized density functional theory. The growth behavior of Ge_nCr clusters for n≤13$n\le 13$ shows preference of Cr atom to stabilize at the exohedral position. The binding energy increases with the increase in cluster size, but shows a small decrease w.r.t. pure Ge_n clusters. Interestingly, the magnetic moment in Cr doped Ge_n is found to be either 4_μB$4{\mathrm{\mu }}_{\mathrm{B}}$ or 6_μB$6{\mathrm{\mu }}_{\mathrm{B}}$ and shows no sign of magnetic quenching in any of the ground state structures and isomers investigated up to n  =13. It is found that the magnetic moment is mainly localized at the Cr atom along with small induced magnetic moment on surrounding Ge atoms. The results are consistent with the available theoretical results for n≤5$n\le 5$.     

Magnetic and transport properties of single-crystal Yb3Cu4Ge4

The magnetic and transport properties of single-crystal Yb₃Cu₄Ge₄ with the Gd₃Cu₄Ge₄-type orthorhombic structure are presented. Magnetization along the b-axis at 2 K saturates to 2.8_μB/Yb$2.8{\mu }_{\mathrm{B}}/\mathrm{Yb}$ at 3 kOe, while that along the a- and c-axes at 2 K are gradually increasing to the value of 1.5_μB/Yb$1.5{\mu }_{\mathrm{B}}/\mathrm{Yb}$ and 0.39_μB/Yb$0.39{\mu }_{\mathrm{B}}/\mathrm{Yb}$ at 50 kOe, respectively. The electrical resistivity within the ab-plane shows a metallic behavior in contrast to a broad maximum at around 30 K for that along the c-axis. Each resistivity for the principal axis suddenly decreases below 8 K. The specific heat shows a λ-type$\lambda \mathrm{-}\mathrm{type}$ sharp peak at 7.8 K. The electronic specific heat coefficient is estimated to be 29.4 mJ/mol Yb K² by fitting the magnetic part of the specific heat below 3 K. The magnetic entropy released up to T_C is 68% of that of R ln 2, expected for the doublet ground state. It is revealed that Yb₃Cu₄Ge₄ is categorized to a weak heavy-fermion system showing a ferromagnetic transition at 7.8 K with uniaxial anisotropy along the b-axis.     

The influence of 3d-impurities on magnetic and transport properties of CoSiB metallic glasses

Temperature dependencies of magnetic susceptibility and electric resistivity of Co-based metallic glasses (MGs) of the general composition _Co(72-x)Mex(Si,B₎₂₈${\mathrm{Co}}_{(72-x)}{\mathrm{Me}}_x(\mathrm{Si},\mathrm{B}{)}_{28}$(Me=Fe,Cr,Si:B=18:10)$(\mathrm{Me}=\mathrm{Fe},\mathrm{Cr},\mathrm{Si}:\mathrm{B}=18:10)$ have been studied up to 950 K. The studied MGs were found to be ferromagnets at the room temperature and their Curie point _TC$T_{\mathrm{C}}$ ranges within 260–560 K depending on the dopant contents. At the temperatures higher than _TC$T_{\mathrm{C}}$, a wide paramagnetic region exists. The regularities of magnetic moment variation upon Cr doping evidence a formation of antiferromagnetic clusters, which determine the anomalous behavior of resistivity.     

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.     

Ferromagnetic properties of Fe-substituted ZnO-based magnetic semiconductor

The diluted magnetic semiconductor Zn_1−x⁵⁷Fe_xO (x=0.01, 0.02, 0.03) compounds were prepared by the solid-state reaction method. The crystal structure of _Zn0.97⁵⁷_Fe0.03O${\mathrm{Zn}}_{0.97}{}^{57}{\mathrm{Fe}}_{0.03}\mathrm{O}$ at room temperature is determined to be a hexagonal structure of P6₃mc with lattice constants a₀=3.252 Å and c₀=5.205 Å by Rietveld refinement. The Bragg factors R_B and R_F were determined as 3.23% and 2.81%. From the inverse susceptibility versus T curve, the paramagnetic Curie temperature is found to be 2.7 K and effective moment is found to be 4.01 μ_B, thereby suggesting that the exchange interactions between Fe ions are ferromagnetic. Mössbauer spectra of _Zn0.97⁵⁷_Fe0.03O${\mathrm{Zn}}_{0.97}{}^{57}{\mathrm{Fe}}_{0.03}\mathrm{O}$ have been taken at various temperatures ranging from 4.2 to 295 K. Mössbauer spectrum for _Zn0.97⁵⁷_Fe0.03O${\mathrm{Zn}}_{0.97}{}^{57}{\mathrm{Fe}}_{0.03}\mathrm{O}$ at 4.2 K has shown ferromagnetic phase (sextet), and the spectra were fitted based on a random distribution model of Fe ions.     

Decaying hidden gaugino as a source of PAMELA/ATIC anomalies

We study a scenario that a U(1)$\mathrm{U}(1)$ hidden gaugino constitutes the dark matter in the Universe and decays into a lepton and slepton pair through a mixing with a U_(1)B–_L$\mathrm{U}{(1)}_{\mathrm{B}\text{–}\mathrm{L}}$ gaugino. We find that the dark-matter decay can account for the recent PAMELA and ATIC anomalies in the cosmic-ray positrons and electrons without an overproduction of antiprotons.     

Determination of the Landau–Lifshitz damping parameter by means of complex susceptibility measurements

A new experimental method for the determination of the Landau–Lifshitz damping parameter, α$\alpha$, based on measurements of the frequency and field dependence of the complex magnetic susceptibility, χ(ω,H)=χ^′(ω,H)-iχ^″(ω,H)$\chi (\omega ,H)={\chi }^{\prime }(\omega ,H)-\mathrm{i}{\chi }^{″}(\omega ,H)$, is proposed. The method centres on evaluating the ratio of f_max/f_res, where f_res is the resonance frequency and f_max is the maximum absorption frequency at resonance, of the sample susceptibility spectra, measured in strong polarizing fields. We have investigated three magnetic fluid samples, namely sample 1, sample 2 and sample 3. Sample 1 consisted of particles of Mn_0.6Fe_0.4Fe₂O₄ dispersed in kerosene, sample 2 consisted of magnetite particles dispersed in Isopar M and sample 3 was composed of particles of Mn_0.66Zn_0.34Fe₂O₄ dispersed in Isopar M  . The results obtained for the mean damping parameter of particles within the magnetic fluid samples are as follows: 〈α(_{Mn0.6Fe0.4Fe2O4})〉=0.057$〈\alpha ({\mathrm{Mn}}_{0.6}{\mathrm{Fe}}_{0.4}{\mathrm{Fe}}_2{\mathrm{O}}_4)〉=0.057$ with the corresponding standard deviation SD=0.0104$\mathrm{SD}=0.0104$; 〈α(_Fe3O4)〉=0.1105$〈\alpha ({\mathrm{Fe}}_3{\mathrm{O}}_4)〉=0.1105$ with the corresponding standard deviation, SD=0.034$\mathrm{SD}=0.034$ and 〈α(_{Mn0.66Zn0.34Fe2O4})〉=0.096$〈\alpha ({\mathrm{Mn}}_{0.66}{\mathrm{Zn}}_{0.34}{\mathrm{Fe}}_2{\mathrm{O}}_4)〉=0.096$ with the corresponding standard deviation, SD=0.037$\mathrm{SD}=0.037$.     

Surface magnetic phase transitions in films

Using a simple Landau model, we discuss the different possibilities of generating magnetic effects at a second-order transition for films. Varying the sample size d$d$ and/or surface coupling γ$\gamma$ one can decrease or increase substantially the surface critical temperature _Ts$T_{\mathrm{s}}$ and the saturation magnetization _Ms$M_{\mathrm{s}}$. In the case of γ>0$\gamma >0$, _Ms$M_{\mathrm{s}}$ and _Ts$T_{\mathrm{s}}$ decrease from the bulk values as the film thickness is reduced. These theoretical results are in nice agreement with the experimental data on superconducting _MgB2${\mathrm{MgB}}_2$ thin films. By contrast, for γ<0$\gamma <0$, an enhancement of both quantities is expected. This extraordinary transition has rarely been observed experimentally and, usually, the situation is far from being clear. We analyze a new experiment on _NiFe2O4${\mathrm{NiFe}}_2{\mathrm{O}}_4$ ultra-thin films, where a very strong enhancement of the saturation magnetization is observed.     

Shot noise in HTc superconductor quantum point contact system

We study the electrical transport properties of a quantum point contact between a lead and a high Tc superconductor. For this, we use the Hamiltonian approach and non-equilibrium Green functions of the system. The electrical current and the shot noise are calculated with this formalism. We consider d_x²−y²${\mathrm{d}}_{x^2-y^2}$, d_xy${\mathrm{d}}_{\mathit{xy}}$, d_x²−y²+is${\mathrm{d}}_{x^2-y^2}+\mathrm{is}$ and d_xy+is${\mathrm{d}}_{\mathit{xy}}+\mathrm{is}$ symmetries for the pair potential. Also we explore the s₊₋${\mathrm{s}}_{+-}$ and s₊₊${\mathrm{s}}_{++}$ symmetries describing the behavior of the ferropnictides superconductors. We found that for d_xy${\mathrm{d}}_{\mathit{xy}}$ symmetry there is not a zero bias conductance peak and for d+is$\mathrm{d}+\mathrm{is}$ symmetries there is a displacement of the transport properties. From shot noise and current, the Fano factor is calculated and we found that it takes values of effective charge between e and 2e  , this is explained by the diffraction of quasiparticles in the contact. For the s₊₋${\mathrm{s}}_{+-}$ and s₊₊${\mathrm{s}}_{++}$ symmetries the results show that the electrical current and the shot noise depend on the mixing coefficient, furthermore, the effective electric charge can take values between 0 and 2e, in contrast with the results obtained for s wave superconductors.     

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.     

On the Riemannian geometry of Seiberg–Witten moduli spaces

We construct a natural L²$L^2$-metric on the perturbed Seiberg–Witten moduli spaces _Mμ+${\mathfrak{M}}_{{\mu }^{+}}$ of a compact 4-manifold M$M$, and we study the resulting Riemannian geometry of _Mμ+${\mathfrak{M}}_{{\mu }^{+}}$. We derive a formula which expresses the sectional curvature of _Mμ+${\mathfrak{M}}_{{\mu }^{+}}$ in terms of the Green operators of the deformation complex of the Seiberg–Witten equations. In case M$M$ is simply connected, we construct a Riemannian metric on the Seiberg–Witten principal U(1)$U\left(1\right)$ bundle P→_Mμ+$\mathfrak{P}\to {\mathfrak{M}}_{{\mu }^{+}}$ such that the bundle projection becomes a Riemannian submersion. On a Kähler surface M$M$, the L²$L^2$-metric on _Mμ+${\mathfrak{M}}_{{\mu }^{+}}$ coincides with the natural Kähler metric on moduli spaces of vortices.     

First-principles study on the metallic antiferromagnet Co[PhPO3]·H2O

The electronic structure and the magnetic properties of transition metal phosphonate Co(PhPO₃)·H₂O have been studied by first-principles within the density-functional theory (DFT) and the full potential linearized augmented plane wave (FP-LAPW) method. The total energy, the total magnetic moment, the atomic spin magnetic moments and the density of states(DOS) of Co(PhPO₃)·H₂O were all calculated. The calculations reveal that the title compound is a metallic antiferromagnet and has a metallic ferromagnetic metastable state, which are in good agreement with the experiment. The spin magnetic moment of Co(PhPO₃)·H₂O is about 4.93 _μB${\mu }_{\mathrm{B}}$ per molecule, and it is mainly assembled at the cobalt atom, at the same time, with a little contribution from the P, O1, O2, O3.