We report magnetic coupling behaviors in M-type Sr-hexaferrite (SrM)/Fe bilayers. A magnetic hardening of a Fe layer by a SrM layer is clearly observed when the thickness of the Fe layer is less than 3 nm, and the magnetically hardened 3 nm Fe layer shows a coercivity of SrM layer. The magnetic hardening of Fe layer can be switched into a magnetic softening of SrM layer in SrM/Fe bilayer when an interfacial crystallinity of Fe layer is improved by vacuum annealing at 250-300 degrees C. The controllable magnetic hardening and softening in SrM/Fe bilayer could be promising for both hard magnetic and soft magnetic applications. (C) 2015 Elsevier B.V. All rights reserved.