The effective medium approximation for annealed magnetoelectric polycrystals
ABSTRACT Magnetoelectric polycrystals usually possess antiferromagnetic domains with oppositive magnetoelectric coefficients, and have to be annealed under the appropriate electric and magnetic fields to make the polycrystals macroscopically magnetoelectric. In this paper, we developed an effective medium approximation to calculate the macroscopic coefficients of magnetoelectric polycrystals annealed through Néel’s temperature, and studied the effects of temperature as well as shape and orientation distribution of grains on the macroscopic magnetoelectric coefficients of polycrystalline Cr 2 O 3 . It is observed that the effective magnetoelectric coefficient of polycrystal is higher than single-crystalline a11 but lower than single-crystalline a33 , and that calculated from the effective medium approximation is higher than simple volume averaging and agrees with experimental data better. It is also noted that polycrystals with randomly oriented grains are optimal for a11* , while those with fiber texture are optimal for a33* . In addition, the lamellar grain is optimal for the effective magnetoelectric coupling, with the magnetoelectric coefficient about 20% higher than those with spherical grains.
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ABSTRACT: The regularity of the four time-harmonic vector fields composing any strong solution of the system obtained from Maxwell's curl equations and the constitutive relations in the interior of an inhomogeneous bianisotropic material is investigated. The results are given as interior Sobolev or Hölder regularity. Possible local C ∞ regularity or local analyticity of the four vector fields are discussed, too. Each of these regularity results is obtained under specific conditions on the impressed current densities and on the constitutive parameters of the bianisotropic material considered, but it is shown that such conditions do not significantly limit the coverage of our analysis in terms of applications. Keywords: Time-harmonic Maxwell's equations; interior Sobolev regularity of electromagnetic fields; interior Hölder regularity of electromagnetic fields; analyticity of electromagnetic fields; anisotropic media and metamaterials; bianisotropic media and metamaterials.IMA Journal of Applied Mathematics 01/2012; 79(1). DOI:10.1093/imamat/hxs039
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ABSTRACT: A model is proposed for a device combining a multiferroic tunnel junction with a magnetoelectric (ME) film in which the magnetic configuration is controlled by the electric field. Calculations embodying the Green's function approach show that the magnetic polarization can be switched on and off by an electric field in the ME film due to the effect of elastic coupling interaction. Using a model including the spin-filter effect and screening of polarization charges, we have produced eight logic states of tunnelling resistance in the tunnel junction and have obtained corresponding laws that control them. The results provide some insights into the realization of an eight-logic memory cell.Journal of Physics D Applied Physics 03/2009; 42(7):072004. DOI:10.1088/0022-3727/42/7/072004
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ABSTRACT: Magnetoelectric annealing is necessary to remove antiferromagnetic domains and induce macroscopic magnetoelectric effect in polycrystalline magnetoelectric materials, and in this paper, we study the effective magnetoelectric properties of perpendicularly annealed polycrystalline Cr <sub>2</sub> O <sub>3</sub> using effective medium approximation. The effect of temperatures, grain aspect ratios, and two different types of orientation distribution function have been analyzed, and unusual material symmetry is observed when the orientation distribution function only depends on Euler angle ψ . Optimal grain aspect ratio and texture coefficient are also identified. The approach can be applied to analyze the microstructural field distribution and macroscopic properties of a wide range of magnetoelectric polycrystals.Journal of Applied Physics 05/2009; 105(7-105):073917 - 073917-5. DOI:10.1063/1.3106000