We characterize the interlayer coupling and magnetic reversal of antiferromagnetically coupled recording layers. We show that the granular structure and reduced thickness values of the lower layer result in its reversal being strongly thermally activated at room temperature. We also find that the granular structure of the layers produces large dipolar fields which favor antiparallel alignment of the layer magnetizations. These dipolar fields overcome the ferromagnetic regions in the oscillatory coupling as a function of Ru thickness t_(Ru), causing the interlayer coupling to be only antiferromagnetic for t_(Ru)>5 A.
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