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 N-2 and O-2. 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 N-2 and CO2 gases from paramagnetic O-2 gas. While the uptake of N-2 and CO2 leads to an increase in T-C through ferrimagnetic behavior, the uptake of O-2 results in an O-2 pressure-dependent continuous phase change from a ferrimagnet to an antiferromagnet, eventually leading to a novel ferrimagnet with aligned O-2 spins following application of a magnetic field. This chameleonic material, the first with switchable magnetism that can discriminate between similarly sized N-2 and O-2 gases, provides wide scope for new gas-responsive porous magnets.