| Pacific Rim Symposium on Surfaces, Coatings and Interfaces (PacSurf 2014) | |
| Thin Films | Monday Sessions |
| Session TF+NM-MoE |
| Session: | Nanostructures, Graphene, and Magnetism |
| Presenter: | Masahiro Tobise, Tohoku University, Japan |
| Authors: | M. Takahashi, Tohoku University, Japan M. Tobise, Tohoku University, Japan |
| Correspondent: | Click to Email |
After surprising first report (α”-Fe16N2 phase exhibited a giant saturation magnetization in 1972 as a thin film form [1]), many researches challenged to realize single phase α”-Fe16N2. At 1993, present author et al. established the method in thin film to attain a relatively high volume fraction of α”-Fe16N2 using a reactive sputtering [2]. Precisely determined value of Ms of ≃240 emu/g (≃2.2 T) even though relatively small value compared to initially reported one and value of Ku (≃107 erg/cm3) are very attractive as rare earth free permanent magnet material [3]. But as it was very difficult to form metastable α”-Fe16N2 single phase even in the thin film, it had been believed that the synthesis of a single phase α”-Fe16N2 in bulk form was almost impossible. In 2013, our group established the synthesis procedure of single-phase α”-Fe16N2 nanoparticle for the first time, and reported α”-Fe16N2 exhibit Ms of ≃ 234 emu/g and Ku of ≃107 erg/cm3 [4]. This nanoparticle powder could be synthesized starting from the reduction of Fe-oxides and following nitriding with ammonia gas at temperatures around 145 °C under the very low moisture and oxygen contents less than 1 ppm through the all process. Mössbauer spectra also revealed that the perfect formation of the single phase α” -Fe16N2. In order to improve coercivity through the evaluation of magnetic interaction and the quality of α” -Fe16N2 crystalline, the anisotropy field Hkptc and switching field Hp are determined by rotational hysteresis loss analysis using randomly oriented nanoparticles assembly. Coercivity of nanoparticle assembly consisting of single-phase α”-Fe16N2 formed around 145 °C exceeds 2000 Oe. Normalized coercive force Hc/Hkptc and normalized switching field Hp/Hkptc are about 0.16 and 0.3, respectively. Coercivityhas been improved by surface treatment and reached 3200 Oe at present. Detail on the relationship between these magnetic properties and reversal mechanism is discussed.
References
[1] T.K.Kim and M.Takahashi, Appl . Phys. Lett. 20 , (19 72 ) 492 .
[2] M.Takahashi,H.Shoji, H.Takahashi and T.Wakiyama, IEEE Trans.Mag.29 (1993) 3040
[3] M.Takahashi and H.Shoji, J. Magn . Magn . Mater, 208, ( 2000 ) 145.
[4] T.Ogawa,Y.Ogata,R.Gallage,N.Kobayashi,N.Hayashi,Y.Kusano,S.Yamamoto,K.Kohara,M.Doi,M.Takano and M.Takahashi, Appl. Phys. Express, 6 (2013) 073007