Temperature gradients influencing the hysteresis of ferromagnetic nanostructures (Vol. 49, No. 1)

(a) Nanowire device used for magneto-optical Kerr effect (MOKE) measurements. (b) Normalized coercive fields HC/HC,ΔT=0K for Co39Ni61 and Fe15Ni85 nanowires as a function of the temperature gradient ΔT. Increasing HC with increasing ΔT for Co39Ni61 nanowires contradict the basic concept of heat assisted magnetization reversal (HAMR).

For future data storage technology, in which downscaling of magnetic bit unit sizes is crucial, heat-assisted magnetic recording (HAMR) is one key technology to ensure the writability for magnetic bits. It relies on a laser heating pulse to lower the coercive field HC of the magnetic bit unit. Here, we investigated the temperature- and temperature gradient-dependent switching behaviour by HC measurements of individual, single-domain CoNi and FeNi alloy nanowires via measurements of the magneto-optical Kerr effect. While the switching field generally decreased under isothermal conditions at elevated temperatures, temperature gradients (ΔT) along the nanowires led to an increased switching field up to 15 % for ΔT = 300 K in Co39Ni61 nanowires. We attribute this enhancement to a stress-induced contribution of the magneto-elastic anisotropy that counteracts the thermally assisted magnetization reversal process. Our results demonstrate that a careful distinction between locally elevated temperatures and temperature gradients has to be made in future HAMR devices.

A.-K. Michel and 12 co-authors, Temperature gradient-induced magnetization reversal of single ferromagnetic nanowires, J. Phys. D: Appl. Phys. 50, 494007 (2017)