Heat-assisted magnetic recording technology promises increased information storage in hard disk drives by using local laser heating to modify magnetic properties and enable tighter packing of magnetic bits. But current versions of the technology require wide temperature swings and large amounts of heat, which is difficult to confine to the specific areas being written.
To address this issue, Need et al. used a phase transition in thin films of iron rhodium to create a dramatic change in the coercivity of an adjacent ferromagnetic nickel layer. Coercivity is a measure of how difficult it is to switch the direction of a magnet and how much energy is required to rewrite a bit of information, to switch it from 1 to 0 or vice versa.
Above the phase transition, nickel is magnetically coupled to the underlying ferromagnetic iron rhodium and the system has low coercivity and easily writeable. Interestingly, when nickel was grown at high temperatures above the phase transition, cooled down and measured at room temperature, the coercivity was five times larger, which is beneficial for thermal stability. Because the underlying iron rhodium phase transition occurs over a small temperature range, the researchers were able to generate this five-fold change in coercivity over a temperature window of 50 °C, which is considerably smaller than that currently required in heat-assisted magnetic recording.
Their analysis suggests that any material undergoing a structural phase transition could be useful for thermally tuning the coercivity of ferromagnets. The authors plan to explore other types of phase transitions and verify that the process works in perpendicular magnetic recording media, a leading class of magnetic materials currently used in magnetic information storage.
Source: “Using structural phase transitions to enhance the coercivity of ferromagnetic films,” by Ryan F. Need, Josh Lauzier, Logan Sutton, Brian J. Kirby, and Jose de la Venta, APL Materials (2019). The article can be accessed at https://doi.org/10.1063/1.5118893.