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

The ac susceptibility of ultrathin Co/Cu(100) films has been investiga ted in situ under ultrahigh vacuum conditions using the magneto-optica l Kerr effect. A conventional Kerr effect setup was combined with an a c-field modulation technique to improve the experimental detection lim it. 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 pronounc ed and sharp maximum as a function of the temperature T. This chi(ac)( T) dependency corresponds to the ferromagnetic-paramagnetic phase tran sition occurring at the Curie temperature T(c) of the cobalt films, wh ich is also confirmed by experimental observation of the hysteresis be havior, Besides the measurement of Curie temperatures, the experimenta l technique presented here allows the determination of magnetic proper ties for ultrathin films even in the paramagnetic regime far above T(c ).