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Influence of Hard/Soft Layer Ordering on Magnetization Reversal of Bimagnetic Nanoparticles: Implications for Biomedical/Theranostic Applications



Corisa Kons, Kathryn L. Krycka, Joshua Robles, Nikolaos Ntallis, Manuel Pereiro, Manh-Huong Phan, Hariharan Srikanth, Julie A. Borchers, Dario A. Arena


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 magnetically hard, high anisotropy layer is CoFe2O4 (CFO) while the lower anisotropy material is Fe3O4 (FO). 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 multi-step reversal process. Small angle neutron scattering (SANS) with full polarization analysis reveals a considerable alignment of the spins perpendicular to the field even in 1.56 T. 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 micromagnetics modeling. These results highlight the interplay between interfacial exchange coupling and anisotropy as a means to tune the composite properties of the nanoparticles.
ACS Applied Nano Materials


Polarized SANS, Core/Shell Nanoparticles, Exchange Coupling, Magnetization Revesal


Kons, C. , Krycka, K. , Robles, J. , Ntallis, N. , Pereiro, M. , Phan, M. , Srikanth, H. , Borchers, J. and Arena, D. (2023), Influence of Hard/Soft Layer Ordering on Magnetization Reversal of Bimagnetic Nanoparticles: Implications for Biomedical/Theranostic Applications, ACS Applied Nano Materials, [online], (Accessed June 15, 2024)


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Created June 14, 2023, Updated January 23, 2024