Development of Magnetostrictive Fe-Ga and Fe-Pd Thin Films
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Development of Magnetostrictive Fe-Ga and Fe-Pd Thin Films Teiko Okazaki1, Satoru Watanabe1, Norimasa Okanisi1, Toshiro Ono1, Yasubumi Furuya1, Munemi Michigami1, Yasuo Sakisaka1, 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, USA.
ABSTRACT The giant magnetostrictive films exhibit promising device applications for micro-machines and sensor systems due to high response velocity and huge stress created by the magnetostriction. We developed magnetostrictive bimorph-type Fe70Pd30 or Fe83Ga17 (positive magnetostriction)/Al/Ni(negative magnetostriction) thin films by magnetron sputtering. Magnetostriction of these films measured by a bending cantilever beam method has reached 250-300 ppm in the small magnetic field of 1.0 kOe and exhibits little hysteresis. Moreover, the magnetostrictive characteristics do not change under low alternating magnetic field. The magnetoelastic coefficient of these films is 25~30 MPa, which is comparable to the coefficient of the PbTiO3-PbZrO3 system. These metallic sensor/actuator materials are useful for applications in magnetostrictive 2D- scanners and remote-interrogated tire sensors. INTRODUCTION Ferromagnetic shape-memory alloys are an important class of materials that can be used for applications in magnetomechanical devices and sensors[1]. 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[2,3,4]. In a previous study[5,6,7], 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 1000-1800 ppm with a good shape memory effect. 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(1.2µm )/Al/Ni(1.2µm) and Fe83Ga17(1.2µm)/Al/Ni(1.2µm) thin films. We have also made, the magnetostrictive Fe70Pd30/Fe50Co50 multilayers with individual layer thicknesses in the range of 7-21 nm, which were saturated by a relatively low applied magnetic field. The Fe83Ga17 alloy also is known to exhibit giant magnerostriction[8,9]. Magnetostrictive properties for these thin films were investigated under steady or alternating magnetic fields.
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EXPETIMENTAL PROCEDURES The magnetostrictive bimorph-type thin films and nano-structured multilayers[10] were deposited using magnetron sputtering with two targets. The substrate position was rotated in such a way so that materials from the two targets were deposited in an alternating manner, and the multilayers were deposited. The bimorph-type thin films were prepared by depositing Fe70Pd30( or Fe83Ga17) on a surface of Al substrate(50µm in thickness ) and Ni on another with Ar base press
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