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Superspin glass originating from dipolar interaction with controlled interparticle distance among γ-Fe 2 O 3 nanoparticles with silica shells

K. Hiroi,K. Komatsu,Tetsuya Sato

Published 2011 in Physical Review B

ABSTRACT

\ensuremath{\gamma}-Fe${}_{2}$O${}_{3}$/SiO${}_{2}$ core-shell nanoparticles with different shell thicknesses were prepared to elucidate the condition for superspin-glass (SSG) dynamics. As the shell thickness decreases, the contribution of interparticle dipolar interaction becomes apparent in the magnetic dynamics of nanoparticle assembly. The frequency dependence of peaks in ac-magnetic susceptibility in samples with strong interactions slows down, which is characterized as the emergence of a spin-glasslike phase. Aging in magnetization relaxation is found in a strongly interacting sample with an interparticle distance of $L\ensuremath{\leqslant}14$ nm but is scarce in a sample with $L$ $=$ 18 nm. Scaling analysis reveals an increase in superparamagnetic properties with an increase in $L$. Therefore the critical interparticle distance necessary for SSG transition is 15\char21{}18 nm with 11-nm $\ensuremath{\gamma}$-Fe${}_{2}$O${}_{3}$ nanoparticles. This corresponds to the ratio of interparticle-interaction energy to the magnetic-anisotropy energy ${E}_{\mathrm{dip}}$/${E}_{\mathrm{a}}$ of 6\char21{}12%.

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