The effect of external magnetic field on mark size during field emission assisted magnetic probe recording on CoNi/Pt multilayers

In this work, we characterize a heat-assisted magnetic recording process potentially suitable for proposed probe-based storage systems. A scanning tunneling microscope (STM) is used to locally heat a uniformly magnetized perpendicular recording medium via field emission current. The recording medium is a 30 nm thick CoNi/Pt multilayer film (H_C = 100 kA/m [1.2 kOe], M_S = 360 kA/m) with a 23 nm thick Pt seedlayer, fabricated on a bare Si substrate. Voltage pulses were applied between STM tip (made of Ir/Pt) and the medium to write marks with external magnetic field applied. A magnetic force microscope (MFM) is used to image marks. Mark size was measured as the FWHM of MFM phase signal. Experimental results show that mark size increases with increasing positive field and decreases with increasing negative field. A model is quantitatively simulate our experimental results and we are able to predict tip and medium configurations and applied powers that should permit marks appropriate for recording at 1 Tbit/in² and beyond.