Magnetization and magnetoresistance in melt-spun Cu80Fe5Ni15

Magnetization and magnetoresistance (MR) were studied (0 < H < 70 kOe, 4.2 K < T < 300 K) in as-cast and annealed (T-an = 400, 450, and 500 degreesC) samples of melt-spun Cu80Fe5Ni15. Field-cooled magnetization curves, when c ompared with the Curie-Weiss law, suggest the presence of antiferromagnetic interactions (Theta = -57 K) between nanoparticles for T-an = 450 and 500 degreesC. Antiferromagnetic interactions have been predicted when dipolar i nteractions dominate Ruderman-Kittel-Kasuya-Yosida interactions in large pa rticles. Here antiferromagnetic interactions are attributed to particles ro ughly 4 to 5 nm in size. The largest MR value (MR similar to 17% at H = 70 kOe and T = 10 K) is found for the as-cast material. For samples annealed a t 400 degreesC, MR curves are linear in H above 10 kOe and are in qualitati ve agreement with a model which considers short-range magnetic scattering b y particles of different sizes. (C) 2001 American Institute of Physics.