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

Abstract

The in-plane Fe spin spiral structure for Fe/Sm-Co(1100) exchange-spring magnetic bilayers was investigated by 57 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.

Noncollinear Fe spin structure in (Sm-Co)/Fe exchange-spring bilayers: Layer-resolved57Fe Mössbauer spectroscopy and electronic structure calculations

“…(2), the model-independent average quantity Often experimental values of R 23 are compared with theoretical R 23 ratios simulated on the basis of reasonable model distributions P(φ) [11,20]. The simplest model implies the unidirectional distribution P(φ) with a unique Fe spin direction.…”

“…A more realistic model uses a step-shaped planar distribution P(φ), where the in-plane spins are assumed to be located in a certain angular interval and show homogeneous fanning. This model was employed to deduce the Fe spin structure in Fe/MnF 2 exchange-biased bilayers [21] and in (Sm-Co)/Fe bilayer spring magnets [11]. However, in the present work we do not need to use a specific model for the distribution P(φ).…”

“…R 23 can be calculated using eq. (2) with: take into account the weak attenuation of the conversion electron response due to the effects of scattering and absorption before escaping from the sample surface [11]. The coefficient p Fe describes the weakening of the electron yield per one Fe monolayer with increasing depth.…”

“…For the energyintegrated conversion electron transmission versus depth z we have employed the transmission function ("weight function") T t (z) given by Liljequist et al [33], as described in Ref. 11. However, as a somewhat better approximation than in Ref.…”

“…The Co layers, deposited either at the interface or at the top of the NiFe film, were analyzed using the soft-x-ray magneto-optical Kerr effect at the Co L-edge resonance. Kuncser et al [11] and Keune et al [12] utilized conversion electron Mössbauer spectroscopy (CEMS), incorporating the 57 Fe probe layer technique, to reveal the spin structure in layered Sm-Co/Fe exchange spring systems.…”