Abstract

We introduce a new method to image the internal spin structure in exchange-coupled thin films. The technique relies on nuclear resonant scattering of synchrotron radiation from ultrathin layers of Mössbauer isotopes embedded in different depths of the sample. The technique is applied to image the spiral spin structure that forms in exchange-spring bilayers in external magnetic fields.

Author Keywords: Exchange coupling; Spin structure; Probe layers; Synchrotron radiation; Nuclear resonance; Mössbauer effect

75.70.−i; 75.25.+z; 76.80.+y; 61.10.−i

Article Outline

1. Introduction

2. The experimental method

3. The magnetic structure of exchange-spring bilayers

4. Conclusion and outlook

Acknowledgements

References

(18K)
Fig. 1. Top: Scattering geometry applied to investigate the magnetic spin structure in Fe/FePt exchange-spring bilayers. In the soft-magnetic Fe layer, an isotopic probe layer of ⁵⁷Fe is embedded. Bottom: For selected orientations of the magnetization relative to the wavevector of the incident photon, the time spectra I(t) of nuclear resonant scattering are shown. and are the vectors of the polarization basis.

(43K)
Fig. 2. Top: Measured time spectra of grazing incidence reflection in a perpendicular magnetic field of H=160 mT at various lateral positions Δx. The change in the beat pattern reflects the rotation of the magnetization direction as a function of depth D. Solid lines are theoretical simulations from which the rotation angle , as defined in Fig. 1, was derived. Bottom: Depth dependence of the spin rotation in the Fe layer for external magnetic fields of 160 mT (&z.cirf;), 240 mT (), and 500 mT (). Lines are simulations according to the model described in [15] with the magnetic parameters given in the text.

(17K)
Fig. 3. Effect of the hyperfine field distribution on the measured time spectra. (a) Simulation of the time spectra with a single hyperfine field of 33.8 T; (b) Simulation of the same data with an additional field distribution around 27 T as shown above; (c) Depth dependence of the relative fraction of the corresponding magnetization component.

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