Magnetic resonance was used to investigate the kinetic disposition of magnetite nanoparticles (9.4 nm core diameter) from the blood circulation after intravenous injection of magnetite-based dextran-coated magnetic fluid in female Swiss mice. In the first 60 min the time-decay of the nanoparticle concentration in the blood circulation follows the one-exponential (one-compartment) model with a half-life of (6.9 +/- 0.7) min. The X-band spectra show a broad single line at g approximately 2, typical of nanomagnetic particles suspended in a nonmagnetic matrix. The resonance field shifts toward higher values as the particle concentration reduces, following two distinct regimes. At the higher concentration regime (above 10(14) cm(-3)) the particle-particle interaction responds for the nonlinear behavior, while at the lower concentration regime (below 10(14) cm(-3)) the particle-particle interaction is ruled out and the system recovers the linearity due to the demagnetizing field effect alone.
Angular measurements of magnetic resonance are used to investigate the surface anisotropy field as well as the exchange anisotropy field in spherical MnFe2O4 magnetic nanoparticles as a function of temperature and particle diameter (D). The resonance field is a combination of angular dependent and angular independent fields, both affected by the surface anisotropy field, which in turn follows a D−α power law, with α very close to unity. The angular dependent component probes the surface anisotropy field while the angular independent component probes the exchange anisotropy field. In the temperature range from 100 to 250 K a negative surface anisotropy field is found, which increases as the particle size is reduced, indicating a radial orientation of the spins at the MnFe2O4 nanoparticle surface.
In this work, CdS nanocrystals (NCs) doped with Mn were synthesized in a glass matrix by fusion. The as-grown Cd1−xMnxS NCs were investigated by optical absorption, atomic force microscopy, and electron paramagnetic resonance (EPR). The incorporation of Mn2+ ions in CdS NCs was confirmed by an absorption transition blueshift with increasing Mn concentration x. EPR spectra demonstrated the existence of two distinct Mn2+ ion locations: one incorporated in the core and the other near the surface of the Cd1−xMnxS NCs. The hyperfine interaction constants used to simulate the EPR spectra were A=7.6 and 8.2 mT, respectively. The synthesis of high quality Cd1−xMnxS NCs may allow the control of optical and magnetic properties.
Samples of Pb1−xMnxSe nanocrystals were synthesized by fusion method and characterized by optical absorption, atomic force microscopy, x-ray diffraction, and electron paramagnetic resonance (EPR) techniques. Effects of Mn2+ ion incorporation into PbSe nanocrystals are manifested by well resolved optical spectra for different concentrations of Mn. The EPR spectra of as grown and thermal annealed Pb1−xMnxSe samples show that the magnetic properties of these Mn-doped nanocrystals can be tuned by thermal processes using different annealing times.
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