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This paper discusses a level set-based topology optimization method for the design of a ferromagnetic waveguide. The optimization problem is formulated to maximize the power of transmitted waves at prescribed frequencies. A level set-based topology optimization method incorporating a fictitious interface energy is used to find optimized configurations of ferrite materials inside the waveguide. The results of the numerical examples for two different target frequencies show that the presented method successfully finds optimized configurations that maximize transmission power of waveguides for both forward and backward propagation. [ABSTRACT FROM PUBLISHER]

Multiferroic heterostructure (Ba0.5Sr0.5)TiO3(BST)/BiFeO3(BFO) have been deposited by pulsed laser deposition method. X-ray diffraction shows that the BFO and BST were epitaxial grown on La0.7Sr0.3MnO3-buffered (100) SrTiO3 substrate. Interestingly, the BST/BFO heterostructure exhibits improved ferroelectric and ferromagnetic behaviors with remnant polarization (2\Pr)\sim 34.8\ \muC/cm^2 and saturation magnetization (Ms)\sim 4.65\ emu/cm^3. Compared with the single BFO film, the BST/BFO heterostructure showed higher dielectric constant and lower dielectric loss. Furthermore, the leakage behaviors of the BST/BFO heterostructure were consistent with SCLC behavior at low electric-field region and PF emission at high electric-field region. Our result indicates the BST/BFO multiferroic heterostructure may be a promising material for the high-density memory application. [ABSTRACT FROM PUBLISHER]

We report the structure, magnetic and dielectric properties of CuO nanoparticles synthesized by co-precipitation method. The magnetic measurements reveal the presence of a ferromagnetic (FM) component at room temperature with coercivity of 200 Oe and saturation magnetization of 0.004 emu/g. The observed FM may originate from different valence states of the copper ions due to the oxygen vacancies at the surface/or interface of the particles. In addition, these nanoparticles also exhibit a high dielectric permittivity (\varepsilon^\prime\sim 10^4) with weak temperature dependence in a wide range of temperature. Such a room temperature FM and giant dielectric permittivity without the presence of any transition metal could be a very good option for a class of spintronics. [ABSTRACT FROM AUTHOR]

This paper develops a physically-based analytical theory that can be used to model recoil loops, as well as major loops and first- and second-order return curves, in hard ferromagnetic materials that display return-point memory. Atomic-scale quantum-mechanical considerations lead to basic S-shaped magnetization curves that account for hysteretic effects in major and minor loops, as well as their reversibility and irreversibility. These loops exhibit perfect closure only in the presence of the return-point-memory effect. Field (energy) contributions from this hysteretic scenario are summed with contributions due to the classical-physics domain-scale anhysteretic scenario and to the macroscopic demagnetizing field, to obtain a summed scenario that can model isotropic and certain anisotropic materials. Analytical expressions are obtained for all reversal curves up to second order, under the return-point-memory constraint, so that closed recoil loops can be modeled. The theory is validated by comparison with measured data for five different materials. [ABSTRACT FROM AUTHOR]

This paper describes the synthesis and magnetic properties of multifunctional Fe3O4-AuPt core-shell nanoparticles. The Fe3O4-Au Pt core-shell nanoparticles were synthesized by a one-pot polyol process in two consecutive steps from Fe, Au, and Pt precursors. The structural characterization and property analysis proves the formation of the core-shell nanostructure fusing the multifunctionality in a single entity. The TEM observation shows that the Fe3O4-AuPt core-shell nanoparticles are highly crystalline and uniform in size distribution, with an averaged particle size of ~12.5 nm in diameter, whereas the X-ray diffraction patterns provide further substantiation. The surface plasmon resonance arising from the AuPt nano-shell was revealed by UV-vis spectroscopy, while the magnetic measurements by YSM and PPMS demonstrate the well-defined superparamagnetic and/or soft-ferromagnetic behavior of the Fe3O4-AuPt core-shell nanoparticles. [ABSTRACT FROM AUTHOR]

Based on quantum mechanics and classical physics, a general analytical theory of ferromagnetic first order return curves is developed. No empirical assumptions or approximations are required. [ABSTRACT FROM PUBLISHER]

We present a theoretical study of spin ploarized transport in a single-electron tunneling transistor with ferromagnetic source and drain electrodes. The sequential tunneling and cotunneling currents are analyzed as a function of the intrinsic spin polarization of the electrodes, and spin flip effects within the central island electrode, for the case of collinear magnetization configuration. It was found that an antiparallel alignment of the electrode magnetization leads to a suppression of both the sequential tunneling and cotunneling currents, with the degree of suppression being greater for the higher order cotunneling current. For the sequential case, the suppression can be reduced by introducing finite spin flip within the island, but this has virtually no effect on the cotunneling current. [ABSTRACT FROM AUTHOR]

A physically based hysteresis theory incorporating a domain size that depends on the Weiss effective field explains the observed ranges of reversible and irreversible magnetization in the initial-magnetization curve and exterior loop of ferromagnetic materials. The theory applies to materials exhibiting both normal and wasp-waisted exterior loops and agrees well with measured data. It also provides close linkages between magnetization at the quantum scale, domain properties at the mesoscopic scale, and measurements at the macroscopic scale. [ABSTRACT FROM AUTHOR]

Ti1-xFexO2 and Ti1-2xFexNbxO2 (x = 0.0,0.01) powders were synthesized by the sol-gel method. X-ray diffraction patterns showed a pure anatase single phase and no different peaks other than anatase titanium dioxide were observed. Mössbauer spectra of all samples showed that the magnetically ordered and paramagnetic phases coexisted in all temperature ranges (4.2-295 K), where Fe is not metallic but in the +3 state substituting for Ti. Although the Fe/Nb co-doped samples showed more magnetically ordered phase than Fe-single-doped samples with the same amount of Fe ions in 295 K spectra, the smaller magnetic moments were observed in Fe/Nb co-doped samples. This result suggests that the Nb co-doping decreases the ferromagnetic contribution of Fe ions in TiO2 and increases the antiferromagnetic contribution. [ABSTRACT FROM AUTHOR]

We report the synthesis of zinc-blende CrTe (zb-CrTe) as highly oriented crystalline grains in films of 100-nm thickness. The structural properties of the film were characterized using high-resolution transmission electron microscopy (HRTEM) and selective-area electron diffraction (SAED). Temperature-dependent magnetization measurements show that the Curie temperature of the film is ∼327 K. Angular M-H measurements indicate that the CrTe films have an in-plane easy axis of magnetization along the [01¯1] direction of GaAs. [ABSTRACT FROM AUTHOR]

In this paper, we propose an alternative method to improve magnetoresistance by inserting a thin ferromagnetic (FM) layer into the nonmagnetic (NM) spacer of a basic spin-valve (SV) trilayer (FM1-NM-FM1), thus creating a penta-layer SV structure (FM1-NM- FM2-NM-FM1). We investigated the effect of increasing the resistivity (ρF2) of the FM2 on overall magnetoresistance (MR). We performed both analytical and numerical studies on the MR of the current perpendicular-to-plane (CPP) structure using the phenomenological spin drift-diffusion models. For finite ρF2, the MR profile is dependent on the intrinsic conductance polarization (αF2) of FM2. We found that inserting FM2 enhances MR when αF2 exceeds a critical value of α2C. It is found that MR can be doubled by inserting a FM layer with high αF2, such as the half-metallic Cr2O. We have numerically calculated MRmax and the corresponding ρF20 values for different αF2 values. Finally, we studied the effect of spin relaxation on the MR of the CPP SV. [ABSTRACT FROM AUTHOR]

Ti1-xFexO2 and Ti1-2xFexNbxO2 (x = 0.0,0.01) powders were synthesized by the sol-gel method. X-ray diffraction patterns showed a pure anatase single phase and no different peaks other than anatase titanium dioxide were observed. Mössbauer spectra of all samples showed that the magnetically ordered and paramagnetic phases coexisted in all temperature ranges (4.2-295 K), where Fe is not metallic but in the +3 state substituting for Ti. Although the Fe/Nb co-doped samples showed more magnetically ordered phase than Fe-single-doped samples with the same amount of Fe ions in 295 K spectra, the smaller magnetic moments were observed in Fe/Nb co-doped samples. This result suggests that the Nb co-doping decreases the ferromagnetic contribution of Fe ions in TiO2 and increases the antiferromagnetic contribution. [ABSTRACT FROM AUTHOR]

Zn1-xFexO (x = 0.00, 0.01, 0.03, 0.05, 0.07, and 0.10) compounds were fabricated by the sol-gel method. The crystal structure and magnetic properties were investigated as a function of doped Fe concentration. Specifically, we have used hydrogen treatment for the control of phase separation. The X-ray diffraction patterns show that the wurzite structure of ZnO does not change for the doping range below x = 0.07. Furthermore, we could not find any Fe cluster or phase separation in the X-ray diffraction patterns. The Fe-doped ZnO indicate ferromagnetic behaviors with the Curie temperature higher than room temperature. Then, the magnetic moment per Fe atom increased with increasing Fe concentration. [ABSTRACT FROM AUTHOR]