Positron annihilation spectroscopic studies of ferromagnetic methylammonium lead iodide perovskite

Point defects in methylammonium lead iodide (MAPbI₃) are believed to be the source of its room-temperature ferromagnetic behavior. The existence of room-temperature ferromagnetism observed through the hysteresis in the M-H (magnetization vs. magnetic field) curve proves that ferromagnetism is possible even at room temperature in the tetragonal phases of MAPbI₃ system. Employing positron annihilation spectroscopy, the presence of a significant amount of point defects in the ball-mill ground MAPbI₃ sample has been identified. Coincidence Doppler broadening spectroscopy identifies that the point defects are mostly iodine vacancy (V˙_I) in MAPbI₃. Experimental data supports the theoretical prediction of iodine vacancy (V˙_I)-induced ferromagnetism in the cubic phase which exists at a little higher temperature than the room-temperature tetragonal phase for MAPbI₃. Moreover, the ab-initio band structure calculation shows the n-/p-type semiconducting behavior due to the vacancy formation in MAPbI₃. Ferromagnetism along with semiconducting properties makes it viable for spintronics applications.