In this article, granular (NiFeCo)35Ag65 films having a nominal atomic ratio of Ni:Fe:Co=74:16:10, near the zero magnetostriction ternary alloy, were prepared by dc magnetron co-sputtering. Subsequent thermal annealing was performed in a vacuum (≪2×10-3 Pa) furnace for 1 h at various temperatures ranging from 250 to 500 °C. The crystalline structure and magnetic structure of the as-deposited and annealed films were characterized by Rutherford backscattering spectroscopy, x-ray diffraction, atomic force microscopy, and magnetic force microscopy. The giant magnetoresistance (GMR) for the films was measured as a function of temperature between 20 and 300 K using a conventional four-point probe dc technique in the presence of a magnetic field up to 7.6 kOe. It was found that, the crystalline structure, the magnetic structure, and consequently the GMR were closely related to the thermal treatment. The film annealed at the temperature of 300 °C has the isolated single domain structure and the highest GMR value of 19.1% at 20 K, while the film annealed at 500 °C has the long-range domain structure and the lowest GMR value of 9.9% at 20 K. © 2000 American Institute of Physics.