Angle Dependent Switching of Low Energy Barrier Magnetic Tunnel Junctions

Low energy barrier magnetic tunnel junctions (MTJs) have a stochastically fluctuating magnetoresistance (MR) due to thermally activated reversal of the free layer. Here we describe the angular dependence of switching for MTJs with in-plane magnetization, where the fixed layer consisted of a synthetic antiferromagnet pinned by antiferromagnetic IrMn. 60 x 90 nm devices were patterned by electron beam lithography and ion milling. MR loops were recorded at different field angles to calculate the angle between the free layer magnetization direction and the easy axis (major axis of the ellipse). While easy axis loops showed single sharp switching fields, hard axis loops had gradual changes in resistance due to slowly rotated free layer magnetization. The switching field as a function of the x (easy axis) and y (hard axis) components of the applied field is analyzed where the IrMn layer contributes a cubic-like 4-fold anisotropy field energy term. There is also an asymmetry in the switching field in the ± H_y directions associated with exchange bias. Telegraphing was only observed for a small angular region near the +H_y (hard) axis, where we combined all the mentioned energy terms to determine the two telegraphing positions.