Bi-Magnetic Iron(III) Oxide Nanocrystals Embedded in MCM-41 Mesoporous Silica

N. A. FELLENZ; S. G. MARCHETTI; A. F. CABRERA; J. F. BENGOA; S. J. STEWART; R. C. MERCADER

JOURNAL OF PHYSICAL CHEMISTRY C

AMER CHEMICAL SOC

Lugar: Washington; Año: 2016 vol. 120 p. 2993 - 3000

1932-7447

This is a study on the magnetism of a Fe2O3@MCM-41composite made up of iron(III) oxide nanocrystals of average length sizeof 4 nm embedded in the channels of a MCM-41 mesoporous matrix.Through Mössbauer spectroscopy, X-ray absorption experiments andstatic and dynamic magnetic measurements, we identify the guest ironoxide entities as composed by exchange-coupled hematite (weakferromagnetic WF) and maghemite (ferrimagnetic FiM) arranged in astring of beads configuration. The WF/FiM nanocrystals behave asindependent particle moments that block as a whole below TB = 17 K.The log-normal energy barrier distribution function determined fromrelaxation measurements shows a maximum at an energy E= 200 K. Weexplore to what extent the contact between domains of the twocoexisting oxides controls the magnetism of this biphasic nanosystem.