Abstract
Induction heating, a contactless and efficient method for generating heat via alternating magnetic fields (AMFs), has evolved from simple thermal applications to precise process control in fields like catalysis, self-healing, and debonding. Magnetic nanoparticles (NPs) play a key role as heat mediators, with heating properties adjustable via composition, size, and interactions. However, spatially precise heat control remains challenging. Current strategies rely on external AMF adjustments or material modifications, but lack an inherent mechanism to predefine which particles or regions will be activated for induction heating, limiting applicability in structured materials or complex environments. Here, it is shown that pre-magnetizing cobalt-doped iron oxide NPs with a static magnetic field irreversibly enhances their heating rates by up to a factor of 40. This process permanently alters their magnetic properties, enabling selective heating independent of AMF modulation. The extent of activation scales with cobalt content, introducing a material-intrinsic thermal switch. Furthermore, assembling these NPs into supraparticles facilitates integration into functional materials. By enabling spatially resolved and selective heat generation, this strategy advances the control of induction heating at the material level. It opens new possibilities for on-demand, pre-programmable, spatially resolved thermal activation in composite materials, smart adhesives, and targeted energy delivery in complex systems.