Effect of Composition on the Spin Relaxation of Lead Halide Perovskites

Lead halide perovskites have been promising candidates in spintronics applications; however, the mechanism of spin relaxation is still unclear. Here, we compare the temperature-dependent spin dynamics of four perovskite films (XPbY3) with different compositions (X = CH3NH3, Cs; Y = I, Br). The room-temperature net spin lifetime is found to increase as the molar mass decreases, indicating the dominant role of spin orbital coupling in their spin relaxation. As the temperature is reduced from room temperature to 77 K, the spin relaxations in CH3NH3PbI3 and CsPbI3 are significantly slowed down while those of CH3NH3PbBr3 and CsPbBr3 are only slightly changed. Based on the analysis of phonon scattering of perovskites, it is suggested that two different mechanisms, Elliot-Yafet in which spin flips upon momentum scattering and D'yakonov-Perel in which spin relaxes between momentum scattering, are responsible for the spin relaxation in XPbI3 and XPbBr3 (X = CH3NH3, Cs), respectively.