Magnetization switching behavior of exchange-coupled bilayer nanodots characterized by magneto-optical Kerr effect

Abstract

We investigated the magnetization switching behavior of exchange-coupled bilayer nanodots consisting of a soft magnetic Ni81Fe19 (permalloy; Py) layer and a perpendicularly magnetized L10-FePt layer by measuring the polar magneto-optical Kerr effect (MOKE). A MOKE system having a 2-μm-diameter laser spot was used, which detected the signal from around 20 nanodots of 200 nm in diameter. The measured polar MOKE loops exhibited a two-step behavior attributable to each magnetization reversal process of the Py and L10-FePt layers, allowing us to evaluate the switching field (Hsw) of L10-FePt from the MOKE loop. Under the application of both a static magnetic field and an rf magnetic field (hrf), the nanodots showed a clear Hsw reduction with characteristic hrf frequency dependence. This Hsw reduction is well interpreted as a behavior of spin wave-assisted magnetization switching. We also discuss the influence of the Py layer thickness on spin wave-assisted Hsw reduction.