High aspect ratio free standing ZnO-magnetostrictive mesoscale cylindrical magnetoelectric core shell composite
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High aspect ratio free standing ZnO-magnetostrictive mesoscale cylindrical magnetoelectric core shell composite S. Kaps,1 Y. K. Mishra,1 V. Hrkac,2 H. Greve,3 L. Kienle,2 E. Quandt,3 R. Adelung1* 1
Functional Nanomaterials, Institute for Materials Science, University of Kiel, Kaiserstrasse 2, D-24143, Kiel, Germany 2 Synthesis and Real Structure, Institute for Materials Science, University of Kiel, Kaiserstrasse 2, D-24143, Kiel, Germany 3 Inorganic Functional Materials, Institute for Materials Science, University of Kiel, Kaiserstrasse 2, D-24143, Kiel, Germany ABSTRACT Optimizing magnetic field sensors made by piezoelectric-magnetostrictive composites is a trade off between several parameters. Whereas large structures will cause in principle high electrical currents the mechanical coupling will lead to shear losses and therefore limit the sensitivity of the sensor and make it impossible to measure small magnetic fields. In very small structures the shear losses will decrease but the imperfections in the interfaces become more important and the typically small currents will be disturbed by, e.g., surface conductivity of the piezoelectric material and are thus difficult to measure. The best compromise is a mesoscale sensor which has relatively small losses due to shearing but still high enough electrical currents to work as a good sensor. We will present a setup which allows the use free standing ZnO micro rods as piezoelectric core material which are surrounded by a magnetostrictive layer. Since no clamping is necessary the expansion and contraction of the material is not hindered by a matrix material. The tuning of the relative layer thicknesses can be easily optimized by changing the thickness of the magnetostrictive layer so that an optimum can be achieved for different ZnO micro rods. For the growth of the ZnO a newly developed process will be presented which allows the growth of a large variety of single crystals with different aspect ratios up to needles with several millimeters in length. INTRODUCTION Piezoelectric and magnetostrictive materials find interesting technological applications ranging from different electronic devices to highly sophisticated sensors [1]. For a possible ME sensor the crystalline quality of the piezo as well as the interface between magnetostrictive and piezoelectric material are very important and presented here. The appropriate combination of materials with a high magnetostrictive susceptibility and high piezoelectric coefficients should provide large magneto-electric (ME) effects. In the past these ME composites were realized by gluing a piezoelectric material on a magnetostrictive body, e. g., Terfenol-D/PVDF [2] or Terfenol-D/PMN-PT [3]. Nowadays the availability of thin film technology and the improvements in small scale engineering can be used to fabricate ME composites on desired small scales without using any adhesive [4]. One common problem when designing ME sensors based on thin film technology is clamping of the substrate which causes a reduction in the ME effect. A ME
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