Influence of dot size and annealing on the magnetic properties of large-area L1-FePt nanopatterns

Abstract

Hard magnetic L10-FePt nanopatterns composed of a regular arrangement of single-domain nanodots with out-of-plane texture and dot sizes between 40 nm and 100 nm have been fabricated over an area of 4 mm2 from continuous epitaxially grown L10-Fe51Pt49 films by ultraviolet nanoimprint lithography combined with inductively coupled plasma reactive Ar-ion etching. Whereas the dot size within the dot size range investigated according to superconducting quantum interference device (SQUID) magnetometry has been found to have no significant influence on the magnetic properties, the magnetic properties and magnetization reversal mechanism significantly depend on the structural morphology and shape of the nanodots which change during a post-annealing process at elevated temperatures according to high-resolution TEM investigations from crown-shaped dots with a gradually deteriorated surface region of several nm to curved dots of pure L10-FePt. The different morphology of the nanodots results for the as-etched state in smaller coercivity values (1.30 T – 1.66 T at RT) and a less strong temperature dependence of the coercivity in the temperature range of 40 K – 350 K compared to the post-annealed state (4.37 T – 4.56 T at RT). As the morphology of the as-etched dots has been found to resemble the morphology of a phase graded composite particle magnetization reversal can be attributed to a domain wall induced process (microstructural parameter α < 0.15). In contrast, for the post-annealed dots of pure L10-FePt magnetization reversal takes place by a uniform nucleation process (microstructural parameter α > 0.79).