Effect of nonuniform microstructure on magnetoresistance and field sensitivity in Co–MgO nanocomposite films.

Co–MgO metal-insulator nanocomposite films have attracted increasing interest for their high resistivity and negative magnetoresistance at room temperature. In this study, nonuniform-microstructure Co–MgO nanocomposite films were produced, in which superparamagnetic particles and ferromagnetic clusters coexist. At the Co content of 36 at.%, the film exhibits a high room-temperature negative magnetoresistance value of over 2.2%, and a high resistivity of 7.0 × 104 μΩ m. When Co content increases, the size and quantity of Co clusters gradually increase, which causes the peaks shifting of magnetoresistance field sensitivity to higher field. Moreover, we have established a mechanism mode to explain this phenomenon, by inducing the localized magnetization flux effect and inhomogeneous current paths effect. The high-resistivity nonuniform-microstructure Co–MgO nanocomposites are realized, which can be used in different application scenarios by modulating magnetoresistance field sensitivity. • Nonuniform Co–MgO nanocomposite films show the coexistence of ferromagnetic clusters and superparamagnetic particles. • The film with 36 at.% Co content shows a large RT negative MR of 2.2% and a high resistivity of 7 × 104 μΩ m. • Significant modulation of MR field sensitivity is obtained by microstructure controlling. [ABSTRACT FROM AUTHOR]