Magnetoelectric Coupling and Overall Properties of a Class of Multiferroic Composites

Abstract

In this chapter we present a widely useful composite model for the calculation of magnetoelectric coupling and all other properties of a two-phase multiferroic composite consisting of aligned piezomagnetic (or piezoelectric) spheroidal inclusions in a piezoelectric (or piezomagnetic) matrix. Both perfect and imperfect interface conditions are considered. Among the many features of the properties reported is the intriguing magnetoelectric coupling that signifies the "0 þ 0 ! 1" product effect of the multiferroic composite. It is also reported that, due to the piezoelectric-piezomagnetic interaction, the elastic C 44 of the composite can be substantially higher than that of either of the two phases. We have used the theory to calculate the 17 independent material constants: 5 elastic, 3 piezoelectric, 3 piezomagnetic, 2 dielectric, 2 magnetic, and 2 magnetoelectric coefficients of a transversely isotropic BaTiO 3 -CoFe 2 O 4 composite, and show how these magneto-electro-elastic constants depend on the volume concentration, aspect ratio of inclusions, and the interface condition. We conclude by pointing out that a weak interface model is often required to capture the experimentally measured data of a bulk multiferroic composite. IntroductionA multiferroic composite generally refers to a two-phase composite involving two ferroic phases. Most notable among them is the piezoelectric-piezomagnetic composite. The piezoelectric phase, such as barium titanate (BaTiO 3 , or BTO), lead zirconium titanate (PZT), and lead magnesium titanate-lead titanate (PMT-PT), is generally transversely isotropic, and so is the piezomagnetic phase, such as cobalt ferrite (CoFe 2 O 4 , or CFO), Terfenol-D, lanthanum strontium manganite (LSMO), and nickel ferrite (NFO). In such composites, strong coupling tends to develop Y. Wang • G.J. Weng (*) Department of Mechanical and Aerospace Engineering, Rutgers University, New Brunswick, NJ 08903, USA e-mail: yang.wang@rutgers.edu; weng@jove.rutgers.edu © Springer International Publishing Switzerland 2016 S.A. Meguid (ed.), Advances in Nanocomposites, DOI 10.1007/978-3-319-31662-8_8 189 among the elastic, piezoelectric, dielectric, piezomagnetic, and magnetic properties of the constituent phases. These coupling effects can lead to some unique overall properties for the composite. Among the most intriguing features of the coupled effects is the generation of the magnetoelectric coupling coefficients, α 33 and α 11 , which are absent in either the piezoelectric or the piezomagnetic phase alone. This property enables the composite to exhibit magnetization under an electric field, and electric polarization under a magnetic field. It is the so-called "0 þ 0 ! 1" product effect that makes this class of composite so appealing. For instance, in information storage this coupling allows the data to be written electronically and read magnetically; it does not require the generation of a strong local magnetic field to write. In addition, the strong coupling can also make the elastic constant, C 44 , of...

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