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Magnetostructural Phase Transformation and Shape Memory Effect of Fe-added Ni2MnGa Films

Makoto Ohtsuka 1,  Junpei Sekino 2,  Keiichi Koyama 3,  Toshiyuki Takagi 4,  Kimio Itagaki 5

1. Tohoku University, Institute of Multidisciplinary Research for Advanced Materials (IMRAM), 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan
2. Tohoku University, Graduate School of Engineering, 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan
3. Tohoku University, Institute for Materials Research (IMR), 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan
4. Tohoku University, Institute of Fluid Science (IFS), 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan
5. Tohoku University, 2-1-1, Katahira, Aoba-ku, Sendai 980-8577, Japan

Abstract

Ni2MnGa alloy is a multifunctional material with ferromagnetism and shape memory effect (SME). The application of the alloy films as an actuator of micro-machine has been proposed. The SME induced by a magnetic field (MF) will enable the quick response and remote control. In the present study, the magnetostructural phase transformation and SME of Fe-added Ni2MnGa films were investigated. The Fe-added Ni2MnGa films were deposited on poly-vinyl alcohol substrates by a dual magnetron sputtering apparatus using the Fe target (sputtering power: DC 10, 20 W) and the Ni51Mn26Ga23 target (sputtering power: RF 200 W). The composition of the films was Ni52.2Mn24.5Ga20.4Fe2.9 and Ni50.4Mn23.5Ga20.0Fe6.1, respectively. After separating from the substrate, they were heat-treated at 1073 K for 3.6 ks and constraint-aged (CA) at various conditions to make the two-way SME. The Curie temperature was higher than room temperature and its martensitic transformation (MT) temperatures for the films. The X-ray diffraction (XRD) pattern for the CA films was indexed as body centered tetragonal (bct) and 7 layers modulated structure (14M) in the martensitic phase. The reversible two-way SME by the thermal change was confirmed through the MT and its reversion. The gradient of strain-temperature curve, the effective recovering strain and the width of thermal hysteresis were dependent on the CA conditions. The strain-temperature curves shifted to a high temperature region. The MF induced structural phase transformation was evaluated by an XRD apparatus in high MF up to 5 T. It was confirmed the martensitic phase was stabilized by the MF. Furthermore, the SME by the MF was observed around MT temperature on cooling for the films. It was considered that the MF induced SME was appeared by the inducting the martensitic transformation with MF.

 

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Presentation: Oral at E-MRS Fall Meeting 2007, Symposium E, by Makoto Ohtsuka
See On-line Journal of E-MRS Fall Meeting 2007

Submitted: 2007-05-18 09:59
Revised:   2009-06-07 00:44