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Heat assisted magnetic recording (HAMR) has been proposed for the next generation hard disk drive due to its potentially higher storage areal density. In HAMR systems, a laser is focused onto the disk to heat the magnetic storage layer to the Curie temperature. In this paper, a novel method is proposed to study the temperature increase in a perpendicular magnetic recording media. The disk was prerecorded with a uniform single tone magnetic pattern by flying a magnetic head above it and using a magnetic read/write device. The decay of the magnetic pattern resulting from laser heating under different laser power levels was evaluated quantitatively using a magnetic force microscopy. The temperature increase was estimated by use of an Arrhenius-Neel model of thermally activated magnetization. In addition, a 3-D numerical model was created to obtain the disk's thermal response under the laser heating. The thermally erased area was calculated from the temperature distribution based on the numerical results. The calculated erased area was compared with the experimental results from the magnetic images. A good agreement was observed between the experimental and the simulation results. The method should be reliable when used with HAMR media also whenever it becomes available.