In the realm of magnetic nanoparticles, a new study has unveiled insights that could significantly impact the energy sector, particularly in the field of magnetic hyperthermia therapy and beyond. Researchers, led by Elizabeth M. Jefremovas from the University of Luxembourg, have mapped the magnetization of iron-oxide nanoflowers, connecting their microstructure to their macroscopic magnetic response. This work, published in ‘Small Science’ (which translates to ‘Small Science’ in English), offers a fresh perspective on how spin disorder influences the behavior of these nanoparticles, potentially paving the way for more efficient nanoheaters.
Iron-oxide nanoflowers (NFs) have long been recognized for their efficiency as nanoheaters in magnetic hyperthermia therapy, a treatment that uses magnetic nanoparticles to heat and destroy cancer cells. However, the underlying physics governing the dynamic response of these nanoparticles, especially those beyond the single-domain limit and containing disorder, has remained poorly understood. Jefremovas and her team addressed this gap using large-scale micromagnetic simulations to map the magnetization of biocompatible iron-oxide NFs ranging from 10 to 400 nanometers in diameter.
The study revealed that above the single-domain regime (d > 50 nm), the magnetization of these nanoflowers folds into a vortex state. Within this state, the coercivity—the resistance of a magnetic material to becoming demagnetized—reaches a secondary maximum, a phenomenon not observed in nondisordered nanoparticles. This finding is significant because it highlights how disorder within the nanoparticles can tune their magnetic properties.
“The dynamics of the vortex shows two distinct reversal modes,” explained Jefremovas. “One is core-dominated, with an increasing coercivity with size, and the other is flux-closure-domains dominated, with a decreasing coercivity-size dependence.” The coercivity maximum is located at the transition between these two reversal modes, resulting from the combination of grain anisotropy and grain-boundary pinning.
This research provides the first detailed description of spin textures in iron oxide NFs beyond the macrospin framework. It reveals how particles with identical static magnetization can exhibit fundamentally distinct dynamics, leading to different macroscopic behaviors. By adjusting the grain size, the coercivity “sweet spot” can be tailored, offering a practical route to next-generation, high-efficiency nanoheaters.
The implications of this research extend beyond medical applications. In the energy sector, understanding and controlling the magnetic properties of nanoparticles can lead to more efficient energy storage and conversion technologies. For instance, the ability to tailor the coercivity of magnetic materials can improve the performance of devices such as transformers, motors, and generators, which are crucial for renewable energy systems.
Moreover, the insights gained from this study could inspire new approaches to designing magnetic materials for various applications, from data storage to sensing technologies. As Jefremovas noted, “This work opens up new avenues for exploring the potential of magnetic nanoparticles in diverse fields, not just in medicine but also in energy and beyond.”
In summary, the research led by Elizabeth M. Jefremovas and her team at the University of Luxembourg represents a significant step forward in understanding the magnetic behavior of iron-oxide nanoflowers. By elucidating the role of spin disorder and vortex dynamics, this study offers a roadmap for developing more efficient and tailored magnetic materials, with profound implications for the energy sector and other industries. As published in ‘Small Science’, this work underscores the importance of fundamental research in driving technological innovation and shaping the future of energy technologies.