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

SILVANA J. STEWART; ALEJANDRA F. CABRERA; NICOLÁS A. FELLENZ; ROBERTO C. MERCADER; JOSÉ F. BENGOA; SERGIO G. MARCHETTI

JOURNAL OF PHYSICAL CHEMISTRY C

AMER CHEMICAL SOC

Lugar: Washington; Año: 2016

1932-7447

This is a study on the magnetism of a Fe2O3@MCM-41 composite madeup of iron (III) oxide nanocrystals of average length size of 4 nm embedded in thechannels of a MCM-41 mesoporous matrix. Through Mössbauer spectroscopy, x-rayabsorption experiments and static and dynamic magnetic measurements we identify theguest iron oxide entities as composed by exchange-coupled hematite (weakferromagnetic WF) and maghemite (ferrimagnetic FiM) arranged in a string of beadsconfiguration. The WF/FiM nanocrystals behave as independent particle moments thatblock as a whole (core and shell) below TB = 17 K. The lognormal energy barrierdistribution function determined from relaxation measurements shows a maximum at anenergy E=200 K. We also explore to which extent the contact between domains of thetwo coexisting oxides controls the magnetism of this bi-phasic nanosystem.