Narrow Results

We present two new algorithms for the estimation of the temperature from a realization of a 2-D Ising model. The methods here introduced are based in the maximization of pseudo likelihood and on the minimum mean squared error (MSE) fit of the conditional probability function. We derive the analytical expressions of these estimators and also we include computational results comparing these new techniques with the traditional method. A very good performance in terms of the average absolute error and the average standard deviation is demonstrated through simulations in a 100 × 100 lattice in the ferromagnetic and antiferromagnetic cases. Summarizing, we have provided two new useful computational tools that allow us to measure the "virtual" temperature of an Ising like system.

We have prepared Ag/BSCCO and Fe/Ag/BSCCO planar junctions to study the effect of Fe exchange field on the tunneling spectra. The junctions were constructed so that the tunneling direction is within the ab-plane, either along the maximum or minimum gap direction. Andreev bound states were observed as zero energy peak in the minimum gap direction. The exchange field caused major splitting of the zero energy peak, which did not occur in Ag/BSCCO junctions. We had detected a few percent (6 to 7%) of s-wave subcomponent at the interface in many of these junctions. This s-wave subcomponent had a T_c of about 20K.

Superconductor-ferromagnetic (FN) metamaterial with effective magnetic shielding and transmittal properties that allow the cloaking and transferring of static magnetic fields has been introduced. Most metamaterials consist of different arrangements of superconducting and ferromagnetic materials whose performance and feasibility mainly depend on the involved materials, their geometrical distribution and the permeability of each. In this paper, combining the method of transformation optics with the design of metamaterials, we experimentally demonstrated a superconductor-FM metamaterial system, composed of two coaxial cylinders of different lengths, to investigate the influence of the length and the properties of superconducting material on the magnetic transferring properties of the magnetic field produced by the permanent magnets. By comparing the transmittal magnetic field of different cases, the optimal structure has been ultimately achieved in terms of calculating the transmitted magnetic field ratios. The insights attained by the present study are aimed to provide useful implications for the design of wireless energy transmission and increasing the efficiency of magnetic transmittal devices.

Onsager reaction field theory is used to investigate the one-dimensional ferromagnetic long-range interacting spin chain with the antiferromagnetic nearest-neighbor interaction (NNI) $\tilde{J}$. The ferromagnetic long-range interactions considered in this paper decay as $J/r^p$ with the distance $r$ between lattice sites. It is found that both the zero temperature and finite-temperature phase diagrams of the system are strongly affected by the interplay between ferromagnetic long-range and antiferromagnetic NNIs. The critical temperature and the uniform susceptibility are obtained as a function of $\alpha =\tilde{J}/J$ and $p$. At finite temperatures and in the region $\alpha <{\alpha }_c(p)$ in which ${\alpha }_c(p)$ is dependent of $p$, the ferromagnetic-paramagnetic phase transition survives for $1<p<2$ and no phase transition exists for $p\ge 2$. At $\alpha ={\alpha }_c(p)$, the ferromagnetic-antiferromagnetic phase transition happens at zero temperature for $p>1$. The ground state of the system keeps ferromagnetic when $\alpha <{\alpha }_c(p)$. But for $\alpha >{\alpha }_c$, the system becomes antiferromagnetic at all temperatures.

In this paper, the electronic structures and magnetic properties of the Cu-doped ZnO monolayer are investigated by means of first-principles methods based on density functional theory. Numerical results show that the Cu dopant can induce the half-metallic ferromagnets in the ZnO monolayer due to the strong p–d coupling. In addition, the semiconductor band gap is also decreased when Zn atom is substituted by Cu atom in the ZnO monolayer. Moreover, the formation energy calculations also indicate that it is energy favorable and relatively easier to incorporate Cu atom into the ZnO monolayer under Zn-rich experimental conditions.

Ternary diamond-like compounds in II–IV–V₂ semiconductor system heavily-doped with transition d-element Mn have been recently prepared. The materials grown in both forms — single crystal layers and polycrystalline bulks — exhibit well defined ferromagnetic hysteresis with a saturation behavior in the magnetization curve up to above room temperature. Curie temperatures are of T_C=310 K to 320 K for (Cd_1-xMn_x)GeP₂ and (Zn_1-xMn_x)GeP₂ compounds. The chemical states in the bulk of ZnGeP₂:Mn and interface of Mn-doped ferromagnetic layer on ZnGeP₂ (001) crystal, have been clarified by electron paramagnetic resonance and in situ photoemission spectroscopy. The as-prepared surface consists of Ge-rich, metallic Mn-compound. In and below the sub-surface region, dilute Mn²⁺ species as precursors of the DMS phase exist. Mn²⁺ ions are paramagnetic active on Zn²⁺ sites in the bulk and show five EPR sets of equidistant peaks. Theoretical band-gap calculation suggests a predominant antiferromagnetic order in stoichiometric (Cd, Mn)GeP₂ but the systems with vacancies as (Cd, V_C, Mn)GeP₂ or (Cd, Ge, Mn)GeP₂ are ferromagnetic and energetically stable. These materials are of great promise for room-temperature spintronics applications.