Inhomogeneity effects on magnetic and magnetotransport properties of CoxCu100−x films produced by ultrashort pulsed laser deposition

Abstract

Films produced by means of ultrashort pulsed laser deposition (uPLD) and constituted of Co nanoparticles (NPs) mixed with Cu ones exhibit peculiar morphological and topological properties. In particular, the NPs obtained by uPLD retain their individuality with a moderate coalescence which permits interparticle discontinuities. Due to this condition, the NP interface contributes significantly to the electron transport mechanisms depending on the magnetizing field. As a consequence, magnetoresistance effects are evidenced which do not saturate up to external magnetizing fields much higher than the value required for the saturation of the macroscopic magnetization. Moreover, when the cobalt volume fraction (x) is lower than 35%, the set of magnetic, resistive and magnetoresistive data shows that the magnetic percolation among the Co particles is not completely obtained and a transport mechanism of the giant magnetoresistance (GMR) kind is active in the uPLD films, notwithstanding the fact that the average particle size is higher in comparison with that expected for GMR optimization. On the other hand, if the contact among Co particles is obtained (x ⩾ 50%) the anisotropic magnetoresistance (AMR) becomes the prominent effect. In this circumstance, the presence of interparticle discontinuities is still deducible by the experimental evidence of a negative derivative of the magnetoresistance ratio versus the applied magnetic field. In the same x range (x ⩾ 50%), the AMR increases with the Co content, while zero field resistivity does not change.