Modulation of magnetoresistance and field sensitivity of Co–ZnO nanocomposite film by microstructure controlling

Recently, magnetic metal-semiconductor nanocomposite films with a uniform superparamagnetic structure have attracted increasing interest in negative magnetoresistance (MR) properties at room temperature (RT). In this work, we have designed and prepared an original nonuniform structure with coexistence of size-distributed ferromagnetic Co clusters and superparamagnetic Co particles in Co–ZnO nanocomposite films, with Co content between 41 and 65 at.%. The film with 49 at.% Co shows a large RT negative MR with a maximum value of over 9.5%. As Co content increasing, the ferromagnetic Co clusters grow both in quantity and size. Meanwhile, the curves of normalized MR become broader, and the peaks of the normalized MR field sensitivity (FS) shift to higher fields. It is noteworthy that the increase in ferromagnetic Co clusters can effectively modulate the MR FS, which is reasonably explained by establishing a mechanism model with the localized magnetization flux effect and inhomogeneous current paths based on size-distributed ferromagnetic Co clusters. This nonuniform structure can be extended to other nanocomposite materials for the modulation of MR FS by microstructure control in various application scenarios.