Magnetic and relaxometric properties of Mn ferrites

We present the magnetic properties and the 1H nuclear magnetic resonance dispersion profiles Mn-ferrites-based compounds, as possible novel contrast agents (CAs) for magnetic imaging (MRI). The samples consist of nanoparticles (NPs) with the magnetic core of Mn(1+x)Fe(2−x)O4, obtained by the rapid decomposition of metalcarbonyl into a hot containing an oxidizer and a coordinating surfactant; by this procedure, monodisperse NPs with different sizes have been obtained. We have performed structural and investigation by x-ray powder diffraction and transmission electron microscopy and SQUID magnetometry experiments to investigate the magnetic behaviour of samples. As required for MRI applications using negative CAs, the samples are at room temperature, having blocking temperatures in the range 14–80 K. longitudinal r1 and transverse r2 nuclear relaxivities appear to vary strongly with the core size, their values being comparable to commercial compounds in the-frequency range ν > 100 MHz. The experimental results suggest that our samples are for high-frequency MRI imagers in general and in particular for the 3 T clinical, as indeed suggested by a recent report (Tromsdorf et al 2007 Nanoletters 7 2422).