TY - JOUR
T1 - Evolution of morphology and magnetic properties in silica/maghemite nanocomposites
AU - Li, Dan
AU - Teoh, Wey Yang
AU - Woodward, Robert C.
AU - Cashion, John D.
AU - Selomulya, Cordelia
AU - Amal, Rose
PY - 2009/7/16
Y1 - 2009/7/16
N2 - The morphological evolution of SiO2/γ-Fe2O 3 nanocomposites was systematically synthesized in a one-step flame spray pyrolysis. Under these conditions, a gradual transformation from discrete γ-Fe2O3 nanoparticles to thin SiO2 coatings, segregated single γ-Fe2O3 core, and multiple γ-Fe2O3 cores within a SiO2 matrix was obtained as a function of SiO2 loading. The presence of SiO 2 up to 13% has a pronounced effect on the j γ-Fe 2O3 crystallite structure (transforming from P4132 to Fd3m space group) and its cationic vacancy ordering.Decrease in the latter was further reflected through the intrinsic magnetic properties of the γ-Fe2O3 cores (i.e., decreasing specific saturation magnetization and increasing coercivity and exchange bias). Deviation from the magnon-type thermal dependence, T3/2 Bloch law, was observed for nanocomposites with SiO2 content above 13%. The Ms vs T curves could be fitted with the sum of an exponential component and a Bloch law component, where the magnitude of the exponential component increased with increasing SiO2 content above 13% SiO2. The thermal dependence of the saturation magnetization for these samples could not be adequately explained by a finite size effect or via freezing of canted spins. © 2009 American Chemical Society.
AB - The morphological evolution of SiO2/γ-Fe2O 3 nanocomposites was systematically synthesized in a one-step flame spray pyrolysis. Under these conditions, a gradual transformation from discrete γ-Fe2O3 nanoparticles to thin SiO2 coatings, segregated single γ-Fe2O3 core, and multiple γ-Fe2O3 cores within a SiO2 matrix was obtained as a function of SiO2 loading. The presence of SiO 2 up to 13% has a pronounced effect on the j γ-Fe 2O3 crystallite structure (transforming from P4132 to Fd3m space group) and its cationic vacancy ordering.Decrease in the latter was further reflected through the intrinsic magnetic properties of the γ-Fe2O3 cores (i.e., decreasing specific saturation magnetization and increasing coercivity and exchange bias). Deviation from the magnon-type thermal dependence, T3/2 Bloch law, was observed for nanocomposites with SiO2 content above 13%. The Ms vs T curves could be fitted with the sum of an exponential component and a Bloch law component, where the magnitude of the exponential component increased with increasing SiO2 content above 13% SiO2. The thermal dependence of the saturation magnetization for these samples could not be adequately explained by a finite size effect or via freezing of canted spins. © 2009 American Chemical Society.
UR - http://www.scopus.com/inward/record.url?scp=68149131499&partnerID=8YFLogxK
UR - https://www.scopus.com/record/pubmetrics.uri?eid=2-s2.0-68149131499&origin=recordpage
U2 - 10.1021/jp902684g
DO - 10.1021/jp902684g
M3 - RGC 21 - Publication in refereed journal
SN - 1932-7447
VL - 113
SP - 12040
EP - 12047
JO - The Journal of Physical Chemistry C
JF - The Journal of Physical Chemistry C
IS - 28
ER -