MAGNETOOPTICAL KERR-EFFECT STUDY OF AC SUSCEPTIBILITIES IN ULTRATHIN COBALT FILMS

The ac susceptibility of ultrathin Co/Cu(100) films has been investigated in situ under ultrahigh vacuum conditions using the magneto-optical Kerr effect. A conventional Kerr effect setup was combined with an ac-field modulation technique to improve the experimental detection limit. A sensitivity in the range of 10(-8) rad for the Kerr ellipticity has been achieved in the present study. The ac susceptibility chi(ac) of the investigated cobalt films is mainly characterized by a pronounced and sharp maximum as a function of the temperature T. This chi(ac)(T) dependency corresponds to the ferromagnetic-paramagnetic phase transition occurring at the Curie temperature T(c) of the cobalt films, which is also confirmed by experimental observation of the hysteresis behavior, Besides the measurement of Curie temperatures, the experimental technique presented here allows the determination of magnetic properties for ultrathin films even in the paramagnetic regime far above T(c).