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.

Effect of Fe/Fe3O4 Nanoparticles Stray Field on the Microwave Magnetoresistance of a CoFeB/Ta/CoFeB Synthetic Ferrimagnet

“…Micromagnetic modeling of the spin-valve films under the NP stray fields shows a complicated structure with various types of magnetization reversal . Additional factors such as demagnetization of the NPs themselves, easy-axis rotation of the NPs, and a nonmagnetic gap between the NPs and ferromagnetic platform were revealed and experimentally observed. , Nevertheless, most of the experimental data are related to the current–voltage characteristics of a spin valve covered by NPs. − A deeper understanding of these results was obtained by analyzing the local magnetization and resistance of a spin valve covered by NPs.…”

Self‐Assembly of Nanoparticles into Two‐Dimensional Arrays for Catalytic Applications

“…The NP 2D arrays prepared via the interfacial assembly method show many potential applications, including the creation of ferrimagnetic CoFe 2 O 4 NP arrays for magnetic recording (Figure a) and spin‐valves, as well as the fabrication of Au NP monolayers for flexible flash memories (Figure b) and surface enhanced Raman scattering ,. In the remainder of this review we focus on recent studies using 2D NP arrays as catalysts for some important chemical reactions, including those for energy conversion and fuel formation.…”

Controlled Spreading Rates to Distribute Nanoparticles as Uniform Langmuir Films

“…Langmuir–Blodgett (LB) and Langmuir–Schaefer (LS) methods have been used to deposit Langmuir films of NPs onto solid surfaces. − The NPs are dispersed in a nonpolar organic solvent such as chloroform or toluene, and the liquid dispersion is deposited as a Langmuir film onto a polar subphase such as water. The solvent spreads on the surface of the subphase, carrying the NPs with it.…”

“…As the solvent evaporates, the NPs assemble on the surface to form a Langmuir film. Structures and patterns for NPs in the Langmuir films have been characterized by combinations of Brewster angle microscopy (BAM) or microfluorescence imaging ,,,,− and grazing angle X-ray scattering. ,, Microstructures formed in transferred LB/LS films of NPs are widely reported from images obtained using transmission electron microscopy (TEM) or scanning electron microscopy (SEM). ,,,,,− ,, The most common close-packed arrangement resembles a two-dimensional (2-D) hexagonal lattice with varying degrees of rotational disorders or random local displacements of NPs in the unit cells.…”

“…38,49,50 Microstructures formed in transferred LB/LS films of NPs are widely reported from images obtained using transmission electron microscopy (TEM) or scanning electron microscopy (SEM). 16,30,32,34,35,[37][38][39][40][41]43,44 The most common close-packed arrangement resembles a two-dimensional (2-D) hexagonal lattice with varying degrees of rotational disorders or random local displacements of NPs in the unit cells.…”