Magnetic ordering through itinerant ferromagnetism in a metal–organic framework

Materials that combine magnetic order with other desirable physical attributes could find transformative applications in spintronics, quantum sensing, low-density magnets and gas separations. Among potential multifunctional magnetic materials, metal–organic frameworks, in particular, bear structures that offer intrinsic porosity, vast chemical and structural programmability, and the tunability of electronic properties. Nevertheless, magnetic order within metal–organic frameworks has generally been limited to low temperatures, owing largely to challenges in creating a strong magnetic exchange. Here we employ the phenomenon of itinerant ferromagnetism to realize magnetic ordering at T C = 225 K in a mixed-valence chromium( ii/iii) triazolate compound, which represents the highest ferromagnetic ordering temperature yet observed in a metal–organic framework. The itinerant ferromagnetism proceeds through a double-exchange mechanism, which results in a barrierless charge transport below the Curie temperature and a large negative magnetoresistance of 23% at 5 K. These observations suggest applications for double-exchange-based coordination solids in the emergent fields of magnetoelectrics and spintronics. The development of metal–organic magnets that combine tunable magnetic properties with other desirable physical properties remains challenging despite numerous potential applications. Now, a mixed-valent chromium–triazolate material has been prepared that exhibits itinerant ferromagnetism with a magnetic ordering temperature of 225 K, a high conductivity and large negative magnetoresistance (23%).