Large magnetoresistance observed in facing-target sputtered Ni-doped CN x amorphous composite films

Abstract

A series of amorphous Ni-doped CN x films with ∼23 at.% Ni were fabricated using facing-target sputtering at different nitrogen partial pressures ( P N). The films were composed of ∼1–4 nm Ni-rich particles embedded in a CN x matrix and turn from ferromagnetic at low temperatures to superparamagnetic at room temperature. The largest negative magnetoresistance ( MR = [ R( H) − R(0)]/ R(0)) reaches −59% at a P N of 4% and a temperature of 3 K. With a decrease of P N from 4% to 0%, the electrical transport mechanism changes from tunneling to variable-range hopping and the maximum MR drops from ∼59% to ∼3.8%. The MR– H curves show a weak saturation trend in a high-field regime and the MR– T curves follow the relation of log| MR| ∝ − T below 20 K for all the films, despite the difference in transport mechanism. The origin of the large MR (−59%) can be ascribed to a spin-related high-order tunneling process.