Gas-responsive porous magnet distinguishes the electron spin of molecular oxygen

Gas-sensing materials are becoming increasingly important in our society, requiring high sensitivity to differentiate similar gases like N₂ and O₂. For the design of such materials, the driving force of electronic host-guest interaction or host-framework changes during the sorption process has commonly been considered necessary; however, this work demonstrates the use of the magnetic characteristics intrinsic to the guest molecules for distinguishing between diamagnetic N₂ and CO₂ gases from paramagnetic O₂ gas. While the uptake of N₂ and CO₂ leads to an increase in T_C through ferrimagnetic behavior, the uptake of O₂ results in an O₂ pressure-dependent continuous phase change from a ferrimagnet to an antiferromagnet, eventually leading to a novel ferrimagnet with aligned O₂ spins following application of a magnetic field. This chameleonic material, the first with switchable magnetism that can discriminate between similarly sized N₂ and O₂ gases, provides wide scope for new gas-responsive porous magnets.