J.G. Santos

Magnetic resonance study of zero-field-frozen magnetite-based biocompatible magnetic fluid

In this paper, a biocompatible MF sample was investigated using X-band MR. The resonance linewidth broadening (/spl Delta/H/sub R/) and the resonance field (H/sub R/) was investigated as a function of temperature (T), at different nonparticle concentration. The biocompatible MF sample used in this study is based on magnetic nanoparticle (9.4 nm is average diameter) coated with dextran. After precipitation in alkaline medium, magnetite nanoparticles were surface coated to produce stable biocompatible MF samples at physiological pH and salinity.

Superexchange coupling on oleylsarcosine-coated magnetite nanoparticles

Room temperature ferromagnetic resonance was used to investigate particle-particle interaction in magnetic fluid samples containing magnetite nanoparticles surface coated with dimercaptosuccinic acid (DMSA) or oleylsarcosine (OLEL). The DMSA sample showed a decrease of the magnetic resonance field (MRF) increasing the nanoparticle concentration (phi), whereas the OLEL sample showed the opposite behavior. The DMSA MRF concentration dependence was explained using a dipolar interaction model beyond the point dipole approximation. In addition, the magnetic resonance spectra of the OLEL sample showed an optical mode suggesting an antiferromagnetic superexchange coupling between magnetic nanoparticles forming dimers.

Dynamic susceptibility investigation of biocompatible magnetic fluids: The surface coating effect

In this study room-temperature dynamic susceptibility measurements were used to investigate magnetite nanoparticles surface-coated with dextran and dimercaptosuccinic acid, both dispersed as biocompatible magnetic fluids. Multicomponent susceptibility curves were associated with the presence of monomers and dimers in the sample. Transmission electron microscopy data have been used to support the analysis carried out with the susceptibility data. The field dependence of the peak position of the imaginary component of the dynamical susceptibility was analyzed within the picture of an asymmetric double-well potential for the relaxation of the magnetic moment associated with the magnetite nanoparticle. The nanoparticle size dependence of the susceptibility peak position was taken into account in the data analysis. Nanoparticle-size parameters obtained from the analysis of the susceptibility data of the two samples (3.7 and 6.1nm) are in very good agreement with the values obtained from the fitting of the elec...

Dynamic susceptibility investigation of magnetite-based biocompatible magnetic fluids

In this study, dynamic susceptibility was used to investigate magnetite nanoparticles surface-coated with dextran and dimercaptosuccinic acid and dispersed as biocompatible magnetic fluids. Transmission electron microscopy data have been used to support the analysis carried out with the susceptibility data. The field dependence of the peak position of the imaginary component of the dynamical susceptibility was analyzed within the picture of an asymmetric double well potential for the relaxation of the magnetic moment associated to the magnetite nanoparticle. The size-dependence of the magnetic susceptibility was taken into account in the data analysis. Nanoparticle-size parameters obtained from the analysis of the susceptibility data of the two samples (3.7 and 6.1 nm) are in very good agreement with the values obtained from the fitting of the electron microscopy data (3.1 and 5.6 nm).