Simultaneous Individual and Dipolar Collective Properties in Binary Assemblies of Magnetic Nanoparticles
Journal article, 2020
Applications based on aggregates of magnetic nanoparticles are becoming increasingly widespread, ranging from hyperthermia to magnetic recording. However, although some uses require collective behavior, others need a more individual-like response, the conditions leading to either of these behaviors are still poorly understood. Here, we use nanoscale-uniform binary random dense mixtures with different proportions of oxide magnetic nanoparticles with low/high anisotropy as a valuable tool to explore the crossover from individual to collective behavior. Two different anisotropy scenarios have been studied in two series of binary compacts: M1, comprising maghemite (gamma-Fe2O3) nanoparticles of different sizes (9.0 nm/11.5 nm) with barely a factor of 2 between their anisotropy energies, and M2, mixing equally sized pure maghemite (low-anisotropy) and Co-doped maghemite (high-anisotropy) nanoparticles with a large difference in anisotropy energy (ratio > 8). Interestingly, while the M1 series exhibits collective behavior typical of strongly coupled dipolar systems, the M2 series presents a more complex scenario where different magnetic properties resemble either "individual-like" or "collective", crucially emphasizing that the collective character must be ascribed to specific properties and not to the system as a whole. The strong differences between the two series offer new insight (systematically ratified by simulations) into the subtle interplay between dipolar interactions, local anisotropy and sample heterogeneity to determine the behavior of dense assemblies of magnetic nanoparticles.
DYNAMICS
MODEL
SUPERPARAMAGNETISM
SPIN DISORDER
NANOCRYSTAL SUPERLATTICES
COFE2O4
REMANENCE
MAGNETORESISTANCE
RANDOM ANISOTROPY
CHARGE-DISTRIBUTION
Author
Elena H. Sanchez
University of Castilla, La Mancha
Marianna Vasilakaki
Catalan Institute of Nanoscience and Nanotechnology (ICN2)
Su Seong Lee
Inst Bioengn & Nanotechnol
Peter S. Normile
University of Castilla, La Mancha
Giuseppe Muscas
Uppsala University
University of Cagliari
Massimiliano Murgia
University of Castilla, La Mancha
University of Cagliari
Mikael Andersson
Uppsala University
Chalmers, Chemistry and Chemical Engineering, Energy and Material
Gurvinder Singh
The University of Sydney
Roland Mathieu
Uppsala University
Per Nordblad
Uppsala University
Pier Carlo Ricci
University of Cagliari
Davide Peddis
University of Genoa
National Research Council of Italy (CNR)
Kalliopi N. Trohidou
Catalan Institute of Nanoscience and Nanotechnology (ICN2)
Josep Nogues
Catalan Institution for Research and Advanced Studies
Spanish National Research Council (CSIC)
Jose A. De Toro
University of Castilla, La Mancha
Chemistry of Materials
0897-4756 (ISSN) 1520-5002 (eISSN)
Vol. 32 3 969-981Subject Categories
Inorganic Chemistry
Physical Chemistry
Condensed Matter Physics
DOI
10.1021/acs.chemmater.9b03268