PHYS 97 |
| Time-dependent magnetization induced by the optical spin-flip excitations in chemically synthesized superparamagnetic transition metal oxides (maghemite, magnetite and cobalt ferrite) nanocrystals were investigated. The dynamics of demagnetization and its recovery upon excitation of the spin-forbidden ligand field transition were measured via time-resolved Faraday rotation. Immediately after the photo excitation, the reduced ionic magnetic moments and the frustration of the magnetic ordering among the magnetic moments resulted in the ultrafast demagnetization. The recovery of the magnetization occurred on two different time scales. The amplitude of the magnetization recovery showed a strong dependence on the nanocrystal size, which reflects the size-dependent ferrimagnetic ordering throughout the volume of the nanocrystals. The effect of doping of Co ion in the host structure of magnetite, which also modifies the ferrimagnetic ordering, was also examined. |
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Nanostructured Materials
8:20 AM-12:00 PM, Monday, April 7, 2008 Morial Convention Center -- Rm. 338/339, Oral
Division of Physical Chemistry |