The Gilbert damping of ferromagnetic materials is arguably the most importantbut least understood phenomenological parameter that dictates real-timemagnetization dynamics. Understanding the physical origin of the Gilbertdamping is highly relevant to developing future fast switching spintronicsdevices such as magnetic sensors and magnetic random access memory. Here, wereport an experimental study of temperature-dependent Gilbert damping inpermalloy (Py) thin films of varying thicknesses by ferromagnetic resonance.From the thickness dependence, two independent contributions to the Gilbertdamping are identified, namely bulk damping and surface damping. Of particularinterest, bulk damping decreases monotonically as the temperature decreases,while surface damping shows an enhancement peak at the temperature of ~50 K.These results provide an important insight to the physical origin of theGilbert damping in ultrathin magnetic films.
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