A comparative investigation of normal and inverted exchange bias effect for magnetic fluid hyperthermia applications

Abstract

Exchange bias (EB) of magnetic nanoparticles (MNPs) in the nanoscale regime has been extensively studied by researchers, which have opened up a novel approach in tuning the magnetic anisotropy properties of magnetic nanoparticles (MNPs) in prospective application of biomedical research such as magnetic hyperthermia. In this work, we report a comparative study on the effect of magnetic EB of normal and inverted core@shell (CS) nanostructures and its influence on the heating efficiency by synthesizing Antiferromagnetic (AFM) NiO (N) and Ferrimagnetic (FiM) Fe3O4 (F). The formation of CS structures for both systems is clearly authenticated by XRD and HRTEM analyses. The magnetic properties were extensively studied by Vibrating Sample Magnetometer (VSM). We reported that the inverted CS NiO@Fe3O4 (NF) MNPs have shown a greater EB owing to higher uncompensated spins at the interface of the AFM, in comparison to the normal CS Fe3O4@NiO (FN) MNPs. Both the CS systems have shown higher SAR values in comparison to the single-phased F owing to the EB coupling at the interface. However, the higher surface anisotropy of F shell with more EB field for NF enhanced the SAR value as compared to FN system. The EB coupling is hindered at higher concentrations of NF MNPs because of the enhanced dipolar interactions (agglomeration of nanoparticles). Both the CS systems reach to the hyperthermia temperature within 10 min. The cyto-compatibility analysis resulted in the excellent cell viability (> 75%) for 3 days in the presence of the synthesized NPs upto 1 mg/ml. These observations endorsed the suitability of CS nanoassemblies for magnetic fluid hyperthermia applications.

Tailoring Interfacial Exchange Anisotropy in Hard–Soft Core-Shell Ferrite Nanoparticles for Magnetic Hyperthermia Applications

“…Several research groups reported SAR of various compositions and geometry-dependent nanoparticles to explore the interface effect for magnetic heating [24][25][26]. Magnetic coupling across the interface of the different magnetic phases provides the NPs with exchange bias (EB) properties that helps in the efficient conversion of electromagnetic energy into heat for magnetic hyperthermia [27]. However, the effect of the core-shell geometry on the magnetic anisotropy and magnetization dynamics such as Neel and Brownian relaxations is not clearly understood.…”

A temperature-dependent switching of the exchange bias effect from negative to positive under a fixed intermediate cooling field

“…As shown in the gure, a strong FiM-AFM interface coupling is evident for CS FO@N displaying a larger harness as both the coercivity and squareness ratio are much higher compared to those of a single bare FO sample. 10,24 The EB eld (H EB ) and coercivity (H C ) of samples were extracted from the hysteresis loop of magnetization using formulas:…”

“…As shown in the figure, a strong FiM–AFM interface coupling is evident for CS FO@N displaying a larger harness as both the coercivity and squareness ratio are much higher compared to those of a single bare FO sample. 10,24 The EB field ( H EB ) and coercivity ( H C ) of samples were extracted from the hysteresis loop of magnetization using formulas: H EB = ( H C1 + H C2 )/2 and H C = ( H C1 − H C2 )/2, where H C1 and H C2 represent the coercive fields of the left and right branches of M–H loops along with their sign, respectively. The switching of EBE from negative to positive for the NP system was first reported by Ihab et al for the FiM–FiM CS nanostructure.…”

“…The horizontal shiing of the M-H loop appears to be negative or positive depending on the interface coupling proximity, temperature, and applied cooling eld. [10][11][12] Meiklejohn et al in 1956 rst reported the novel existence of EBE or negative EBE in the oxidized surface of Co particles. 2 Aer four decades (1966), Nogues et al discovered the rst kind of positive EBE in Fe/ MnF 2 and Fe/FeFe 2 bilayer systems.…”

Nanoparticles for Magnetic Heating: When Two (or More) Is Better Than One

“…Tsopoe et al carried out a comparative study on the exchange bias effect in antiferromagnetic/ferrimagnetic CS_NPs, with structure NiO/Fe 3 O 4 and Fe 3 O 4 /NiO [ 100 ]. These structures were also synthesized in two steps: first the precipitation in water of the NiO or Fe 3 O 4 core; then the precipitation of the other salt in the presence of the core and sodium acetate in ethylene glycol, in an autoclave at 180 °C for 10 h. CS_NPs between 30–35 nm showed colloidal stability thanks to the polyol rests at the surface.…”