Remanence plots as a probe of spin disorder in magnetic nanoparticles
De Toro, José A. (Instituto Regional de Investigación Científica Aplicada)
Vasilakaki, Marianna (Ethniko Kentro Ereunas Physikōn Epistēmōn "Demokritos")
Lee, Su Seong (Institute of Bioengineering and Nanotechnology)
Andersson, Mikael S. (Uppsala University. Department of Engineering Sciences)
Normile, Peter S. (Instituto Regional de Investigación Científica Aplicada)
Yaacoub, Nader (Université du Maine. Institut des Molécules et Mateŕiaux du Mans)
Murray, Peyton D. (University of California. Physics Department)
Sánchez, Elena H. (Instituto Regional de Investigación Científica Aplicada)
Muñiz, Pablo (Instituto Regional de Investigación Científica Aplicada)
Peddis, Davide (Istituto di Struttura della Materia)
Mathieu, Roland (Uppsala University. Department of Engineering Sciences)
Liu, Kai (University of California. Physics Department)
Geshev, Julian (Universidade Federal Do Rio Grande Do sul. Instituto de Física)
Trohidou, Kalliopi N. (Ethniko Kentro Ereunas Physikōn Epistēmōn "Demokritos")
Nogués, Josep (Institut Català de Nanociència i Nanotecnologia)

Data:	2017
Resum:	Remanence magnetization plots (e. g. , Henkel or δM plots) have been extensively used as a straightforward way to determine the presence and intensity of dipolar and exchange interactions in assemblies of magnetic nanoparticles or single domain grains. Their evaluation is particularly important in functional materials whose performance is strongly affected by the intensity of interparticle interactions, such as patterned recording media and nanostructured permanent magnets, as well as in applications such as hyperthermia and magnetic resonance imaging. Here, we demonstrate that δM plots may be misleading when the nanoparticles do not have a homogeneous internal magnetic configuration. Substantial dips in the M plots of γ-FeO nanoparticles isolated by thick SiO shells indicate the presence of demagnetizing interactions, usually identified as dipolar interactions. Our results, however, demonstrate that it is the inhomogeneous spin structure of the nanoparticles, as most clearly evidenced by Mössbauer measurements, that has a pronounced effect on the δM plots, leading to features remarkably similar to those produced by dipolar interactions. X-ray diffraction results combined with magnetic characterization indicate that this inhomogeneity is due to the presence of surface structural (and spin) disorder. Monte Carlo simulations unambiguously corroborate the critical role of the internal magnetic structure in the δM plots. Our findings constitute a cautionary tale on the widespread use of remanence plots to assess interparticle interactions as well as offer new perspectives in the use of Henkel and δM plots to quantify the rather elusive inhomogeneous magnetization states in nanoparticles.
Ajuts:	Ministerio de Economía y Competitividad MAT2015-65295-R Ministerio de Economía y Competitividad MAT2016-77391-R Agència de Gestió d'Ajuts Universitaris i de Recerca 2014/SGR-1015 Ministerio de Economía y Competitividad SEV-2013-0295
Drets:	Tots els drets reservats.
Llengua:	Anglès
Document:	Article ; recerca ; Versió sotmesa a revisió
Matèria:	Cautionary tales ; Dipolar interaction ; Inhomogeneities ; Inter-particle interaction ; Magnetic characterization ; Magnetic configuration ; Magnetic nano-particles ; Recording media
Publicat a:	Chemistry of materials, Vol. 29, Issue 19 (October 2017) , p. 8258-8268, ISSN 1520-5002

DOI: 10.1021/acs.chemmater.7b02522

Preprint 39 p, 934.4 KB

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