Characterization of heat-assisted magnetic probe recording on cobalt nickel/platinum multilayers

In this PhD project, a method of heat-assisted magnetic recording (HAMR) potentially suitable for probe-based storage systems is characterized. Field emission current from a scanning tunneling microscope (STM) tip is used as the heating source. Pulse voltages of 2--7 V were applied to a CoNi/Pt multilayered film. Identical films fabricated on a bare silicon substrate and an oxidized silicon substrate were applied as the recording medium. Different types of Ir/Pt and W STM tips were used in the experiment. Without the external magnetic field, results show that thermally recorded magnetic marks are formed in the film on silicon substrate, with a nearly uniform mark size of 170 nm when the pulse voltage is above a threshold value. Larger marks were obtained on the film on oxidized silicon substrate. The threshold voltage depends on the material work function of tip. External fields will change the mark size: negative fields lead to smaller marks and positive fields lead to larger marks. Field addition during writing also shows that positive field lowers the threshold write voltage. A model is used to quantitatively simulate our experimental results. It contains three aspects: model of emission current, model of heat transfer in a multilayered structure, and model of magnetic domain. The simulation result agrees well with our experimental results.; Based on the model, the requirements to achieve smaller marks are sharp STM tip and high coercivity granular perpendicular medium fabricated on a high thermal conductivity substrate. Some experiments were done on some high coercivity samples. We achieved the smallest marks as 50 nm. We also tried writing by very sharp STM tips with radius below 10 nm, and unfortunately no marks were written. In order to achieve small marks for the purpose of 1 Terabits/in2 recording density, i.e., mark size of 25 nm, we propose writing on a granular perpendicular medium by applying a 3.5 V voltage between a sharp W STM tip (with tip radius of 50 nm) and the film, with an external field 10% of the saturation magnetization of the film.