Nitrogen-vacancy center-based spin-echo measurement protocol to detect magnetic domain wall dynamics

The nitrogen-vacancy (NV) center in diamond is an atomic defect comprised of a vacancy adjacent to a substitutional nitrogen. The electronic spin of the negatively charged NV center (NV[-]) has widely been used in sensing and imaging magnetic fields optically. The NV[-] center electronic spin state can be initialized optically and its spin-dependent photoluminescence sensitively measured. The NV[-] spin exhibits a long coherence time even at room temperature. The spin decoherence time is mainly limited by the inhomogeneous and time-varying magnetic fields generated by surrounding paramagnetic spins and ¹³C nuclear spins. The low-frequency dephasing can be eliminated by using the Hahn spin-echo protocol. An NV[-] center close to a magnetic domain wall (DW) in a ferromagnet experiences a constant dipolar field if the DW is static throughout the Hahn echo sequence with respect to the NV[-] center. However, a moving/oscillating DW will create time-varying dipolar field sensed by the NV[-] spin. This time-varying field will cause dephasing of NV[-] spin thereby decreasing the spin-echo amplitude. A spin-echo experiment synchronized to the motion of a DW induced by a pulsed current enables the measurement of a rapidly moving magnetic texture. This method can also characterize the pinning potential through the measurement of the thermally excited dynamics of the pinned DW.