Abstract

The influence of Ar-ion irradiation on the microstructure, interlayer coupling and magnetoresistance in Fe/Cr multilayers is studied. An increase of interface roughness of Fe/Cr multilayers caused by irradiation with 200 keV Ar ions and doses exceeding 5 × 10¹² Ar/cm² is clearly seen in conversion electron Mössbauer spectroscopy (CEMS) measurements, while the small angle X-ray diffraction (SAXRD) technique hardly detects such changes in microstructure even at the higher ion doses. This subtle modification of the microstructure induces distinct changes in magnetization reversal (increase of the remanence magnetization, decrease of the saturation fields) and strongly decreases GMR effect with increasing irradiation dose. The most prominent changes are observed for the samples with a small thickness of Cr layers. The increasing immunity of GMR effect to ion irradiation with the increasing thickness of Cr layers as well as correlation between changes in GMR and antiferromagnetically coupled sample fraction suggest that the main effect responsible for the decrease of GMR is caused by the pinholes creation. For doses exceeding 2 × 10¹³ Ar/cm² the volume intermixing seems to be a dominating mechanism responsible for further degradation of GMR and antiferromagnetic interlayer exchange coupling.

Author Keywords: Magnetic multilayers; Interlayer coupling; Giant magnetoresistance; Mössbauer spectroscopy; Magnetic films and multilayers; Magnetic measurements; Irradiation; Argon; Electronic transport; Nuclear resonances

Article Outline

1. Introduction

2. Experiment

3. Results and discussion

4. Conclusions

Acknowledgements

References

(8K)
Fig. 1. Spectral fractions of HF₁–HF₄ components vs. ion dose for Fe-1.4 nm/Cr-t_Cr multilayers with t_Cr = 0.97 nm (), t_Cr = 1.03 nm (•), t_Cr = 1.4 nm (), t_Cr = 1.5 nm (), t_Cr = 1.85 nm (). The lines are guides to the eye.

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Fig. 2. Hysteresis loops of as-deposited Fe-1.4 nm/Cr-t_Cr multilayers with different thickness of Cr spacer.

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Fig. 3. Exemplary SAXRD spectra taken for as-deposited and irradiated sample (Fe-3 nm/Cr-1.1 nm). The curves are vertically shifted (by one decade) for clarity.

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Fig. 4. Examples of hysteresis loops and GMR(H) dependences for as-deposited and irradiated Fe-1.4 nm/Cr-t_Cr samples with t_Cr = 0.97 nm (a, b), t_Cr = 1.4 nm (c, d), t_Cr = 1.55 nm (e, f). The description of curves 1, 2 and 3 denote samples in as-deposited state and irradiated with doses 2 × 10¹³ and 8 × 10¹³ Ar/cm², respectively.

(14K)
Fig. 5. The dependences of saturation field H_S, GMR value, antiferromagnetically coupled fraction F_AF and GMR/F_AF of Fe-1.4 nm/Cr-t_Cr multilayers as a function of t_Cr for the as-deposited samples () and after successive irradiation with doses 5 × 10¹² Ar/cm² (•); 1 × 10¹³ Ar/cm² (); 2 × 10¹³ Ar/cm² (); 8 × 10¹³ Ar/cm² (); 1.2 × 10¹⁴ Ar/cm² ().

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