A thermally assisted write head having a plasmonic heating device. The plasmonic heating device has a plasmonic antenna located at an air bearing surface of the thermally assisted write head. The plasmonic antenna is constructed of an alloy that is sufficiently hard to withstand the processes such as ion milling and chemical mechanical polishing used to construct the plasmonic antenna. The plasmonic antenna is preferably constructed of AuX, where X is Cu, Ni, Ta, Ti, Zr or Pt having a concentration less than 5 atomic percent.