Nanoscale Magnetism Control via Surface and Exchange Anisotropy for Optimized Ferrimagnetic Hysteresis

Abstract

With the aim of controlling nanoscale magnetism, we demonstrate an approach encompassing concepts of surface and exchange anisotropy while reflecting size, shape, and structural hybridization of nanoparticles. We visualize that cube has higher magnetization value than sphere with highest coercivity at 60 nm. Its hybridization into core-shell (CS) structure brings about a 14-fold increase in the coercivity with an exceptional energy conversion of magnetic field into thermal energy of 10600 W/g, the largest reported to date. Such capability of the CS-cube is highly effective for drug resistant cancer cell treatment.

Long‐Term Stability and Reproducibility of Magnetic Colloids Are Key Issues for Steady Values of Specific Power Absorption over Time

“…Indeed, MNPs synthesis through organic routes such as thermal decomposition of organic precursors, have reported size distributions among the narrowest values (σ<10%), [9] [10] [20] [21] whereas co-precipitation strategies based on the hydrolysis of a stoichiometric mixture of Fe 2+ and Fe 3+ ions to form Fe3O4 NPs usually result in broader distributions (σ>10%). [22] [23] [24] Also, reverse micelle synthesis has been reported to give average particle sizes within 2.92 < <d> < 8.95 nm (i.e., 0.061< σ/<d> <0.12) [25] Besides Gen et al prepared α-FeOOH nanorods at room temperature by a micoremulsion approach whose size were 8.2 ± 1.5 nm (σ/<d>=0.18) in diameter and 106 ± 16 nm (σ/<d>=6.62)in length.…”

“…Although there are synthetic routes capable to produce nearly single-size MNPs, [9] these protocols have not shown a similar precision on reproducibility of a given <d> value from batch to batch.…”

“…[30] [44] [45] Maximum values of SPA has been reported for Fe3O4 particles to be around 20-30 nm, [9,46] and therefore colloidal stability is difficult to obtain because not only aggregation but also precipitation processes. For the PEI-coated MNPs of this work, colloidal stability is provided by the polymer, which also defines the electrostatic and steric repulsion between MNPs.…”

“…[9], [10] Since power absorption depends critically on particle volume, these chemical routes provide good samples for testing the current SPA models.…”

Octapod iron oxide nanoparticles as high-performance T2 contrast agents for magnetic resonance imaging

“…The M s values of Octapod-30, Octapod-20, Spherical-16 and Spherical-10 were about 71, 51, 67 and 55 emu g À 1 , respectively. The slightly higher M s value of Octapod-30 than that of Spherical-16 may be due to the reduced spin canting effect in octapod morphology comparing with spherical particle 35 . Despite of similar M s values, the shape anisotropy in these octapod magnetite nanostructures and significantly increased effective radii of the magnetic cores may be responsible for the distinctly high T 2 relaxivities.…”