Title :
Magnetization Drop at High Temperature in Oleic Acid-Coated Magnetite Nanoparticles
Author :
Rodríguez, C. ; Bañobre-López, M. ; Kolen, Yu V. ; Rodríguez, B. ; Freitas, P. ; Rivas, J.
Author_Institution :
Int. Iberian Nanotechnol. Lab. (INL), Braga, Portugal
Abstract :
In this work we report an irreversible behavior in the magnetization of oleic acid (OA)-coated magnetite nanoparticles (NPs) at high temperature. On one hand, when the sample is heated-up, an irreversible magnetization drop is observed at 550 K, while the Curie temperature (Tc ≈ 840 K) remains close to that of bulk magnetite. On the other hand, a significant reduction of the magnetic moment has been found after heating and cooling the sample above and below its Curie temperature, respectively. Both magnetic features have been also observed in other surface modified magnetite nanoparticles [e.g., polyvynil pyrrolidone (PVP)-coated]. However, no reduction of the magnetic moment upon a heating-cooling cycle has been found in ligand-free magnetite nanoparticles. This fact suggests that surface effects derived from the OA-coating could be the origin of such reduction of the magnetic moment, as a consequence of thermal decomposition of the organic layer surrounding the nanoparticle and the subsequent loss of the magnetic surface order. This feature could be an important factor for those applications requiring high temperatures.
Keywords :
Curie temperature; iron compounds; magnetic moments; magnetic particles; magnetisation; nanomagnetics; nanoparticles; organic compounds; pyrolysis; surface magnetism; Curie temperature; Fe3O4; cooling; heating; ligand-free magnetite nanoparticles; magnetic moment; magnetic property; magnetic surface order; magnetization; oleic acid-coated magnetite nanoparticles; organic layer; polyvynil pyrrolidone; temperature 550 K; thermal decomposition; Heating; Magnetic moments; Magnetic resonance imaging; Magnetic separation; Nanoparticles; Saturation magnetization; Surface treatment; Magnetite nanoparticles; surface functionalization; surface spin disorder;
Journal_Title :
Magnetics, IEEE Transactions on
DOI :
10.1109/TMAG.2012.2194273