Bimorph-type Magnetostrictive Actuator/Sensor Thin Films
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Bimorph-type Magnetostrictive Actuator/Sensor Thin Films Teiko Okazaki1, Norimasa Okanisi1, Yuki Miura1, Munemi Michigami, Yasubumi Furuya1, Ichiro Takeuchi2 and Manfred Wuttig2 1
Faculty of Science and Technology, Hirosaki University, Hirosaki 036-8561, Japan.
2
Department of Materials Science and Engineering, University of Maryland, College Park, MD
20742-2115, USA. ABSTRACT Giant magnetostrictive Fe-Pd and Fe-Ga thin films are expected as actuator/ sensor materials with high respective velocity and huge stress created by the magnetostriction. In order to develop magnetostrictive material induced by low magnetic field, we investigated bimorph-type magnetostrictive (positive magnetostriction / substrate / negative magnetostriction) thin films, that is, Fe-Pd(1, 3µm) or Fe-Ga(1, 3µm )/substlate /Ni(1, 3µm) by magnetron sputtering system. The substrate is Al(50µm) or kapton foil (125µm). Displacement of a upper part of these films was measured using an optical lever method. The displacement of the Fe70-Pd30(3µm )/ Al(50µm)/Ni(3µm)film ( length is 20 mm) was 280 µm under low DC magnetic field of 500 Oe and exhibits little hysteresis. These magnetostrictive properties are maintained under low alternating magnetic field. Moreover, the displacement of the film at the resonance frequency exhibits a peak and reached to 1.4 mm. The bimorph-type magnetostrictive thin film is useful for application in micro device as micro-pomp. INTRODUCTION Ferromagnetic shape-memory alloys are an important class of materials that can be used for applications in magnetomechanical devices and sensors. Research in this field has been focused on Fe-Pd and Ni2MnGa due to the large strains induced in these systems by an external magnetic field[1]. In a previous study[2], we showed that polycrystalline Fe70.4Pd29.6 thin foil prepared by the rapid-solidified melt-spinning method display a fine columnar microstructure with strong [100]-oriented texture and exhibit giant magnetostriction of 1000 ppm with a good shape memory effect. Moreover, we reported that rapid-solidefied melt-spun Fe83Ga17 foil shows large magnetostriction of 270 ppm[3].
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However, in order to achieve saturation magnetostriction, large magnetic field of 10 kOe is required. In this study, using magnetron sputtering, we have fabricated bimorph-type magnetostrictive Fe70Pd30 (1.2, 3µm) / substrate / Ni (1.2, 3µm) and Fe83Ga17 (1.2, 3µm) / substrare / Ni (1.2, 3µm) thin films. These substrates are Al(50µm) or kapton foil (125µm). Magnetostrictive properties for these thin films were investigated under DC and alternating magnetic fields. EXPETIMENTAL METHOD The magnetostrictive bimorph-type thin films were deposited using magnetron sputtering with Fe70Pd30, Fe85Ga15 and Ni targets. We pasted four chips of Fe70Ga30 alloy on the Fe85Ga15 target because the Ga content of the film sputtered with the target decreases. The bimorph-type thin films were prepared by depositing Fe70Pd30 ( or Fe83Ga17) on a surface of substrate and Ni on another with Ar base pre
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