Conductive atomic force microscopy of small magnetic tunnel junctions with interface anisotropy

Magnetic anisotropy at the interface between a thin metallic ferromagnet and an insulating oxide layer has been used to make devices with voltage-controlled switching. Sharp switching thresholds have previously been reported for devices below 100 nm, but questions remain about the size dependence of the switching thresholds and the stability with respect to thermal fluctuations. Here a series of CoFeB (1.5 nm)/MgO (2 nm)/CoFeB (0.8 nm) magnetic tunnel junctions (MTJs) with interface anisotropy were characterized using conductive atomic force microscopy (CAFM) to measure their resistance as a function of the perpendicular magnetic field and bias voltage. With a lithographically patterned MTJ, there are two new features, relative to prior work applying this technique to nanoparticles. First, both magnetic layers have a known crystallo-graphic orientation, which in this case leads to perpendicular magnetic anisotropy and increased squareness in the hysteresis loops. Second, features varying over a wide range of device diameters but the same tunnel barrier thickness have been prepared, enabling the systematic determination of size-dependent properties.