Anomalous Temperature Behavior of the Chiral Spin Helix in CrNb3 S6 Thin Lamellae

Using Lorentz transmission electron microscopy and small-angle electron scattering techniques, we investigate the temperature-dependent evolution of a magnetic stripe pattern period in thin-film lamellae of the prototype monoaxial chiral helimagnet CrNb3S6. The sinusoidal stripe pattern appears due to formation of a chiral helimagnetic order (CHM) in this material. We found that as the temperature increases, the CHM period is initially independent of temperature and then starts to shrink above the temperature of about 90 K, which is far below the magnetic phase transition temperature for the bulk material Tc (123 K). The stripe order disappears at around 140 K, far above Tc. We argue that this cascade of transitions reflects a three-stage hierarchical behavior of melting in two dimensions.