Magnetic field evolution of magnetic order in a chiral helimagnet as revealed by second harmonic generation

Cr_1/3NbS₂ crystallizes in a chiral crystal structure, allowing for physical quantities that transform as structural chirality, such as the monoaxial Dzyaloshinskii-Moriya interaction (DMI). This antisymmetric DMI interaction competes with the symmetric exchange interaction to form chiral magnetic order. In the presence of a small external magnetic field applied within the easy plane, the chiral helimagnetic phase crosses over to a rich chiral soliton lattice phase, making Cr_1/3NbS₂ an interesting platform to study the interaction between magnetic field and noncollinear magnetism. In this work, we utilize rotation anisotropy second harmonic generation (RA-SHG) as a local and surface-sensitive probe for the formation of chiral spin textures in Cr_1/3NbS₂. Through external magnetic field-dependent measurements, we observe multiple distinct regimes with differing RA-SHG responses and examine the evolution of the response within each regime, shedding light on the nature of the noncollinear magnetic textures represented in the rich magnetic phase diagram.