Static and dynamic magnetic properties of spherical magnetite nanoparticles
- 1 September 2003
- journal article
- Published by AIP Publishing in Journal of Applied Physics
- Vol. 94 (5), 3520-3528
- https://doi.org/10.1063/1.1599959
Abstract
We present a detailed study of static and dynamic magnetic behavior of nanoparticles with average particle sizes 〈d〉 ranging from 5 to 150 nm. Bulk-like properties such as saturation magnetization, hyperfine parameters, coercive field, and Verwey transition are observed in 150 nm particles. For decreasing particle size, the Verwey temperature, shifts down to ∼20 K for and is no longer observable for smaller particles. The smallest particles display superparamagnetic behavior at room temperature, with transition to a blocked state at which depends on the applied field. The existence of surface spin disorder can be inferred from the decrease of saturation magnetization at low temperatures, as the average particle size is reduced. This disordered surface did not show effects of exchange coupling to the particle core, as observed from hysteresis loops after field cooling in a 7 T magnetic field. For particles with dynamic ac susceptibility measurements show a thermally activated Arrhenius–Néel dependence of the blocking temperature with applied frequency. The interparticle interactions are found to influence the energy barriers yielding an enhancement of the estimated magnetic anisotropy. From the calculus of the magnetic anisotropy, it is inferred that there is no structural transition from cubic to triclinic symmetry for in agreement with the absence of the Verwey transition. A value is obtained for the magnetocrystalline anisotropy constant of the cubic phase.
Keywords
This publication has 51 references indexed in Scilit:
- Magnetic dynamics of single-domain Ni nanoparticlesJournal of Applied Physics, 2003
- T2law for magnetite-based ferrofluidsJournal of Physics: Condensed Matter, 2003
- Magnetic dynamics of Zn/sup 57/Fe/sub 2/O/sub 4/ nanoparticles dispersed in a ZnO matrixIEEE Transactions on Magnetics, 2002
- Magnetic Relaxation of Interacting Co Clusters: Crossover from Two- to Three-Dimensional LatticesPhysical Review Letters, 2002
- Formation of cobalt nanoparticle dispersions in the presence of polysiloxane block copolymersPolymer, 2002
- Window and mixing effects in the dynamics of an LN2Raman laserJournal of Physics D: Applied Physics, 2002
- Anomalous moment and anisotropy behavior infilmsPhysical Review B, 1996
- Temperature dependence of spontaneous magnetization of ultrafine Fe particles in Fe-SiO2 granular solidsJournal of Applied Physics, 1987
- Rare-earth-rich metallic glasses. I. Magnetic hysteresisPhysical Review B, 1981
- Hysteresis in CuMn : The effect of spin orbit scattering on the anisotropy in the spin glass stateJournal de Physique, 1980