Experimental evidence of exchange forces between nanoparticles in a superparamagnetic system

• Published in: Journal of physics. D, Applied physics Vol. 55; no. 36; pp. 365002 - 365010
• Main Authors: de Araújo, João Carlos Rocha, de Moraes Iglesias, Carlos Augusto, da Silva, Rodolfo Bezerra, Araujo Barbosa, Suzana, Xavier, Jayson, Silva Filho, Ernani Dias da, Cardozo Fonseca, José Luis, Souza, Paloma Boeck, Campos Plá Cid, Cristiani, Machado, Fernando Luis de Araujo, da Silva, Edimilson Félix, Gamino, Matheus, de Medeiros, Suzana Nóbrega, Correa, Marcio Assolin, Bohn, Felipe
• Format: Journal Article
• Language: English
• Published: IOP Publishing 08.09.2022
• Subjects: exchange forces; magnetic interactions; nanoparticles; superparamagnetism
• ISSN: 0022-3727; 1361-6463
• DOI: 10.1088/1361-6463/ac7268

Abstract Although interacting superparamagnetic systems have been widely explored, in most cases the correlations are only assigned to dipolar interactions. Here, we perform a systematic investigation of the properties of superparamagnetic MgFe 2 O 4 nanoparticles, a system with characteristics that led us to believe they are associated with the existence of exchange interactions in the system. We first confirm that our sample consists of pure MgFe 2 O 4 nanoparticles, having an average size of ∼12 nm and superparamagnetic behavior at room temperature with an irreversibility temperature of 250 K. Nevertheless, we reveal that the magnetic response is not well described by the Langevin function, even when taking into account the size distribution of the nanoparticles. In order to address the reasons for such deviation from the non-interacting behavior of a superparamagnetic system, we focus our attention on equilibrium and dynamic magnetization measurements, and consider a theoretical approach in the context of mean-field approximation, in which the effects of interactions in the sample are investigated. From the results, we find a positive value of 243 K for the parameter Θ associated with the mean field. Such a condition imposes the existence of magnetizing effects due to interactions in the system, which, according to Weiss’ mean field theory, are a fingerprint of the presence of exchange forces between nanoparticles.