Magnetic relaxation between ferromagnetic and helix spin configurations in holmium films

Abstract

Multiple noncollinear spin structures and transitions between them initiated by field and temperature attract attention due to extraordinary coexistence of complicate spin phases in Ho. We explore the magnetic relaxation dynamics within thin films undergoing transitions between ferromagnetic (FM) and helix states. Employing susceptibility measurements at a relatively high frequency range (~100-1500 Hz) and magnetic viscosity measurements at a lower frequency (~0.01 Hz), we focus on Ho films with a thickness of 400 nm. Notably, sharp variations in the real and imaginary components of magnetic susceptibility are discerned during the FM—Helix transition, occurring at temperatures between 15-30 K. Hysteresis effects in the magnetic susceptibility components are identified during cyclic variations in the external field, indicating a relatively rapid process with a timescale of approximately 10 ms accompanying the FM—Helix transition. The slow relaxation process is also found to exhibit sensitivity to this transition. Furthermore, the field dependence of magnetic viscosity displays a marked decline at the FM—Helix transition. The proposed research methodologies for investigating relaxation processes in materials with multiphase spin structures are deemed universally applicable and offer insights into transitions between spin states in materials manifesting non collinear spin structures.