Unveiling Temperature-Dependence Mechanisms of Perpendicular Magnetic Anisotropy at Fe/MgO Interfaces

The perpendicular magnetic anisotropy at magnetic transition-metal-oxide interfaces is a key element in building out-of-plane magnetized magnetic tunnel junctions for spin-transfer-torque magnetic random access memory (STT MRAM). Size downscaling renders magnetic properties more sensitive to thermal effects. Thus, understanding the temperature dependence of the magnetic anisotropy becomes crucial. In this work, we theoretically address the correlation between the temperature dependence of magnetic anisotropy and magnetization in typical Fe/MgO-based structures. In particular, the possible mechanisms behind the experimentally reported deviations from the Callen and Callen scaling power law are analyzed. At ideal interfaces, first-principles calculations reveal (i) small high-order anisotropy constants compared to first order and (ii) enhanced exchange constants. Considering these two intrinsic effects in the atomistic simulations, the temperature-dependence of the total and layer-resolved anisotropy are found to follow the Callen and Callen scaling power law, thus ruling out an intrinsic microscopic mechanism underlying deviations from this law. Besides, two possible extrinsic macroscopic mechanisms are unveiled, namely the influence of the dead layer, often present in the storage layer of STT-MRAM cells and the spatial inhomogeneities of the interfacial magnetic anisotropy. About the first mechanism, we show that the presence of a dead layer tends to reduce the scaling exponents. In the second mechanism, increasing the percentage of inhomogeneity in the interfacial perpendicular magnetic anisotropy is revealed to decrease the scaling exponent. These results allow us to coherently explain the difference in scaling exponents relating anisotropy and magnetization thermal variations reported in earlier experiments. This is crucial for the understanding of the thermal stability of the storage-layer magnetization in STT-MRAM applications.

Automated summary

This work theoretically addresses the correlation between the temperature dependence of magnetic anisotropy and magnetization in Fe/MgO-based structures. The study reveals possible intrinsic and extrinsic mechanisms that can explain deviations from the Callen and Callen scaling power law. These findings have implications for understanding the thermal stability of storage-layer magnetization in STT-MRAM applications.