Abstract

We present the results of temperature dependent measurements of magnetically coupled Fe_1-xCr_x/Cr-superlattices. These results are supplementary to the ones known for non-collinearly coupled Fe/Cr-superlattices. By systematically varying the Cr concentration x we cover a wide range of the Fe_1-xCr_x-phase diagram. As an experimental technique spin-polarized neutron reflectivity with spin analysis and high-angle neutron scattering proves to be ideal for this work.

Author Keywords: Magnetic exchange coupling; Curie temperature; Néel temperature; Neutron reflectivity

Article Outline

1. Introduction

2. Samples

3. Experimental

4. Results

5. Conclusions

Acknowledgements

References

(22K)
Fig. 1. Reflectivity measurement with spin-polarized neutrons and spin analysis at T=35 K for a Fe_0.43Cr_0.57/Cr sample. The half order Bragg peak in R^+-(=R^-+) and no intensity splitting at the chemical first order Bragg peak position in R⁺⁺ and R^-- indicate an AFM coupling perpendicular to the neutron polarisation axis. The high intensity in R⁺⁺ and R^-- at the half order position is related to a high diffuse magnetic scattering which was confirmed with off specular scans. The inset documents the magnetic reorientation from AFM to FM by its temperature-dependent splitting. For more details see text.

Table 1. List of [Cr/Fe_1-xCr_x]_N/Cr/Nb/(1 Not-found 0 2)Al₂O₃ samples with systematic variation of the Cr concentration x. The samples were grown under equivalent conditions by molecular beam epitaxy. The spacer layer thicknesses, t_Cr<45 Å, was chosen to assure a commensurate AF spin structure. The large number of superlattice periods increases the amount of Cr which improves the signal to background ratio in neutron scattering experiments. The measured Curie temperatures for samples with higher concentrations are considerably lower than the bulk values (<1K)

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Correspondence address: Institut Laue–Langevin, 38042 Grenoble cedex 9, France. Tel.: +33-4-76-20-75-89; fax: +33-4-76-20-71-20; email: siebrech@ill.fr