Field Dependence of Magnetic Disorder in Nanoparticles

Abstract

The performance characteristics of magnetic nanoparticles towards application, e.g. in medicine, imaging, or as sensors, is directly determined by their magnetization relaxation and total magnetic moment. In the commonly assumed picture, nanoparticles have a constant overall magnetic moment originating from the magnetization of the single-domain particle core surrounded by a surface region hosting spin disorder. In contrast, this work demonstrates the significant increase of the magnetic moment of ferrite nanoparticles with applied magnetic field. At low magnetic field, the homogeneously magnetized particle core initially coincides in size with the structurally coherent grain of 12.8(2) nm diameter, indicating a strong coupling between magnetic and structural disorder. Applied magnetic fields gradually polarize the uncorrelated, disordered surface spins, resulting in a magnetic volume more than 20\% larger than the structurally coherent core. The intraparticle magnetic disorder energy increases sharply towards the defect-rich surface as established by the field-dependence of the magnetization distribution. In consequence, these findings illustrate how the nanoparticle magnetization overcomes structural surface disorder. This new concept of intraparticle magnetization is deployable to other magnetic nanoparticle systems, where the in-depth knowledge of spin disorder and associated magnetic anisotropies will be decisive for a rational nanomaterials design.

arXiv comment40 pages, 14 figures, extensively revised (including change of title, appendix added)

References in corpus (12)

• Skyrmion Lattice in a Chiral Magnet
• Magnetic Charge Transport
• Phase instability induced by polar nanoregions in a relaxor ferroelectric system
• Surface contribution to the anisotropy of magnetic nanoparticles
• Enhancement of the magnetic anisotropy of nanometer-sized Co clusters: influence of the surface and of the inter-particle interactions
• Effective anisotropies and energy barriers of magnetic nanoparticles with Neel surface anisotropy
• Evidence for charge localization in the ferromagnetic phase of La_(1-x)Ca_(x)MnO_3 from High real-space-resolution x-ray diffraction
• Validity of the Néel-Arrhenius model for highly anisotropic Co_xFe_{3-x}O_4 nanoparticles
• Unusual enhancement of effective magnetic anisotropy with decreasing particle size in maghemite nanoparticles
• Size-dependent spatial magnetization profile of manganese-zinc ferrite Mn0.2Zn0.2Fe2.6O4 nanoparticles
• Surface spin canting in Fe3O4 and CoFe2O4 nanoparticles probed by high resolution electron energy loss spectroscopy
• Vacancy-driven non-cubic local structure and magnetic anisotropy tailoring in Fe${}_x$O-Fe${}_{3-\delta }$O${}_4$ nanocrystals

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• Micromagnetic simulation of neutron scattering from spherical nanoparticles: Effect of pore-type defects
• The benefits of a Bayesian analysis for the characterization of magnetic nanoparticles
• Neutron study of magnetic correlations in rare-earth-free Mn-Bi magnets
• Small-angle neutron scattering signatures of magnetic hopfions