Magnetic interactions based on proton orbital motion in CH₃NH₃PbI₃ and CH₃NH₃PbBr₃

The microscopic origin of the remarkable optoelectronic properties of one of the most studied contemporary materials remains unclear. Here, we identify the existence of magnetic interactions between intermolecular proton orbitals in CH₃NH₃PbI₃ and CH₃NH₃PbBr₃. In particular, a unique sharp drop and a pronounced step-up discontinuity in the magnetic susceptibility at the tetragonal-to-cubic phase transitions are identified in CH₃NH₃PbI₃ and CH₃NH₃PbBr₃, respectively. The magnetic interactions in the orthorhombic and tetragonal phases are dependent on thermal history and lattice orientation while nearly independent of the applied external magnetic field. In CH₃NH₃PbBr₃, the CH₃ and NH₃⁺ components reorient in an uncorrelated fashion resulting the cubic phase to also exhibit magnetic anisotropy. Our findings provide a potential link connecting the highly light-absorbing CH₃NH₃⁺ and the exceptional properties of the charge carriers of the inorganic framework in hybrid perovskite solar cells.