Crystallization of magnetic skyrmions in MnSi investigated by neutron spin echo spectroscopy

We performed neutron resonance spin echo measurements on MnSi to investigate how the magnetic skyrmions crystalize into a lattice on cooling in a magnetic field. We found that the skyrmions aggregate into small skyrmion-lattice (SkL) domains with orientational disorder upon the transition from the paramagnetic phase to the SkL phase. These domains are nearly static in time, and coexist with chiral spin fluctuations with a characteristic relaxation time of 10(-9) s near the transition temperature. As the temperature is further decreased, the SkL domains merge into the long-range-ordered SkL. These observations provide a microscopic picture of the crystallization of the magnetic skyrmions.