Spin relaxation of localized electrons in monolayer MoSe₂: importance of random effective magnetic fields

We study the Hanle and spin polarization recovery effects on resident electrons in a monolayer MoSe₂ 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 MoSe₂ 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 non-zero in-plane g-factor |gₓ|≈ 0.1, the value of which is comparable to its dispersion, is attributed to randomly localized electrons in the MoSe₂ layer.