Experimental Study Of Laser-Induced Protrusion In Heat-Assisted Magnetic Recording

In heat-assisted magnetic recording (HAMR), a laser is introduced to create a hot spot on the media and locally heat the magnetic layer to its Curie temperature. Besides the optical power that the laser provides to the media, thermal energy diffuses inside the slider and induces an extra protrusion, which is called laser-induced protrusion (LIP). The LIP needs to be considered and compensated during flying in the HAMR conditions. In this study, we focus on long timescale (milliseconds) of laser heating during the flying condition. When the laser is switched from OFF to ON, the touchdown power, indicated by an acoustic emission (AE) sensor, decreases due to spacing loss and the touchdown power change (DTDP) is used as the measure of the LIP. A component-level spinstand stage for HAMR heads and media is used to study the LIP as a function of laser-on time, laser current and linear velocity. Our experimental results show that it takes around 20 ms for the LIP to reach steady state and the protrusion size is proportional to the square of laser current. As the operating linear velocity increases from 12 m/s to 24 m/s, the LIP decreases by approximately 52%.