Observation of the Fe spin spiral structure in Fe/Sm-Co exchange-spring bilayers by Mössbauer spectroscopy

The in-plane Fe spin spiral structure for $\mathrm{F}\mathrm{e}/\mathrm{S}\mathrm{m}-\mathrm{C}\mathrm{o}\left(11\mathrm{}¯00\right)$ exchange-spring magnetic bilayers was investigated by ${}^{57}\mathrm{Fe}$ conversion electron Mössbauer spectroscopy during the magnetization reversal process, and correlated with hysteresis loops measured via the longitudinal magneto-optic Kerr effect. A direct experimental proof for a relaxed spiral angular spin distribution in the Fe layer is presented. Under negative applied fields the interfacial Fe spins rotate by up to $40°$ with respect to the easy axis of the Sm-Co hard-magnet layer.