Tuning Exchange Bias in Core/Shell FeO/Fe₃O₄ Nanoparticles

Abstract

Monodisperse 35 nm FeO nanoparticles (NPs) were synthesized and oxidized in a dry air atmosphere into core/shell FeO/Fe(3)O(4) NPs with both FeO core and Fe(3)O(4) shell dimensions controlled by reaction temperature and time. Temperature-dependent magnetic properties were studied on FeO/Fe(3)O(4) NPs obtained from the FeO NPs oxidized at 60 and 100 °C for 30 min. A large exchange bias (shift in the hysteresis loop) was observed in these core/shell NPs. The relative dimensions of the core and shell determine not only the coercivity and exchange field but also the dominant reversal mechanism of the ferrimagnetic Fe(3)O(4) component. This is the first time demonstration of tuning exchange bias and of controlling asymmetric magnetization reversal in FeO/Fe(3)O(4) NPs with antiferromagnetic core and ferrimagnetic shell.

Engineered inorganic core/shell nanoparticles

“…A supplementary anisotropy terms is evidenced in metallic oxide core/shell nanostructures involving contacts between a ferro-or ferrimagnetic materials and an antiferromagnetic materials. It is due to exchange coupling between the spins at the interface between the ferromagnetic (FM) and antiferromagnetic (AFM) materials, called exchange bias [148,149,150,151,152,153,154,155]. The study of FM-AFM exchange interactions proposed interesting development to improve the performance of permanent magnetic materials by means of an enhancement of the coercivity deviation (n=5).…”

Spin dynamics and criteria for onset of exchange bias in superspin glass Fe/γ-Fe2O3core-shell nanoparticles

“…Recent experiments have also demonstrated EB in the case of samples having a FM layer in contact with a spin glass layer 12,13 ; layered nanoparticle/ferromagnetic structures where various models have been suggested to explain the origin of EB 14 . Core-shell nanoparticles with a conventional FM (core)/AFM (shell) and more recently "inverted" AFM (core)/FM (shell) have also been studied and the general consensus to explain EB is the freezing of interfacial spins or the growth of droplets with uncompensated spins [15][16][17] .…”

Well-controlled exchange bias effect in MnO@Mn3O4 core-shell nanoparticles with an inverted coupling structures

“…Progresses in chemical synthesis make it possible to controllable synthesis of inverted core-shell structures. 1 Sun et al 12 had synthesized the inverted core-shell FeO/Fe 3 O 4 nanocubes and studied the temperature effect on the tuning of exchange bias. MnO@Mn 3 O 4 core-shell NPs prepared by arc evaporating metallic Mn in air show very large coercivity (almost three-times that of bulk Mn 3 O 4 ) and unconventional exchange bias.…”