Magnetic Relaxation of Gd-Doped MnFe2O4 Nanoparticles for MR Effect and Heat Dissipation

MnGdxFe2-xO4 nanoparticles ( ${x} =0$ , 0.05, 0.10) encapsulated in amorphous SiO2 were prepared by doping with a small amount of Gd ions, and their magnetic relaxation and magnetic resonance (MR) effects were investigated. The samples were prepared by wet mixing of metal chlorides and sodium metasilicate solutions, and the particle size was controlled to 18 nm by adjusting the annealing temperature. ${T} _{1}$ and ${T} _{2}$ relaxation measurements were performed by spin-echo method and MR signals were measured. All samples showed a shortening effect of ${T} _{2}$ relaxation. These phenomena would be attributed to the strong effect of the magnetic moment of Gd, which has a maximum of seven unpaired electrons in the $4{f}$ orbitals on the protons. A dominant shortening effect was also observed at ${T} _{1}$ signals. The same sample was examined to see if it would function as a reagent for hyperthermia treatment. Temperature rises in an ac magnetic field and in vitro experiments using human breast cancer cells were carried out. As a result, a superior hyperthermia effect was observed, and these samples are expected to be an agent with theranostic function in the future.