Magnetoresistances of ultrathin fine Cu-particle and CuAu-particle films

We have measured the magnetoresistances in approximate to 30-Angstrom-thick fine Cu-particle and Au-doped Cu-particle (CuAu-particle) films between 2.1 and 4.2 K and in magnetic fields H up to 6 T, with sheet resistances R(square)(4.2 K) of the films ranging from approximate to 10 k Omega to 2 M Omega. We find that the magnetoresistances are positive, exhibiting broad maxima, at low H, while they can change sign and become negative at high H. The magnitudes of the normalized magnetoresistances, Delta R(square)(H)/R(square)(0) = [R(square)(H) - R(square)(0)]/R(square)(0), are of the order of a tenth of a percent, depending on the values of R(square). Particularly, the magnetoresistances in pure Cu-particle films are essentially isotropic, regardless of the orientation of H being applied parallel or perpendicular to the film plane. In CuAu-particle films, however, more negative perpendicular magnetoresistances relative to parallel magnetoresistances are observed. There observations are closely connected with the fine-particle structure of our films. Explanation for our experimental results in terms of current theories is presented.