Gigantic Photomagnetic Effect at Room Temperature in Spiropyran-Protected FePt Nanoparticles

A key issue in molecular electronics is the control of electronic states and properties by optical stimuli, which enables fast and high-density data storage. In this article, we report preparation of a photoswitchable room-temperature ferromagnetic material using FePt nanoparticles protected with a photochromic spiropyran ligand. Magnetic properties were examined with a field-dependent isothermal magnetization, and a photomagnetic effect was measured at room temperature. These measurements revealed room-temperature ferromagnetism and reversible switching of magnetization by 60% upon photochromic reaction of the spiropyran ligand. This gigantic photomagnetic effect is explained as spiropyran's large change in the dipole moment during photochromic reaction that tunes the magnitude of electron transfer at the interface.