Heat assisted magnetic recording (HAMR) is one of the leading technologies for next generation magnetic recording. Laser heating is utilized in HAMR to achieve magnetic writing of the very high coercivity media. However, the high temperature environment creates several reliability challenges for the head disk interface (HDI). Material transfer within the HDI under HAMR conditions or emulated HAMR conditions has been studied by experiments and simulations. It is found that the material transfer is mainly driven by thermal gradient and mechanical interaction such as head disk contact. In this paper, we designed an experiment to investigate the material transfer from HAMR media to a flying magnetic head. It shows that thermal gradient, more specifically a hotter media and cooler head, is the driving force for the material accumulation on the head. Furthermore, we calibrated the media temperature by a phase change material to identify the critical temperature that triggers the material transfer process. This study is important to understand the smear formation mechanism in HAMR drives.