Magnetic properties of the MRI enhancement agent Feridex from Mössbauer spectra.

Mössbauer spectra of Feridex, an MRI enhancement agent, show that it contains superparamagnetic γ-Fe2O3 nanoparticles. From spectra in magnetic fields applied at room temperature the magnetic moment of the particles was measured to be 11,250 μB, from which the diameters of the single-domain particles are estimated to be about 8 nm. This is smaller than the hydrodynamic particle size of 30 nm which includes a protective coating of dextran. The particles are monodisperse, as shown by the continuous change from a broad superparamagnetic line to a magnetic 6-line pattern as the temperature is lowered below the blocking temperature TB of about 90 K. The magnetic moments and blocking temperature are consistent with those of γ-Fe2O3 samples of known sizes. [ABSTRACT FROM AUTHOR]