A method of heat-assisted magnetic recording potentially suitable for probe-based storage systems is characterized. In this work, field-emission current from a scanning tunneling microscope tip is used as the heating source. Pulse voltages of 2–7 V were applied to a CoNi/Pt multilayered film. During heating, various external magnetic fields were applied. Experimental results show that a positive magnetic field increases mark size while a negative field decreases mark size, compared to the case of writing without an external field in which an average mark size of 170 nm was achieved. In addition, a positive field reduces the threshold voltage of writing as well. A synthesized model is built to quantitatively simulate the experimental results. It includes the model of emission current, heat transfer, and dynamics of magnetic domains in the film. Simulation results show that the calculated mark size in various cases is consistent with experimental results. Based on this model, we will be able to figure out the proposals to achieve small marks for the goal of 1 Tbit/in.2 recording density.