Particle size-dependent magnetic hyperthermia in gadolinium silicide micro- and nano-particles from calorimetry and AC magnetometry*

Self-regulating magnetic hyperthermia, in which heating of magnetic particles is limited by the magnetic transition temperature, could be a valuable form of magnetic hyperthermia for cancer treatment, as it can ensure uniform heating across tumor tissue. Gadolinium silicide has been suggested as a candidate material for self-regulating magnetic hyperthermia because of its high magnetization, Curie temperature (T_C) near the desired treatment temperature, and tunability. This work presents measurements of size-separated ball-milled Gd₅Si₄ particles, showing that the magnetization and specific loss power both decrease with decreasing particle size. Dynamic hysteresis loop measurements show that the coercivity of the particles is increased under the conditions used for magnetic hyperthermia (224 kHz, particles dispersed in water) relative to quasistatic measurements of powder samples. However, no particle size-dependence of the coercivity was observed. This work highlights one of the challenges of implementing self-regulating magnetic hyperthermia: materials tend to have low coercivity near T_C. Given this challenge, rare-earth compounds with high magnetization may provide the best opportunity to obtain significant heating for self-regulating hyperthermia.