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Effects of Fe and Co addition on the magnetoresistance in Ni-Mn-Ga Films
|Kunihiro Koike 1, Makoto Ohtsuka 2, Minoru Matsumoto 3, Adam Yamane 1, Yoshiya Adachi 1, Toshiyuki Takagi 4, Hiroaki Kato 1,5|
1. Graduate school of Science and Engineering, Yamagata University, 4-3-16 Jounan, Yonezawa 992-8510, Japan
Ni2MnGa-type ferromagnetic shape memory alloy is one of the most promising candidates for smart systems. Thin film formation of Ni2MnGa alloy is especially effective for the micro-systems application. Recently, we found that the heat-treated Ni-Mn-Ga-Fe sputtered films with Heusler type crystal structure exhibited both magnetic field induced shape memory effects and magnetoresistance (MR) effects . The MR properties of the films are of interest in view of application to the smart systems. Addition of 3d transition element M such as Co or Fe to the Ni-Mn-Ga films has a potential for expansion of the operating range, because it enhances the Curie temperature TC. Therefore, our purpose is to investigate the effects of Fe and Co addition on the MR in Ni-Mn-Ga films. Films with different Fe and Co composition x were prepared by co-sputtering method. The obtained films were heat-treated at 1073 K for 1 h and aged at 673 K for 1 h in a constrained condition. MR and magnetization σ were measured at fixed temperatures as a function of magnetic fields of up to 15 kOe by using four-point probe and vibrating sample methods, respectively. Martensitic transformation temperature TM was determined by resistance-temperature measurements. With increasing x, σ enhanced for M = Fe, while it reduced for M = Co. These results are consistent with those in bulk alloys . At 300 K, MR value at 15 kOe MR15 was as low as 1%. The value of MR15 was found to be decreased with increasing Fe content. In the case of Co, MR15 increased with x. From these results, it was suggested that an origin of the MR in the present films is dominated by a s-d scattering model .
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Presentation: Poster at E-MRS Fall Meeting 2007, Symposium E, by Kunihiro Koike
See On-line Journal of E-MRS Fall Meeting 2007
Submitted: 2007-05-08 04:15 Revised: 2009-06-07 00:44