Structural characterization and magnetization of Mg0.7Zn0.3SmxFe2−xO4 ferrites

Mg_0.7Zn_0.3Sm_xFe_2−xO₄ ferrites were prepared by the solid-state reaction method and were characterized by X-ray diffraction and magnetization measurements. A single spinel phase was obtained in the range 0.00?x?0.03$0.00?x?0.03$. The lattice parameter was found to increase at x=0.01$x=0.01$ and then decreases up to x=0.03$x=0.03$, which may indicate a distortion in the spinel lattice. The saturation magnetization was found to decrease with the increase in x up to 0.04, due to the replacement of the Fe³⁺ ions by the Sm³⁺ ions.     

Magnetic entropy-change in La0.67−xBixCa0.33MnO3 compound

Bi doped lanthanum manganites with the chemical composition of La_0.67−xBi_xCa_0.33MnO₃ (x=0$x=0$, 0.05, 0.1, 0.2) were prepared by the standard solid-state process. The Curie temperatures were measured to be 267 K for x=0$x=0$, 248 K for x=0.05$x=0.05$, 244 K for x=0.1$x=0.1$ and 229 K for x=0.2$x=0.2$ samples. It was found that the maximum value of the magnetic entropy change ∣ΔS_m∣ has reached the highest value of 6.08 J/kg K at 3 T for the composition with x=0.05$x=0.05$. Nearly the same maximum entropy change was observed for the x=0$x=0$ sample. A large decrease in the magnitude of the entropy change was observed for the x=0.2$x=0.2$ sample.     

Effect of carbon content on structure and magnetic properties for (Fe,Ni)1−xCx by mechanical alloying

FCC (Fe₅₅Ni₄₅)_1−xC_x   supersaturated solid solution was prepared in a wide concentration range (0?x?0.9)$(0?x?0.9)$ by mechanical alloying of nanocrystalline Fe₅₅Ni₄₅ with graphite. The lattice constant of Fe₅₅Ni₄₅ increases linearly with increasing carbon content up to x=0.25$x=0.25$. At the same time, it is found that the magnetic moment per metal atom (Fe, Ni) decreases linearly with increasing carbon content for 0?x?0.25$0?x?0.25$ with a slope of 1.2 μ_B/at. For high carbon content, x?0.5$x?0.5$, it is observed that the decrease of lattice constant and increase of moment per metal atom (Fe, Ni) with increasing C content, indicates that the dissolution of carbon is hindered by the high-volume fraction of graphite in the initial powder mixture. The complete amorphization of x=0.5$x=0.5$ does not occur after the extended ball milling. The alloying effect of carbon on the magnetization is compared with other metalloid B, P, and Si in Fe- and Ni-based binary system.     

Effect of La doping on magnetotransport and magnetic properties of double perovskite Sr2FeMoO6 system

We have investigated the magnetotransport and magnetic properties on polycrystalline samples of Sr_2−xLa_xFeMoO₆ (x=0$x=0$, 0.2, 0.4, 0.6, 0.8 and 1.0). The magnitude of intergrain tunneling magnetoresistance with low magnetic field of 0.88 T for x=0.2$x=0.2$ and 0.4$0.4$ samples are as large as 5% and 7% at room temperature and 13% and 10% at 10 K, respectively. The increase of coercivity (_Hc$H_{\mathrm{c}}$), ratio of remanent magnetization with respect to saturation magnetization (_Mr/_Ms$M_{\mathrm{r}}/M_{\mathrm{s}}$), high saturation fields, and reduction of the saturation magnetization indicate that random disorder of spin orientation is mainly responsible for enhancement of the low-field magnetoresistance for samples with x?0.4$x?0.4$. Whereas rapid drop of _Hc$H_{\mathrm{c}}$, _Mr/_Ms$M_{\mathrm{r}}/M_{\mathrm{s}}$, _Mr$M_{\mathrm{r}}$, and saturation fields for samples with x>0.4$x>0.4$ signifies the growth of antiphase boundary, which gives rise to lower values of low-field MR.     

Magnetocaloric effect of Gd5SixSn4−x Alloys

The crystal structure and magnetocaloric effect of Gd₅Si_xSn_4−x   (with x=2.4$x=2.4$, 2.6 and 2.8) alloys were studied by means of X-ray power diffraction (XRD) and magnetic measurements. From the XRD results, these alloys adopt a Gd₅Si₄-type structure for x=2.8$x=2.8$, Gd₅Si₄-type and Gd₅Si₂Ge₂-type mixed structures for x=2.4$x=2.4$ and 2.6, while some minor phases can also be found. The Curie temperatures of the Gd₅Si_xSn_4−x increases gradually when x increases from 276 K for x=2.4$x=2.4$, to 301.5 K for x=2.8$x=2.8$. Magnetic entropy changes of these alloys at a magnetic field change of 0–1.8 T are 1.88, 2.26 and 1.69 J/kg K for x=2.4$x=2.4$, 2.6 and 2.8, respectively. The temperature-dependent XRD analysis shows that there is no crystallographic transition for these alloys, which can explain their low magnetic entropy changes.     

Angular dependence of tunneling magnetoresistance in La0.7Sr0.3MnO3 step-edge junctions

La_0.7Sr_0.3MnO₃ (LSMO) tunneling magnetoresistance (TMR) junctions have been fabricated on step-edge (0 0 1) SrTiO₃ substrates with a high step-edge angle. In the measurement of magnetoresistance (MR) ratio versus external magnetic field H, butterfly-like MR curves are clearly observed. The MR(H  ) curves vary with θ$\theta$, the angle between the applied magnetic field and the current direction in the substrate plane, showing anisotropic MR properties. A much broader MR(H) response is observed for the configuration of H perpendicular to the substrate plane. Additionally, the maxima-MR field H_p almost coincides with the coercive field H_c for θ<60°$\theta <60°$ but obeys a different form from _Hc(θ)$H_{\mathrm{c}}(\theta )$. The high-field junction resistance shows an intrinsic sin²θ${\sin }^2\theta$ angular dependence, while the low-field resistance shows an extrinsic cos(4θ)$\cos (4\theta )$ angular dependence. The distinctive features are mainly due to the induced magnetization anisotropy in the artificial steps of grain boundaries.     

Structure and magnetic phase diagram of mixed rare-earth Nd1−xTbxFe10.5Mo1.5 compounds

The structural and magnetic properties of Nd_1−xTb_xFe_10.5Mo_1.5 (x=0$x=0$, 0.2, 0.4, 0.6, 0.8, 1.0) compounds have been investigated by means of X-ray diffraction and magnetic measurements. All the investigated compounds crystallize in the tetragonal ThMn₁₂-type structure with I4/mmm space group. The lattice parameters a, c and the unit-cell volume V decrease with increasing x. The Curie temperatures T_C are almost independent x. There exists a unique spin-reorientation transition for the end compositions of Nd_1−xTb_xFe_10.5Mo_1.5 compounds with x=0$x=0$ and x=1$x=1$, while two spin-reorientation transitions are observed for x=0.2–0.8$x=0.2–0.8$. The room-temperature magnetocrystalline anisotropy of Nd_1−xTb_xFe_10.5Mo_1.5 compounds changes from uniaxial to planar with increasing x content. Based on magnetic measurements, a magnetic phase diagram of Nd_1−xTb_xFe_10.5Mo_1.5 compounds is constructed. By minimizing the magnetocrystalline anisotropy energy, a theoretical magnetic phase diagram for the Nd_1−xTb_xFe_10.5Mo_1.5 system is derived, showing a reasonable agreement with the observations.     

Effects of Ag addition on electrical transport and magnetic properties of La0.67Ba0.33Mn0.88Cr0.12O3

We have prepared a series of polycrystalline manganites with the nominal compositions, La_0.67Ba_0.33Mn_0.88Cr_0.12O₃/Ag_x (LBMCO/Ag_x) (x   is the mole fraction) with x=0$x=0$, 0.05, 0.1, 0.15, 0.2, 0.23, 0.27, 0.3, 0.35. The X-ray diffraction patterns show that the samples with x>0.05$x>0.05$ are two-phase composites. The Ag addition in LBMCO improves the properties of grain surfaces/boundaries and reduces the resistivity of the composites. For x=0.30$x=0.30$ sample, a minimum resistivity is obtained and a maximum room temperature magnetoresistance up to −54.5% was observed at 288 K, 1 T field. The room temperature T_C and the reduced resistivity are responsible for the enhancement of room temperature MR.     

Magnetic and optical properties of spinel FexCo3−xO4 thin films

Magnetic and optical properties of Fe_xCo_3−xO₄ thin films grown by sol–gel method have been investigated as the Fe composition (x  ) increases from 0 to 2. X-ray diffraction measurements revealed that the normal- and inverse-spinel phases coexist for 0.76?x?0.93$0.76?x?0.93$. The normal-spinel phase is dominant below x=0.76$x=0.76$ while the inverse-spinel phase above x=0.93$x=0.93$. The lattice constant of the inverse-spinel phase is found to be larger than that of the normal-spinel phase. For both phases the lattice constant increases with increasing x. The Fe_xCo_3−xO₄ films containing the inverse-spinel phase exhibit net magnetization that increases with increasing x  . Conversion electron Mössbauer spectrum measured on the x=0.93$x=0.93$ sample showed that Fe²⁺ ions prefer the octahedral sites, indicating the formation of the inverse-spinel phase. Analysis on the measured optical absorption spectra for the samples by spectroscopic ellipsometry indicates a dominance of the normal-spinel phase for low x in which Fe³⁺ ions mostly occupy the octahedral sites. Observation of a crystal-field transition at 1.6 eV originating from tetrahedral Fe³⁺ ion confirms the existence of the inverse-spinel phase for high x.     

Magnetic properties and magnetocaloric effect in Dy(Co1−xFex)2 alloys

Polycrystalline samples of Laves-phase alloys Dy(Co_1−xFe_x)₂(x=0$x=0$, 0.02,0.04,0.06,0.08) have been prepared by arc-melting method. No first order phase transition was observed for samples with x≠0$x\ne 0$. With the increase of Fe content, the Curie temperature increases greatly, while the calculated magnetic entropy change, ΔS_M, shows an obvious decrease with a broader peak. The origin of the magnetocaloric effect in Dy(Co_1−xFe_x)₂ alloys has been discussed.     

The extended Higgs system in R-symmetric supersymmetry theories

The Higgs sector is extended in R  -symmetric supersymmetry theories by two iso-doublets R_d,u$R_{d,u}$ which complement the standard iso-doublets H_d,u$H_{d,u}$. We have analyzed masses and interactions of these novel states and describe their [non-standard] decay modes and their production channels at the LHC and e⁺e⁻$e^{+}{e}^{-}$ colliders.     

Terahertz spectroscopy of multiferroic EuFe3(BO3)4

The terahertz spectra of a rare-earth iron borate with the huntite structure are obtained for the first time. We study the low-temperature (4.0–90 K) α-polarized transmittance spectra of the EuFe₃(BO₃)₄ single crystal in the region 0.9–6.0 THz. Pronounced shifts of phonon frequencies and appearance of new phonon modes at the temperature _TS=58 K$T_S=58\text{K}$ of the R32→P₃₁21$R32\to P{3}_{1}21$ structural phase transition are observed. Additional shifts of phonon frequencies occur at the temperature _TN=34 K$T_N=34\text{K}$ of the magnetic ordering of the Fe subsystem, thus evidencing the spin–phonon coupling in this multiferroic material.     

Effect of Co ions on the microstructure and magnetic properties of nanocrystalline CoxFe3−xO4 films

Co_xFe_3−xO₄ nanocrystalline films (x=0.2-0.8$x=0.2-0.8$) on SiO₂ substrates were prepared by a sol–gel method. The microstructural and magnetic properties of samples were measured by an X-ray diffractometer (XRD) and a vibrating sample magnetometer (VSM), respectively. Atomic force microscopy (AFM) was used to investigate the surface image of the sample. The measurement results of XRD at room temperature show that the pure spinel structure of the film could be obtained at x=0.8$x=0.8$. The magnetic measurements reveal the magnetic properties of the samples depend strongly on Co²⁺ ions content, and the optimal parameters of the saturation magnetization and coercivity in Co_xFe_3−xO₄films are obtained at x=0.8$x=0.8$. Here the coercivity reaches 1.954 kOe. The average grain sizes of the film are less than 30 nm obtained from the microscopy images. The situ measurement at high temperatures of range from 293 to 773 K shows that the microstructures of Co_0.8Fe_2.2O₄ film have good thermal stabilization.     

Dworkin’s argument revisited: Point processes,dynamics, diffraction,and correlations

The setting is an ergodic dynamical system (X,μ)$(X,\mu )$ whose points are themselves uniformly discrete point sets Λ$\Lambda$ in some space R^d${\mathbb{R}}^d$ and whose group action is that of translation of these point sets by the vectors of R^d${\mathbb{R}}^d$. Steven Dworkin’s argument relates the diffraction of the typical point sets comprising X$X$ to the dynamical spectrum of X$X$. In this paper we look more deeply at this relationship, particularly in the context of point processes.     

Metal-like to insulator transition in Lu3Fe5O12

Polycrystalline Lu₃Fe₅O₁₂, prepared using the solid state reaction method, has Fe in the mixed valence state as inferred from the X-ray photoelectron spectroscopy. A spectral change in the impedance plot at 343 K is attributed to metal-like to insulator transition (MIT), which is analyzed in terms of localized and delocalized _eg$e_g$ electrons. The change in the slope at 343 K in the DC conductivity plot also proves the MIT. The dependence of Z^′${\mathrm{Z}}^{\prime }$ on temperature and Z^″${\mathrm{Z}}^{″}$ on frequency clearly substantiates the presence of localized electrons up to 343 K and delocalized electrons above 343 K.     

The H2+ molecular ion: Low-lying states

Matching for a wavefunction the WKB expansion at large distances and Taylor expansion at small distances leads to a compact, few-parametric uniform approximation found in Turbiner and Olivares-Pilon (2011). The ten low-lying eigenstates of H₂⁺ of the quantum numbers (n,m,Λ,±)$(n,m,\Lambda ,\pm )$  with n=m=0$n=m=0$ at Λ=0,1,2$\Lambda =0,1,2$, with n=1$n=1$, m=0$m=0$ and n=0$n=0$, m=1$m=1$ at Λ=0$\Lambda =0$ of both parities are explored for all interproton distances R$R$. For all these states this approximation provides the relative accuracy ?10⁻⁵$?10^{-5}$ (not less than 5 s.d.) locally, for any real coordinate x$x$ in eigenfunctions, when for total energy E(R)$E\left(R\right)$ it gives 10-11 s.d. for R∈[0,50]$R\in [0,50]$  a.u. Corrections to the approximation are evaluated in the specially-designed, convergent perturbation theory. Separation constants are found with not less than 8 s.d. The oscillator strength for the electric dipole transitions E1$E1$ is calculated with not less than 6 s.d. A dramatic dip in the E1$E1$ oscillator strength f_{1sσg−3pσu}$f_{1s{\sigma }_g-3p{\sigma }_u}$ at R∼R_eq$R\sim R_{eq}$ is observed. The magnetic dipole and electric quadrupole transitions are calculated for the first time with not less than 6 s.d. in oscillator strength. For two lowest states (0,0,0,±)$(0,0,0,\pm )$ (or, equivalently, 1sσ_g$1s{\sigma }_g$ and 2pσ_u$2p{\sigma }_u$ states) the potential curves are checked and confirmed in the Lagrange mesh method within 12 s.d. Based on them the Energy Gap between 1sσ_g$1s{\sigma }_g$ and 2pσ_u$2p{\sigma }_u$ potential curves is approximated with modified Pade Re^−R[Pade(8/7)](R)$R{e}^{-R}\left[Pade(8/7)\right]\left(R\right)$ with not less than 4-5 figures at R∈[0,40]$R\in [0,40]$ a.u. Sum of potential curves E_1sσg+E_2pσu$E_{1s{\sigma }_g}+E_{2p{\sigma }_u}$ is approximated by Pade 1/R[Pade(5/8)](R)$1/R\left[Pade(5/8)\right]\left(R\right)$ in R∈[0,40]$R\in [0,40]$ a.u. with not less than 3-4 figures.