Temperature-Dependent Exchange Splitting of a Surface State on a Local-Moment Magnet: Tb(0001)

We have investigated the temperature-dependent binding energies of the exchange-split Tb(0001) surface state by means of scanning tunneling spectroscopy. At T0ex0ex=0ex0ex16K the majority and minority part of the surface state exhibit a binding energy of -135±8meV and +430±15meV, respectively. Both peak positions shift with increasing temperature and continuously decrease the exchange splitting down to 200 meV at 260 K, i.e., 30 K above the bulk N\'eel temperature TNB. This result is explained in terms of a decrease of helical short-range spin order with increasing temperature above TNB.