DETERMINATION OF PARAMAGNETIC AND FERROMAGNETIC COMPONENTS OF MAGNETIZATION AND MAGNETORESISTANCE OF GRANULAR CO/AG FILMS

Several series of thin films (approximately 3000 angstrom) were fabricated by coevaporation of Co and Ag in a dual e-beam UHV system at substrate temperatures, T(S), between 300 and 500 K. The composition was varied between 23 and 54 at. % Co. The maximum measured magnetoresistance was 31% at room and 67% at nitrogen temperature. Magnetization and Rutherford backscattering measurements showed that the Co and Ag atoms are completely segregated for films deposited at T(c) greater-than-or-equal-to 400 K. The magnetoresistance (MR) and magnetization curves have been analyzed taking into account both the paramagnetic (PM) and ferromagnetic (FM) contributions that are observed to be present. The films having less-than-or-equal-to 32 at. % Co are entirely paramagnetic. The fraction of Co atoms in the ferromagnetic component increases monotonically with increasing T(S) and/or at. % Co. The average radii of the PM granules in the films having an MR effect of 25%-31% are approximately 20-22 angstrom with a minimum average separation of approximately 10 A. The large MR values attained in both the PM and FM components are attributed to the small effective domain sizes, approximately 40-50 angstrom. The MR values are large because the MR effect varies inversely as the mean-free-path for magnetic boundary scattering which is the average distance between domain boundaries. The variation of the resistive and magnetic behavior of the films was also studied as a function of the annealing time for an annealing temperature of 300-degrees-C. A striking behavior seen in these films is the long relaxation times when a FM component is present.