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

Abstract

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 near the desired treatment temperature, and tunability. Previous measurements of polydisperse micro- and nano-particles prepared from ball-milled Gd5Si4 yielded a decreased Curie temperature TC with a broad transition, suggesting that particle size may be used to tune TC. Other studies of size-selected particles of ball-milled Gd5Si4 showed decreased TC and magnetization with decreased particle size, but increased coercivity with decreased size, and the combined effects on the specific loss power were unknown. This work presents measurements of the particle size-dependence of the specific loss power of ball-milled Gd5Si4, showing that the largest particles (approx. 780 nm) behave similarly to the previously measured polydisperse samples, while the smaller particles all have decreased specific loss power. Dynamic hysteresis loop measurements show that the coercivity of the particles is increased under the conditions used for magnetic hyperthermia (particles dispersed in water, under an alternating magnetic field) relative to quasistatic measurements of powder samples, though a particle size-dependence of the coercivity was not observed under hyperthermia conditions. This work highlights one of the challenges of implementing self-regulating magnetic hyperthermia: in general, materials tend to have low coercivity near the magnetic transition temperature. Given this challenge, rare-earth compounds with high magnetization may provide the best opportunity to obtain significant heating for self-regulating hyperthermia.