2015 Fiscal Year Annual Research Report
| Project/Area Number |
15J03637
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| Research Institution | Tohoku University |
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Principal Investigator |
曹 洋 東北大学, 工学系研究科, 特別研究員(DC2)
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| Project Period (FY) |
2015-04-24 – 2017-03-31
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| Keywords | Co-HfN / Co-AlF / Nanogranular films / High-frequency device / Magneto-dielectricity |
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| Outline of Annual Research Achievements |
Nanogranular films with intriguing fucntional properties are gathering great attention for its application in transformers, inductors and magnetic field sensors.I succeed to deposite the CoHfN nanogranular films by co-sputtered Co and HfN target. Films consist of amorphous HfN matrix and crystalline Co nanogranules, which have growth-induced perpendicular magnetic anisotropy (PMA). The PMA films have coercivity (Hc)of 100 Oe, magnetic saturation field (Hs) of 1200 Oe. The permeability is approximately 40, keeping constant up to 2 GHz. Therefore, the Co-HfN nanogranular films have high potential application for devices with in-plane isotropic response.Next,in order to suppress the Co columnar structure and reduce the Hc (＜20 Oe), I tried to prepare the multilayer films. The films were composed of the crystalline Co and amorphous HfN layers. The Co/HfN films show soft magnetic properties with Hc of 2 Oe and Hk of 30 Oe with high permeability of 250, keeping constant up to 1.6 GHz.
Moreover, I succeed to prepare Co26-Al18F56 nanogranular film, which is consisted of nanometer-sized Co granules distributed in the AlF amorphous ceramic matrix. The dark dots indicate the Co granule with the granule size of around 2 nm. The magnetization curves exhibit super-paramagnetic properties over a wide range of Co concentration. The dielectric properties (ε’) are enhanced by increasing the Co content, owning to the increasing granule pairs of the films. The tunneling magneto-dielectric (TMD) effect was observed in Co26-Al18F56 film. The (ε’H-ε’0)/ε’0 is about 0.6 % at 500 kHz.
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| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
I have found the growth-induced perpendicular magnetic anisotropy in Co-HfN nanogranular films. Besides, I have tried to suppress the perpendicular anisotropy by constructing the multilayer films. (InterMag 2015, Best poster award).While,little is known about how to deliberately control the perpendicular anisotropy and then controllable high frequency application.Research on the controllable anisotropy is of great significance for fundamental research.
In 2014, our research group discovered the magneto-dielectric effects in FeCo-MgF insulating nanogranular films within the granule range of 10-40%, which have potential application in magnetic field sensors and impedance-tunable devices. Such new phenomenon is attributed to the spin-dependent quantum mechanical tunneling between granule pairs. I have successfully realized the magneto-dielectric properties by developing co-separate sputtering method.(日本金属学会2016年春期講演大会優秀発表賞). While such effects is still low, future research will be focused on improving the magneto-dielectric response.
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| Strategy for Future Research Activity |
I for the first time propose the discontinuous granular films,which the Co granules are dispersed in HfN matrix. Also, the HfN matrix was used as interlayer for controlling the perpendicular magnetic anisotropy. Future research will focus on constructing the discontinuous granular films with controllable perpendicular magnetic anisotropy.
Regarding to the low magnetic-dielectric effects, I propose a two-dimensional structure to enhancing such effects. The effect of Co layer and AlF layer on magneto-dielectric properties will be systemically studied.
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