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: 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; · 2.21 Impact Factor