Abstract
Storing information in magnetic recording technologies requires careful optimization of the recording media’s magnetic properties. For example, heat-assisted magnetic recording (HAMR) relies on a prerecording heating step that momentarily lowers the coercivity of the ferromagnetic recording media, and thereby decreases the energy expenditure for each writing operation. However, this process currently requires local temperature increases of several hundred Kelvins, which in turn can cause heat spreading, damage the write head, and limit recording rates. Here, we describe a general mechanism for dramatically tuning the coercivity of ferromagnetic films over small temperature ranges, by coupling them to an adjacent layer that undergoes a structural phase transition with large volume changes. The method is demonstrated in Ni/FeRh bilayers where the Ni layer was deposited at 300 K and 523 K, above and below the FeRh metamagnetic transition at 370 K. When the Ni layer is grown at high temperatures, the 1% FeRh lattice expansion relative to room temperature alters the Ni’s crystallographic texture during growth and leads to a 500% increase in coercivity upon cooling through the FeRh’s metamagnetic transition. Our analysis suggests this effect is related to domain wall pinning across grain boundaries with different orientations and strain states. This work highlights the promise of thermally tuning the coercivity of ferromagnetic materials through structural coupling to underlying films that could enable simplified heatsink designs and expand the selection of materials compatible with HAMR.
Highlights
Engineering the coercivity of magnetic materials is critical to improving the stability and efficiency of magnetic recording media.1–4 A central trade-off is that while larger coercive fields provide increased protection of information against thermal fluctuations and demagnetizing fields, they increase the energy required to switch a bit
Our analysis suggests that this coercivity enhancement is a general phenomenon of FM films structurally coupled to materials with first-order phase transitions, and may provide an opportunity to tailor the properties of numerous technologically relevant magnetic materials
In Ni/V2O3, it was concluded that the coexistence of metallic and insulating V2O3 phases with different in-plane lattice constants during the metal-to-insulator transition (MIT) creates magnetic domains with different strain states in the overlying Ni layer
Summary
Engineering the coercivity of magnetic materials is critical to improving the stability and efficiency of magnetic recording media. A central trade-off is that while larger coercive fields provide increased protection of information against thermal fluctuations and demagnetizing fields, they increase the energy required to switch a bit. Reducing the coercivity of common magnetic storage media can require local temperature increases of several hundred Kelvins.. Reducing the coercivity of common magnetic storage media can require local temperature increases of several hundred Kelvins.6,7 These large heat loads create problems confining the heat laterally to enable high areal bit density, removing the heat quickly to achieve a rapid thermal response and recording rate, and protecting the write head from thermal degradation over time.. While it is possible to address these issues individually through improved heatsink designs or better barrier coatings, finding new ways to modify magnetic coercivity and lower switching fields can circumvent these problems altogether.. Attractive are methods to increase a material’s thermal coercivity response [i.e., HC(T)], which can reduce the heat load required and directly address the source of HAMR’s heat management issue
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