Using electrets to design concurrent magnetoelectricity and piezoelectricity in soft materials
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Qian Deng Department of Mechanical Engineering, University of Houston, Texas 77204, USA
Liping Liu Department of Mathematics, Rutgers University, New Jersey, USA; and Department of Mechanical and Aerospace Engineering, Rutgers University, New Jersey 08854, USA
Pradeep Sharmaa) Materials Program, University of Houston, Texas 77204, USA; Department of Mechanical Engineering, University of Houston, Texas 77204, USA; and Department of Physics, University of Houston, Texas 77204, USA (Received 11 June 2014; accepted 14 October 2014)
Piezoelectricity and magnetoelectricity are contradictory properties with a rather limited set of natural (often hard) materials that exhibit both. Composite materials – almost always restricted to hard ones – provide a limited recourse with the attendant limitations of small strains, fabrication challenges among others. In this article, using the concept of electrets, we propose a simple scheme to design soft, highly deformable materials that simultaneously exhibit piezoelectricity and magnetoelectricity. We demonstrate that merely by embedding charges and ensuring elastic heterogeneity, the geometrically nonlinear behavior of soft materials leads to an emergent piezoelectric and magnetoelectric behavior. We find that an electret configuration made of sufficiently soft (nonpiezoelectric and nonmagnetic) polymer foams can exhibit simultaneous magnetoelectricity and piezoelectricity with large coupling constants that exceed the best-known ceramic composites. Moreover, we show that these properties can be tuned with the action of an external field.
I. INTRODUCTION
The ability to control magnetization by an external electric field or polarization by a magnetic field has promising technological applications. These include, among many others, spintronics, nonvolatile memories,1 wireless energy transfer,2 multiple-state memory bits, and memories that can be written electrically and accessed magnetically.3 Similarly, piezoelectricity, where a uniform mechanical strain can induce an electric field and conversely, a uniform electric field can cause mechanical actuation, has also found wide applications, e.g., energy harvesting, artificial muscles, sensing and actuation, advanced microscopy, minimally invasive surgery among others. 4–7 Historically, the magnetoelectric (ME) effect was predicted as early as 1894 while ME materials were not discovered until the 1950s. Since then, extensive research has gone into the quest for a strong ME effect. Disappointingly, the ME effect is intrinsic only in a few a)
Address all correspondence to this author. e-mail: [email protected] DOI: 10.1557/jmr.2014.331 J. Mater. Res., Vol. 30, No. 1, Jan 14, 2015
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single phase materials and the coupling parameter itself (1–20 mV/cm Oe) is too small to be used effectively in several device realizations. Moreover, most of these materials have Curie or Neel temperature far below the room temperature. Growth of good crystals also represented a major challenge since it calls for
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