A magnetic microstructure comprising (i) a magnetic storage layer having a magnetic easy axis perpendicular to a film plane of the storage magnetic layer; (ii) a magnetic assist layer having a magnetic easy axis in the film plane; and (iii) a phase transition interlayer between the magnetic storage layer and the magnetic assist layer. The phase transition layer comprises a material, such as FeRh, that switches from antiferromagnetic at ambient to ferromagnetic at a transition temperature that is greater than ambient, but below the Curie temperature. When the phase transition interlayer is in antiferromagnetic phase, there exists little magnetic coupling between the storage and assist layers. When the interlayer changes to ferromagnetic phase, the interlayer couples the magnetic moments of the storage and assist layer ferromagnetically. If the anisotropy field-thickness product of the two layers is similar and the coupling is sufficiently strong, the effective magnetic anisotropy of the storage layer and the assist layer essentially vanishes. That way, the required write field at the recording temperature needs only to be a few percent of the ambient anisotropy field of the storage layer.