Abstract
We have investigated the effect of an ultra-thin Ta insertion in the CoFeB (CoFeB/Ta/CoFeB) free layer (FL) on magnetic and tunneling magnetoresistance (TMR) properties of a CoFeB-MgO system with perpendicular magnetic anisotropy (PMA). It is found that the critical thickness (tc) to sustain PMA is doubled (tc = 2.6 nm) in Ta-inserted CoFeB FL as compared to single CoFeB layer (tc = 1.3 nm). While the effective magnetic anisotropy is found to increase with Ta insertion, the saturation magnetization showed a slight reduction. As the CoFeB thickness increasing, the thermal stability of Ta inserted structure is significantly increased by a factor of 2.5 for total CoFeB thickness less than 2 nm. We have observed a reasonable value of TMR for a much thicker CoFeB FL (thickness = 2-2.6 nm) with Ta insertion, and without significant increment in resistance-area product. Our results reveal that an ultra-thin Ta insertion in CoFeB might pay the way towards developing the high-density memory devices with enhanced thermal stability.
Highlights
Spin-transfer-torque magnetic random access memory (STT-MRAM) is a promising generation memory technology due to its non-volatility, high speed, low power consumption as well as potentially unlimited endurance.[1,2,3,4,5,6,7] STT-MRAM cell stores data by switching the orientation of free layer (FL) magnetization with respect to that of reference layer (RL) of its constituent magnetic tunnel junction (MTJ)
A detailed magnetic property study showed that the maximum thickness to sustain perpendicular magnetic anisotropy (PMA) is increased to 2.6 nm in Ta inserted CoFeB FL as compared to the 1.3 nm single CoFeB layer
Due to the increased CoFeB thickness, the is significantly improved by a factor of 2.5 for thinner CoFeB (t < 2 nm) with an optimized Ta = 250 ◦C which indicates that much smaller MTJ devices can be developed while maintaining a high
Summary
Perpendicular-anisotropy CoFeB-MgO magnetic tunnel junctions with a MgO/CoFeB/Ta/ CoFeB/MgO recording structure Applied Physics Letters 101, 022414 (2012); https://doi.org/10.1063/1.4736727 The design and verification of MuMax[3] AIP Advances 4, 107133 (2014); https://doi.org/10.1063/1.4899186
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