Electrical noise in magnetic tunnel junctions due to magneto-structural transitions of CoFeB/MgO interfaces*

Magnetic tunnel junctions (MTJs) play a central role in spintronics research as memory elements, nanoscale microwave oscillators, local magnetic sensors, and neuromorphic network components. Understanding and controlling electric noise in MTJs is a prerequisite for employing them in next-generation applications. Here, we study MTJ nanopillars of 50 nm diameter consisting of CoFeB free layer, MgO tunnel barrier, and CoFe based synthetic antiferromagnet. We observe random telegraph noise which is frequently found in MTJs and yet not fully understood. Varying the temperature in the range of 80-300 K for an MTJ in the parallel state, we encounter anomalous device resistance (steps) attributed [1,2] to magneto-structural phase transitions of iron oxide clusters at the CoFeB/MgO interface. At temperatures of these anomalies, telegraph noise shows a significant increase. This correlation suggests that the oxide clusters have a significant impact on MTJ noise characteristics.