Approaching the physical limits of specific absorption rate for synthetic antiferromagnetic nanodisks in hyperthermia applications

Abstract

Magnetic nanoparticle-based hyperthermia presents a promising approach to treating malignant solid tumors that are resistant to conventional therapies such as chemotherapy and radiation. However, the therapeutic potential of superparamagnetic iron oxide nanoparticles (SPIONs) is limited by low saturation magnetization, superparamagnetic behavior, and broad particle size distribution. Here, we present synthetic antiferromagnetic disk particles (SAF-MDPs) designed through micromagnetic modeling to maximize hysteretic heating while maintaining suspension stability. The SAF-MDPs feature in-plane magnetization optimized via uniaxial anisotropy adjustments to prevent spin-flop phenomena and eliminate hysteresis-free loops along the hard axis. Mechanofluidic modeling was used to assess particle alignment under an alternating magnetic field (AMF), and advanced magnetic characterization, including in-vacuum single-particle magnetic force microscopy, was employed to elucidate the switching process between antiferromagnetic and ferromagnetic states. The resulting SAF-MDPs approach the theoretical maximum specific loss power (SLP) allowed under the biological discomfort level, yielding significantly higher heating efficiency than SPIONs. This combined modeling–fabrication–characterization strategy opens a pathway toward magnetic hyperthermia agents operating near fundamental performance limits, with potential for further optimization through material choice and coupling-engineering strategies.