Role of atomic spin-mechanical coupling in the problem of magnetic biocompass

It is a well established notion that animals can detect the Earth's magnetic field, while the biophysical origin of such magnetoreception is still elusive. Recently, a magnetic receptor Drosophila CG8198 (MagR) with a rod-like protein complex is reported [Qin \emph{et al}., Nat. Mater. \textbf{15}, 217 (2016)] to act like a compass needle to guide the magnetic orientation of animals. This view, however, is challenged [Meister, Elife \textbf{5}, e17210 (2016)] by arguing that thermal fluctuations beat the Zeeman coupling of the proteins's magnetic moment with the rather weak geomagnetic field ($\sim25-65$ $\mu$T). In this work, we show that the spin-mechanical interaction at the atomic scale gives rise to a high blocking temperature which allows a good alignment of protein's magnetic moment with the Earth's magnetic field at room temperature. Our results provide a promising route to resolve the debate on the thermal behaviors of MagR, and may stimulate a broad interest on spin-mechanical couplings down to atomistic levels.