Crossover From Individual to Collective Magnetism in Dense Nanoparticle Systems: Local Anisotropy Versus Dipolar Interactions
Journal article, 2022
Dense systems of magnetic nanoparticles may exhibit dipolar collective behavior. However, two fundamental questions remain unsolved: i) whether the transition temperature may be affected by the particle anisotropy or it is essentially determined by the intensity of the interparticle dipolar interactions, and ii) what is the minimum ratio of dipole–dipole interaction (Edd) to nanoparticle anisotropy (KefV, anisotropy⋅volume) energies necessary to crossover from individual to collective behavior. A series of particle assemblies with similarly intense dipolar interactions but widely varying anisotropy is studied. The Kef is tuned through different degrees of cobalt-doping in maghemite nanoparticles, resulting in a variation of nearly an order of magnitude. All the bare particle compacts display collective behavior, except the one made with the highest anisotropy particles, which presents “marginal” features. Thus, a threshold of KefV/Edd ≈ 130 to suppress collective behavior is derived, in good agreement with Monte Carlo simulations. This translates into a crossover value of ≈1.7 for the easily accessible parameter TMAX(interacting)/TMAX(non-interacting) (ratio of the peak temperatures of the zero-field-cooled magnetization curves of interacting and dilute particle systems), which is successfully tested against the literature to predict the individual-like/collective behavior of any given interacting particle assembly comprising relatively uniform particles.
magnetic anisotropy
dipolar interactions
superspin glass
magnetic nanoparticles
Author
Elena H. Sánchez
University of Castilla, La Mancha
Marianna Vasilakaki
National Center for Scientific Research “Demokritos”
Su Seong Lee
Agency for Science, Technology and Research (A*STAR)
Peter S. Normile
University of Castilla, La Mancha
Michael Andersson-Sarning
Chalmers, Chemistry and Chemical Engineering, Chemical Technology
Uppsala University
R. Mathieu
Uppsala University
Alberto López-Ortega
Universidad Publica de Navarra
University of Castilla, La Mancha
Benoit P. Pichon
Institut Universitaire de France
University of Strasbourg
Davide Peddis
Consiglo Nazionale Delle Richerche
University of Genoa
Chris Binns
University of Castilla, La Mancha
P. Nordblad
Uppsala University
Kalliopi Trohidou
National Center for Scientific Research “Demokritos”
Josep Nogués
Institut Catala de Nanociencia i Nanotecnologia
Catalan Institution for Research and Advanced Studies
José A. De Toro
University of Castilla, La Mancha
Small
1613-6810 (ISSN) 1613-6829 (eISSN)
Vol. 18 28 2106762Subject Categories
Physical Chemistry
Materials Chemistry
Condensed Matter Physics
DOI
10.1002/smll.202106762
PubMed
35689307