CoFe₂O₄ nanoparticle-integrated spin-valve thin films prepared by interfacial self-assembly

Abstract

We report the fabrication of nanoparticle-integrated spin-valve system and investigate its magnetic properties and magnetotransport behaviors. Using a modified interfacial self-assembly method, chemically synthesized CoFe₂O₄ nanoparticles were assembled as a Langmuir film on liquid/air interface. This film was further deposited on the sputtered thin films of bottom-pinned spin valve without additional treatment. The nanoparticle-assembled film with multilayer structure exhibits uniform and compact surfaces. Magnetization and magnetoresistance study show that the integrated nanoparticles give rise to a reduced interlayer coupling field and an increased magnetoresistance (MR) ratio in the spin valve. By analyzing the magnetic interaction between the nanoparticles and the spin valve, it is inferred that the magnetic stray field induced by the single-domain magnetic nanoparticles reduces the external magnetic field on the free layer, leading to the change of free-layer magnetization and the attenuation of interlayer coupling. The decrease of this ferromagnetic-type interlayer coupling resulted in a more favorable antiparallel magnetization configuration, manifested by the enhancement of MR ratio. This work demonstrates the integration of self-assembled nanoparticles with exchange-biased thin films, and the results suggest that nanoparticle integration can be employed as an alternative route to modulate the magnetization switching and magnetoresistance of spin valves.