Evolution of electrical and magnetic properties with annealing treatments for GdCu films

Ultrafine Gd particles in a Cu metallic matrix have been obtained by post-annealing of as-sputtered metastable Gd_xCu_1-x alloys at temperatures higher than 250°C. The results of resistivity measurements show that the resistivities of as-sputtered metastable Gd_0.2Cu_0.8 and Gd_0.3Cu_0.7 alloys exhibit a resistivity minimum at low temperatures, an indication of the Kondo effect. In addition the temperature of the resistivity minimum rises with the increasing Gd content. Conversely, the resistivity of films after formation of Gd granules levels off at low temperatures. The magnetic results indicate that the metastable GdCu alloys are essentially a spin-glass at low temperature with the transition temperatures at around 3.5~5 K. However, magnetization data at 80 K shows that the as-sputtered samples contain some small Gd ferromagnetic clusters in the paramagnetic matrix. The magnetic particles of granular films begin to be thermally blocked at T _B and become magnetically ordered below T_B. Due to larger grain sizes, T_B is much higher for x=0.3 than for 0.2. The variation of transport and magnetic properties for samples with different annealing processes are described in detail