Multistate spin-transfer-torque random access memory
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Spin-transfer-torque random access memory (STT-RAM) is an emerging non-volatile memory technology that stores information as the relative alignment of two ferromagnets in a magnetic tunnel junction stack. Due to high scalability, speed and endurance STT-RAM is being considered as a promising candidate for future universal memory. To improve storage density various multi-state configurations have been proposed for STT-RAM. Previously, using micromagnetic simulations, it was shown that shape anisotropy of a cross-shaped ferromagnet can be used to achieve multi-state operation in a STT-RAM bit. In this work, we attempt to demonstrate the multi-state operation of such cross-shaped ferromagnet experimentally. We have explored different approach to fabricate cross-shaped magnetic tunnel junctions. Using magnetic force microscopy we demonstrate equilibrium magnetization states of a patterned cross-shaped ferromagnet. Challenges and future perspectives have been discussed.