Helical Spin Resonance and Magntization Measurement in Itinerant Helimagnet FexCo1-xSi(0.3≤x≤0.85)

Measurements of electron spin resonance and magnetization have been performed on the cubic B-20 Fe x Co 1- x Si (0.3≤ x ≤0.85). The magnetization process on Fe 0.8 Co 0.2 Si indicates that this sample is a helimagnet with the cone-ferro-magnetic transition under a low magnetic field. In this sample, the helical spin resonance and the critical field resonance have been observed at 9 GHz at low temperatures, and are similar to those in MnSi observed by Date et al . The helical spin resonance data of Fe 0.8 Co 0.2 Si and MnSi are reasonably explained by the recent magnetic resonance theory for the helical spin structure due to the anti-symmetric exchange interaction existing in the cubic B-20 structure because of the lack of inversion symmetry. In every sample of Fe x Co 1- x Si, ferro- and para- magnetic resonances have been observed at 9 and 24 GHz, and are briefly discussed.