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Negative Dynamic Resistance and RF Amplification in Magnetic Tunnel Junctions
Hiroyuki Tomita,Hiroki Maehara,Takayuki Nozaki,Yoshishige Suzuki 한국자기학회 2011 Journal of Magnetics Vol.16 No.2
We report on a numerical calculation study of two new functional properties in magnetic tunnel junctions (MTJs), negative dynamic resistance and RF amplification. The magnetic dynamics in a conventional CoFeB/MgO/CoFeB MTJ with in-plane magnetization was investigated using a macro-spin model simulation. To examine the influence of thermal fluctuations, random external magnetic fields were also included. Using a voltage controlled bias circuit, the negative dynamic resistance was obtained from time averaged Ⅰ-Ⅴ characteristics at both 0 K and 300 K under appropriate external magnetic fields and bias voltages. Using this negative dynamic resistance property, we demonstrated RF amplification with a 100 ㎒ high frequency signal. Sizable RF amplification gain was observed without thermal fluctuation. However, at 300 K, the RF signal was not amplified because low frequency magnetization dynamics were dominant.
Magnetostatic Spin Wave in a Very Thin CoFeB Film Grown on an Amorphous FeZr Buffer Layer
김동석,Kohei Nawaoka,Shinji Miwa,박승영,Yoichi Shiota,유천열,조재훈,이병찬,Yoshishige Suzuki,이긍원 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.67 No.5
The transmission of a magnetostatic spin wave in a very thin CoFeB film (2.3 nm) grown on an amorphous paramagnetic FeZr layer was demonstrated for the first time by using an antenna method with coplanar waveguides. The attenuation length, determined by using the difference in intensities due to a change in the distance between the antennas, was estimated to be 0.7 μm. We discuss why we are able to observe spin-wave propagation in such a thin magnetic layer, taking the low damping constant ( = 0.0027) of the CoFeB films grown on the amorphous FeZr layer and the estimated large group velocity in the CoFeB films into account.