Using structural phase transitions to enhance the coercivity of ferromagnetic films

Heat-assisted magnetic recording (HAMR) is a promising magnetic information storage technology that uses a heating step to lower the coercivity of the recording media and decrease the energy of each writing operation. However, HAMR currently requires temperature increases of several hundred Kelvin, which can cause heat spreading and limit recording rates. Here, we describe a mechanism for tuning the coercivity of ferromagnetic films over small temperature ranges by coupling them to a layer that undergoes a structural phase transition. The method is demonstrated in Ni/FeRh bilayers where Ni layers were deposited either above or below the FeRh metamagnetic transition at 370 K. When the Ni layer is grown at high temperatures, the 1 % FeRh lattice expansion alters the Ni’s crystallographic texture and leads to a 500 % increase in coercivity upon cooling through the FeRh’s metamagnetic transition. Analysis suggests this effect is due to domain wall pinning across grain boundaries with different orientations and strain states. Our work highlights a means to increase the thermal coercivity response of ferromagnetic materials through structural coupling to underlying films, which could enable simplified heatsink designs and expand the selection of materials compatible with HAMR.