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Recent flying heights have been reduced to 10 nm or less. Thermal pole-tip protrusion can further reduce flying clearance by a few nanometers and increase the risk of failure at the head-disk interface. The safety margin of the flying height decreases by a few nanometers due to thermal pole-tip protrusion deformation. This deformation is caused both by mismatched thermal properties of the various materials used in the magnetic head and the write current in the coil. We need to clearly identify the mechanism of this protrusion and accurately estimate its magnitude. In this study, we will numerically and experimentally describe the differences between two boundary conditions under consideration: natural convection off the disk and flying on the disk. Our calculations using the finite element method models quantitatively showed differences in the heat path for the two boundary conditions. Furthermore, we verified that the numerical predictions of thermal pole-tip protrusion were in good agreement with measured results.