Influence of spin dynamics of defects on weak localization in paramagnetic 2D metals

Spin-flip scattering of charge carriers in metals with magnetic defects leads to the low-temperature saturation of the decoherence time, $\tau_\varphi$, of electrons at the value comparable to their spin relaxation time, $\tau_s$. In two-dimensional (2D) conductors such a saturation can be lifted by an in-plane magnetic field, $B_\parallel$, which polarizes spins of scatterers without affecting orbital motion of free carriers. Here, we show that in 2D conductors with substantially different values of the g-factors of electrons ($g_e$) and magnetic defects ($g_i$), the decoherence time $\tau_\varphi(B_\parallel)$ (reflected by the curvature of magnetoconductance) displays an anomaly: it first gets shorter, decaying on the scale $B_\parallel\sim \hbar/|g_i-g_e|\mu_B \tau_s$, before becoming longer at higher values of $B_\parallel$.