Helical Spin Resonance in the Cubic B-20 Fe0.8Co0.2Si Single Crystal with a Long-Period Helical Spin Structure

Abstract

Electron spin resonance has been studied at various frequencies (6–24 GHz) on B-20 Fe 0.8 Co 0.2 Si single crystal, which has a long-period helical spin structure (HSS) with a cone-ferromagnetic transition at a critical field H c . Three resonance absorptions have been observed clearly: (a) behaving like a ferromagnetic resonance, (b) occuring around H c and (c) assigned to be a helical spin resonance. The resonance frequency of (c) decreases with increasing the magnetic field. Such dependence does not agree with the resonance theory for a HSS resulting from a competition between symmetric exchange interactions (SEI's), but it agrees well with that for a HSS resulting from a competition between the SEI and the antisymmetric exchange interaction. The present results together with our previous ones give the evidence that the HSS in Fe 0.8 Co 0.2 Si is of the latter type.