A magnetic recording disk drive has a bilayer recording medium of a high-anisotropy recording layer and an exchange-coupled antiferromagnetic-to-ferromagnetic (AF-F) transition layer. The transition layer has an AF-F transition temperature (TAF-F) that decreases relatively rapidly with increasing applied magnetic field. Thus the transition layer has a transition field HAF-F(T), which is the applied magnetic field required to transition the material from antiferromagnetic to ferromagnetic at temperature T without the need to heat the layer. At ambient temperature and in the absence of HW, the transition layer is antiferromagnetic and the switching field H0 of the bilayer is just the H0 of the high-anisotropy recording layer, which is typically much higher than HW. In the presence of the write field HW the transition layer transitions from antiferromagnetic to ferromagnetic so that data can be written to the recording by the mere application of the write field HW without the need to heat the transition layer or recording layer. The transition layer may be formed of Fe(RhM), where M is an element selected from V, Mn, Au and Ni.