Insights into the Structural and Microscopic Origin of Magnetic Properties of the γ-Fe₂O₃@Mn_xO_y Nanostructure

Abstract

Hetero-nanostructures having multi-layered ferromagnetic–antiferromagnetic ultrathin films, dispersion of ferromagnetic particles to the antiferromagnetic matrix, and a core–shell model (F@AF) can exhibit an exchange bias (H EB) that will be useful for spintronic materials such as spin valves, magnetic random-access memories, and ultrahigh data storage. The spin proximity effect of F and AF in the monodispersed core–shell is not much reported. For the first time, we report the preparation of core–shell monodispersed nanoparticles of γ-Fe2O3@Mn x O y having different thicknesses of shells. The microscopic origin of magnetic properties and the microscopic crystal structure are explained by experimental results such as energy-dispersive analysis of X-rays line scanning, X-ray absorption near-edge spectroscopy, and magnetic data. The values of H EB for γ-Fe2O3@Mn x O y (Mn6) and γ-Fe2O3@Mn x O y (Mn12) are found to be 8 and 79 Oe, respectively. Also, possible theoretical models such as crystal field stabilization energy for normal or inverse spinel structures and possible magnetic proximity interactions in core@shell models are discussed. Interestingly, samples show the heating behavior required for hyperthermia under an AC magnetic field, and materials will be potential for hyperthermia cancer therapy. Thermal decomposition of γ-Fe2O3@Mn x O y produces α-Fe2–2x Mn2x O3 at 550 °C, but their unit cell volumes are almost the same even after occupancy of 12 at. % Mn3+ in Fe3+ sites, and the origin of this behavior is explained for the first time.

Development of Core@Shell γ-Fe2O3@MnxOy@SiO2 Nanoparticles for Hyperthermia, Targeting, and Imaging Applications

“…C, core:γ-Fe 2 O 3 is named as IONP, whereas core@shell γ-Fe 2 O 3 @ Mn x O y particles (Mn atomic percentage with respect to Fe: 6 and 12) are named as IONP-Mn6 and IONP-Mn12, respectively. 22 Their corresponding silica coated nanoparticles are named IONP-SiO, IONP-Mn6-SiO, and IONP-Mn12-SiO, respectively, and further these particles are coated with PEG and their corresponding PEG coated nanoparticles are named IONP-SiO-PEG, IONP-Mn6-SiO-PEG, and IONP-Mn12-SiO-PEG, respectively. Further FA coated IONP-SiO, IONP-Mn6-SiO, and IONP-Mn12-SiO are named as IONP-SiO-FA, IONP-Mn6-SiO-FA, and IONP-Mn12-SiO-FA, respectively.…”

“…In our previous work, TEM images of IONP, IONP-Mn6, and IONP-Mn12 were provided. 22 The TEM image of IONP-Si is shown in Figure 2a. IONP is coated with silica.…”

“…19−21 In this line, we have published details of magnetic properties of core@shell nanoparticles (i.e., γ-Fe 2 O 3 @Mn x O y nanoparticles) and an exchange bias between the ferromagnetic core and the antiferromagnetic shell has been observed. 22 This is known as the proximity effects in magnetic terms. The exchange bias was found to increase with the increment of the thickness of the antiferromagnetic shell and decrement of ferromagnetic character.…”

Mesoporous NaGdF4/Ho–Yb@m-SiO2 Upconversion Nanophosphors as a Potent Theranostic Probe

“…The Fourier transform infrared (FTIR) spectra of UCNPs along with UCNPs@mSiO 2 are shown in Figure S3, and the peaks are assigned as per the reported ones. 19,20 2.3.1. Upconversion Nanoparticles.…”

“…While DOX-loaded UCNPs would have potential applications in cancer therapy as a chemotherapeutic formulation, [ 177 Lu]­Lu–NaGdF 4 /Ho–Yb@m-SiO 2 would be useful in nuclear medicine as a theranostic probe because suitable decay properties of 177 Lu are useful in SPECT imaging as well as therapy. Lutetium-177 is one of the most important radioisotopes extensively used in nuclear medicine for the management of cancer treatment. − In addition, β – emission (497 keV) with a maximum penetration tissue range of ∼2.5 mm from 177 Lu is useful for imaging, and concomitant emission of gamma photons of suitable energies (113 and 208 keV) enables simultaneous molecular imaging through SPECT. Figure shows the schematic diagram demonstrating the potential material of NaGdF 4 /Ho–Yb@m-SiO 2 UCNPs for multifunctional theranostic applications.…”