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We investigated the effect of using a synthetic ferrimagnetic (SyF) free layer in MgO-based magnetic tunnel junctions (MTJs) on current-induced magnetization switching (CIMS), particularly for application to spin-transfer torque random access memory (SPRAM). The employed SyF free layer had a Co40Fe40B20/Ru/Co40Fe40B20 and Co20Fe60B20/Ru/Co20Fe60B20structures, and the MTJs (100 × (150-300) nm²) were annealed at 300 °C. The use of SyF free layer resulted in low intrinsic critical current density (Jc0) without degrading the thermal-stability factor (E/kB T, where E, kB, and Tare the energy potential, the Boltzmann constant, and temperature, respectively). When the two CoFeB layers of a strongly antiferromagnetically coupled SyF free layer had the same thickness, Jc0) was reduced to 2-4 × 106 A/cm². This low Jc0) may be due to the decreased effective volume under the large spin accumulation at the CoFeB/Ru. The E/kBT was over 60, resulting in a retention time of over ten years and suppression of the write current dispersion for SPRAM. The use of the SyF free layer also resulted in a bistable (parallel/antiparallel) magnetization configuration at zero field, enabling the realization of CIMS without the need to apply external fields to compensate for the offset field. [ABSTRACT FROM AUTHOR]