Spin relaxation of localized electrons in monolayer MoSe 2 : Importance of random effective magnetic fields

We study the Hanle and spin polarization recovery effects on resident electrons in a monolayer ${\mathrm{MoSe}}₂$ on EuS. We demonstrate that localized electrons provide the main contribution to the spin dynamics signal at low temperatures below 15 K for small magnetic fields of only a few mT. The spin relaxation of these electrons is determined by random effective magnetic fields due to a contact spin interaction, namely the hyperfine interaction with the nuclei in ${\mathrm{MoSe}}₂$ or the exchange interaction with the magnetic ions of the EuS film. From the magnetic field angular dependence of the spin polarization we evaluate the anisotropy of the intervalley electron $g$ factor and the spin relaxation time. The nonzero in-plane $g$ factor $|{g}_x|\ensuremath{\approx}0.1$, the value of which is comparable to its dispersion, is attributed to randomly localized electrons in the ${\mathrm{MoSe}}₂$ layer.