Magnetic Properties and Losses of Iron/Cobalt-Based Ferrofluids Kent Hess, W. Korzi, L. Krushinski, K. Langford, O. Thomas, M. Devadas, E. Hondrogiannis, V. Smolyaninova

Ferrofluids have fascinating properties not only for basic research, but also because of
their potential in medical and optical applications. Ferrofluids are composed of
magnetic nanoparticles that are suspended in carrier fluid. When placed into a
magnetic field, ferrofluids form chains of nanoparticles along the direction of the magnetic field. Iron/Cobalt-based (FeCo) ferrofluids and FeCo ferrofluids with gold where synthesized and characterised. FeCo nanoparticles have large magnetic moments as well as sufficient conductivity. Magnetization of ferrofluids and nanoparticles were measured with VSM. Particle size distribution was determined with SEM. Magnetization curves were used to estimate the thickness of magnetically inactive layer. When ferrofluid is placed in ac magnetic field, the magnetic moment of the nanoparticles changes direction rapidly, which leads to dissipation of energy (losses) through heating. Losses were measured in ac magnetic field at different frequencies and compared with losses in iron oxide-based ferrofluids. Significant losses in FeCo-based ferrofluids and higher frequencies can lead to the potential medical applications of these ferrofluids such as hyperthermia cancer treatment.