Magnetostatic coupling in spin dependent tunnel junctions

Spin dependent tunneling materials have high potential for MRAM, read head, and magnetic field sensor applications because of their superior properties of high sensitivity, low power, and small size. However, for some of these applications, magnetic coupling field between the two magnetic layers has to be reduced in order to take full advantage of these superior properties. A parallel coupling field of 6.7 Oe is obtained by measuring the offset of the minor hysteresis loops of the free layers in typical spin valve like SDT structures. Calculation using Neel's formula and parameters from TEM images yield higher coupling fields than experimentally observed, which suggests that the magnetic roughness is less than what is shown by the contrast in the TEM images. Synthetic antiferromagnet pinned layers help to reduce the parallel coupling, but not enough to null it out. SDT devices were fabricated by RF sputtering and photolithography patterning. On patterned devices, the effective coupling field can be made as small as 0.5 Oe, which is likely due to the cancellation of the Neel coupling and the fringe field coupling.