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.

Figure 1

XRD patterns of (a) N, (b) F, (c) FN and (d) NF NPs.

Figure 2

FTIR spectra of N, F, NF and FN NPs.

Figure 3

FESEM Images of (a) F, (b) N, (c) FN and (d) NF NPs.

Figure 4

HRTEM image and particle size distribution of (a) N, (b) F, (c) NF and (d) FN NPs.

Figure 5

SAED pattern and lattice fringes of (a) N, (b) F, (c) NF and (d) FN NPs.

Figure 6

(a,b) Elemental analysis of CS nanostructures (a) FN and (b) NF.

Figure 7

M-H loop for (a) N, (b) F, (c) NF and (d) FN NPs.

Figure 8

Variation of H_eb for CS FN and NF nanostructure with temperature.

Figure 9

Temperature dependence of M_r/M_s and H_c for CS (a) FN and (b) NF compared with single F phase NPs.

Figure 10

A schematic representation of negative and positive exchange bias of CS FiM-AFM and AFM-FiM NPs with spin configuration at two different temperatures of T_N ˂ T ˂ T_C and T ˂ T_N.

Figure 11

In-vitro cytotoxicity assay of FN sample incubated for 1 and 3 days using MG-63 cells.

Figure 12

Temperature versus time curves for (a) N, (b) F, (c) NF and (d) FN NPs at field amplitude H = 9.24 kAm⁻¹ and frequency f = 337 kHz.