Frequency selection for magnetization switching in spin torque magnetic memory

The change of magnetization states by spin transfer torque brought momentum to research on magnetic random access memory (MRAM), however, there is still a need for improvement of memory performances. The conventional multi-bit per cell (MBPC) scheme has the potential of increasing the storage capacity of MRAM but the overwritability issue remains the major drawback of this scheme. In fact, for systems with more than one free layer, the low anisotropy layer can have its magnetization reversed during the writing on the higher anisotropy one. To access each free layer independently, a spin torque oscillator with an optimal frequency is proposed to assist the magnetization switching. This study reveals that the free layer magnetization can be reversed through a selection of a frequency value which depends on its intrinsic magnetic properties. This resonance phenomenon based on frequency selection and spin transfer torque effect can be used for writing in the MBPC scheme without undesirable overwriting. A spin torque oscillator with an optimal frequency integrated with a conventional magnetic tunnel junction could be the platform of future magnetic memory. (paper)