Nanocomposites consisting of nanoparticles of iron oxide (Fe3O4) and iron carbide (Fe3C) with a core-shell structure (Fe core, Fe3O4 and/or Fe3C shells) coated with additional graphite-like carbon layer dispersed in carbon matrix have been synthesized by solid-phase pyrolysis of iron-phthalocyanine (FePc) and iron-porphyrin (FePr) with a pyrolysis temperature of 900°C, and post-annealing conducted at temperatures ranging from 150°C to 550°C under controlled oxygen- and/or nitrogen-rich environments. A comprehensive analysis of the samples’ morphology, composition, structure, size, and magnetic characteristics was performed by utilizing scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-STEM) with elemental mapping, X-ray diffraction analysis (XRD), and magnetic measurements by utilizing vibrating sample magnetometry (VSM). The effect of the annealing process on magnetic performance and efficient control of the hysteresis loop and specific absorption rate (SAR) are discussed.
- Award ID(s):
- 2009358
- NSF-PAR ID:
- 10328924
- Date Published:
- Journal Name:
- Applied Sciences
- Volume:
- 11
- Issue:
- 14
- ISSN:
- 2076-3417
- Page Range / eLocation ID:
- 6637
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
We investigate the spatial distribution of spin orientation in magnetic nanoparticles consisting of hard and soft magnetic layers. The nanoparticles are synthesized in a core–shell spherical morphology where the target stoichiometry of the magnetically hard, high anisotropy layer is CoFe2O4 (CFO), while the synthesis protocol of the lower anisotropy material is known to produce Fe3O4. The nanoparticles have a mean diameter of ∼9.2–9.6 nm and are synthesized as two variants: a conventional hard/soft core–shell structure with a CFO core/FO shell (CFO@FO) and the inverted structure FO core/CFO shell (FO@CFO). High-resolution electron microscopy confirms the coherent spinel structure across the core–shell boundary in both variants, while magnetometry indicates the nanoparticles are superparamagnetic at 300 K and develop a considerable anisotropy at reduced temperatures. Low-temperature M vs H loops suggest a multistep reversal process. Small angle neutron scattering (SANS) with full polarization analysis reveals a considerable alignment of the spins perpendicular to the field even at fields approaching saturation. The perpendicular magnetization is surprisingly correlated from one nanoparticle to the next, though the interaction is of limited range. More significantly, the SANS data reveal a pronounced difference in the reversal process of the magnetization parallel to the field for the two nanoparticle variants. For the CFO@FO nanoparticles, the core and shell magnetizations appear to track each other through the coercive region, while in the FO@CFO variant, the softer Fe3O4 core reverses before the higher anisotropy CoFe2O4 shell, consistent with expectations from mesoscale magnetic modeling. These results highlight the interplay between interfacial exchange coupling and anisotropy as a means to tune the composite properties of the nanoparticles for tailored applications including biomedical/theranostic uses.more » « less
-
Abstract Magneto‐optical (MO) coupling incorporates photon‐induced change of magnetic polarization that can be adopted in ultrafast switching, optical isolators, mode convertors, and optical data storage components for advanced optical integrated circuits. However, integrating plasmonic, magnetic, and dielectric properties in one single material system poses challenges since one natural material can hardly possess all these functionalities. Here, co‐deposition of a three‐phase heterostructure composed of a durable conductive nitride matrix with embedded core–shell vertically aligned nanopillars, is demonstrated. The unique coupling between ferromagnetic NiO core and atomically sharp plasmonic Au shell enables strong MO activity out‐of‐plane at room temperature. Further, a template growth process is applied, which significantly enhances the ordering of the nanopillar array. The ordered nanostructure offers two schemes of spin polarization which result in stronger antisymmetry of Kerr rotation. The presented complex hybrid metamaterial platform with strong magnetic and optical anisotropies is promising for tunable and modulated all‐optical‐based nanodevices.
-
The ternary manganese pnictide phases, MnAs 1− x Sb x , are of interest for magnetic refrigeration and waste heat recovery due to their magnetocaloric properties, maximized at the Curie temperature ( T C ), which varies from 580–240 K, depending on composition. Nanoparticles potentially enable application in microelectronics (cooling) or graded composites that can operate over a wide temperature range, but manganese pnictides are synthetically challenging to realize as discrete nanoparticles and their fundamental magnetic properties have not been extensively studied. Accordingly, colloidal synthesis methods were employed to target discrete MnAs x Sb 1− x nanoparticles ( x = 0.1–0.9) by arrested precipitation reactions of Mn 2 (CO) 10 with (C 6 H 5 ) 3 AsO and (C 6 H 5 ) 3 Sb in coordinating solvents. The MnAs x Sb 1− x particles are spherical in morphology with average diameters 10–13 nm (standard deviations <20% based on transmission electron microscopy analysis). X-Ray fluorescence spectroscopy measurements on ensembles showed that all phases had an excess of Sb relative to the targeted composition, whereas energy dispersive spectroscopic mapping data of single particles revealed that the nanoparticles are inhomogeneous, adopting a core–shell structure, with the amorphous shell rich in Mn and O (and sometimes Sb) while the crystalline core is rich in Mn, As, and Sb. Magnetization measurements of the nanoparticle ensemble demonstrated the presence of both ferromagnetic and paramagnetic phases. By combining the magnetization measurements with precision chemical mapping and simple modeling, we were able to unambiguously attribute ferromagnetism to the MnAs x Sb 1− x crystalline core, whereas paramagnetism was attributed to the amorphous shell. Magnetization measurements at variable temperatures were used to determine the superparamagnetic transition of the nanoparticles, although for some compositions and particle sizes the blocking temperature exceeded room temperature. Preliminary magnetic studies also revealed a conventional dependence between core size and coercivity, in spite of variable compositions of the nanoparticles, an unexpected result.more » « less
-
null (Ed.)Gadolinium silicide (Gd 5 Si 4 ) nanoparticles are an interesting class of materials due to their high magnetization, low Curie temperature, low toxicity in biological environments and their multifunctional properties. We report the magnetic and magnetothermal properties of gadolinium silicide (Gd 5 Si 4 ) nanoparticles prepared by surfactant-assisted ball milling of arc melted bulk ingots of the compound. Using different milling times and speeds, a wide range of crystallite sizes (13–43 nm) could be produced and a reduction in Curie temperature ( T C ) from 340 K to 317 K was achieved, making these nanoparticles suitable for self-controlled magnetic hyperthermia applications. The magnetothermal effect was measured in applied AC magnetic fields of amplitude 164–239 Oe and frequencies 163–519 kHz. All particles showed magnetic heating with a strong dependence of the specific absorption rate (SAR) on the average crystallite size. The highest SAR of 3.7 W g −1 was measured for 43 nm sized nanoparticles of Gd 5 Si 4 . The high SAR and low T C , (within the therapeutic range for magnetothermal therapy) makes the Gd 5 Si 4 behave like self-regulating heat switches that would be suitable for self-controlled magnetic hyperthermia applications after biocompatibility and cytotoxicity tests.more » « less