Annealing dependence of giant magnetoresistance in CuFeNi alloys

Giant magnetoresistance (GMR) in granular CuFeNi alloys is comparable in magnitude to that observed in CuCo. Here we study magnetization M and GMR (0 < H < 70 kOe; 4.2 K < T < 300 K) in metal-spun and annealed Cu80Fe20-xNix (x = 0, 2.5, 5, 10, and 15) as a function of annealing temperature T-an < 500 degrees C, using a superconducting quantum interference device (SQUID) magnetometer. A wide variety of granular structures characterized by different average values of the particle sizes is obtained for different Fe/Ni ratios and annealing conditions. For Cu80Fe10Ni10, neither M nor GMR exhibit static hysteresis for T > 50 K. At this temperature, the largest GMR value (19%) was obtained for a sample annealed at 400 degrees C for 2 h. In Cu80Fe5Ni15, on the other hand, the microstructure and magnetic properties of the alloy are much more sensitive to annealing. The magnetoresistence is strongly dependent upon both the annealing and the measuring temperatures. For Fe-rich Cu80Fe20-xNix, the magnetic properties other alloys show a weak dependence upon annealing temperature. Magnetization curves for both as-cast and annealed alloys indicate many large particles which saturate at low magnetic fields. GMR versus alloy composition is presented for two annealing temperatures. (C) 2000 American Institute of Physics. [S0021-8979(00)57608-7].