Seminaria

Kondo-like behaviour and GMR effect in granular Co-Cu microwires

Granular materials consisting of small grains distributed inside a non-magnetic matrix exhibiting giant magnetoresistance (GMR) effect have attracted considerable attention since beginning of 1990-th. One of the common methods for obtaining such granular materials is a melt spinning technique involving rapid quenching from the melt. Glass-coated microwires prepared by so-called Taylor-Ulitovski technique involving rapid quenching from the melt present reduced dimensions (metallic nucleus diameters 1 - 30 um) and amorphous or metastable structure. Recently we reported on preparation of microwires with granular structure exhibiting considerable GMR effect). We prepared Cu_100-xCo_x (x=5,10,20) glass-coated microwires using Taylor-Ulitovsky technique and studied the influence of annealing on structure and temperature and magnetic field dependence of resistance. We measured temperature dependence of resistance, R(T), in as-prepared and annealed at 400 ^oC Cu₈₀Co₂₀, Cu₉₀Co₁₀ and Co₅Cu₉₅ microwires. We observed that Cu₉₅Co₅, Cu₈₀Co₂₀ and Cu₉₀Co₁₀ microwires present resistivity minimum at certain temperature, T_m. This minimum is very well defined for as-cast samples. T_m-values decreases after annealing (from about 50 K to about 25 K). Observed R(T) dependences and the minimum are well affected by applied magnetic field. Additionally we observed a significant increasing of the GMR effect in the samples annealed at high temperature (400 °C) with longer annealing time (up to 34% GMR effect). We found that the structure of CuCo microwires as well as the GMR effect is greatly affected by annealing. Considerable enhancement of the GMR effect related with structural changes of the studied samples is promising for technical applications.