Temperature dependence of interlayer coupling between perpendicular magnetic [CoFeB/Pd] multilayers: Influence of interfacial CoFeB layer

Abstract

Temperature dependence of interlayer coupling field in the perpendicular antiferromagnetic structure of [Pd/CoFeB]2/Pd/CoFeB(tCFB)/Ru(tRu)/CoFeB(tCFB)/Pd/[CoFeB/Pd]2 is found to be sensitive to tCFB, showing various non-monotonic behaviors. The coupling strength increases with tCFB, reaching bulk-like value of up to 0.28 erg/cm2 at room temperature as tCFB is over 0.6 nm. We attribute the phenomena to interfacial effects, including lowered Curie temperature in ultrathin CoFeB layers and increased effective dead layer thickness. The coupling peak position of tRu also shifts with temperature and tCFB, corresponding to variations in dead layer thicknesses. These effects should be considered when designing practical devices employing perpendicular synthetic antiferromagnetic structures.