Magnetic-Field-Induced Strain of Fe-based Ferromagnetic Shape-Memory Alloy in a Pulsed Magnetic Field
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1050-BB05-05
Magnetic-Field-Induced Strain of Fe-based Ferromagnetic Shape-Memory Alloy in a Pulsed Magnetic Field Takuo Sakon1, Takashi Fukuda2, Hiroyuki Nojiri3, and Tomoyuki Kakeshita2 1 Faculty of Engineering and Material Research, Akita University, Tegatagakuen-machi 1-1, Akita City, 010-8502, Japan 2 Graduated School of Engineering, Osaka University, Suita City, 565-0871, Japan 3 Institute for Materials Research, Tohoku University, Sendai, 980-8577, Japan ABSTRACT The magnetic field-induced strain (MFIS) of the martensite metallic compound Fe-31.2% Pd (at.%) and Fe3Pt were studied in a pulsed magnetic field using the capacitance method at low temperatures in a martensitic phase, which is much lower than the martensitic transformation temperature TM. After zero field cooling, pulse magnetic field was applied parallel to [001]p axis. Large MFIS has been measured. The value of the MFIS ∆L/L is 0.4 % expansion, 1.7 % compression, respectively. When the magnetic field was decreased, the recovery of the strain of Fe3Pt was observed. At the 2nd shot, the strain of about 0.6 % was observed. It means that MFIS occurs even in short-pulse magnetic fields. INTRODUCTION Recently, ferromagnetic shape memory alloys (FSMA), for example, Ni-Mn-Ga alloy , disorderd Fe-Pd and Fe3Pt alloys have attracted much interest due to the giant magnetic fieldinduced strain (MFIS). These alloys are candidates for highly functional materials for use in micro machine engineering [1,2]. The most well-known example of MFIS is that of Ni-Mn-Ga alloy, which is the first example of MFIS and which was discovered by Ulakko and co-workers [3,4]. Disordered Fe-Pd and ordered Fe3Pt alloys also exhibit large MFISs [5]. The mechanism of this strain is thought to be same as the mechanism of the strain in Ni-Mn-Ga alloy as mentioned above. The Fe-Pd and Fe3Pt alloys are ferromagnetic alloys and have cubic crystal structures in a parent phase. The crystal structure is A1-type for Fe-Pd and L12 type for Fe3Pt. Both alloys exhibit thermoelastic martensitic transformations to tetragonal structures (f.c.t. martensite) [6, 7]. Kakeshita et al. carried out an experimental study of MFIS of Fe-31.2%Pd (at.%) and Fe3Pt alloys under steady magnetic field using a superconducting magnet [8-10]. The martensitic
transformation temperature TM of the Fe-31.2%Pd (at.%) is approximately 230 K, which was determined by the magnetic susceptibility measurement. A very large MFIS was observed at 77 K, which is much lower than TM. The saturated strain is about 3.0 % along the [001]p direction with application of magnetic field along the [001]p direction (the symbol "p" indicates the parent phase). As for the Fe3Pt alloy, TM was found to be 85 K by the magnetic susceptibility measurement [10,11]. When a magnetic field is applied along the [001]p direction at 4.2 K, the sample contracts along this direction due to the rearrangement of the variants. The saturated strain is about 2.3% at 4.2 K. In association with this contraction, the fraction of the variant whose easy axis (c-axi
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