I am developing an alternating magnetic field (AMF) device to induce hyperthermia in SPION of ~20nm size. The SPION is based on Fe3O4 (magnetite?) Many papers demonstrated that AMF of 80--150KHz is effective for heating SPIONs of smaller than 35nm, in tissue. Many other works, particulaly theory-works, indicated that ~Mhz range should be more effective for particles smaller than 20nm. Is there any expert out there who could give me some suggestions for the AMF frequency needed to maximize the heating of ~20nm SPION in aquous solution? BTW, the field strength of my AMF is between 150--270 Gauss, and frequency 90--150KHz, and this AMF shows effectiveness in heating 1.5 micron size magnetic microspheres. Thanks a lot