| Summary: | Spin-transfer torque magnetoresistive random access memory (STT-MRAM) technology is considered to be the most promising nonvolatile memory (NVM) solution for high-speed and low power applications. Dual MgO-based composite free layers (FL) have driven the development of STT-MRAMs over the past decade, achieving data retention of 10 years at the cost of higher write power consumption. In addition, the need for tunnel magnetoresistance (TMR)-based read schemes limits the flexibility in materials beyond the typical CoFeB/MgO interfaces. In this study, we propose a novel spacerless FL stack comprised of CoFeB alloyed with heavy metals such as tungsten (W) which allows effective modulation of the magnet properties (<i>M<sub>s</sub></i>, <i>H<sub>k</sub></i>) while retaining compatibility with MgO layers. The addition of W results favours a delayed crystallization process, in turn enabling higher thermal budgets up to 180 min at 400 °C. The presence of tungsten reduces the total FL magnetization (<i>M<sub>s</sub></i>) but simultaneously increasing its temperature dependence, thus, enabling a dynamic write current reduction of ~15% at 2 ns pulse widths. Reliable operation is demonstrated with a WER of 1 ppm and endurance >10<sup>10</sup> cycles. These results pave the way for alternative designs of STT-MRAMs for low power electronics.
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