Photoinduced molecular switching studied by polarized neutron diffraction

The photo-induced magnetization density of the photoswitchable [Fe(ptz)₆](BF₄)₂ (ptz=1-propyltetra-zole) spin crossover compound is reported. The photoswitching process is observed by using a experimental setup allowing both light illumination and polarized neutron diffraction measurements (PND). We studied the photoexcitation kinetics, and the photoinduced magnetic properties of the [Fe(ptz)₆](BF₄)₂ compound by PND, which evidenced a complete photoprocess. The temperature dependence of the photoinduced magnetization obtained by PND is well described by an Ising model taking into account the magnetic anisotropy and the spin-orbit coupling. The thermal relaxation towards the stable electronic state was observed in the 55 60-K temperature interval. The magnetization density around the Fe position is well described by the Fe²⁺ magnetic form factor.