Nanomaterials: Application & Properties, 9th International Conference on Nanomaterials: Applications & Properties '2019

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Diffusion and Phase Transformations in Annealed Pt/Mn/Fe Trilayers
Ivan O. Kruhlov, Manfred Albrecht, Oksana Shamis, Igor Vladymyrskyi, Nataliia Schmidt

Last modified: 2019-08-25

Abstract


Chemically ordered L10-FePt is a very interesting magnetic material providing a variety of different applications. For instance, FePt thin films are currently implemented as storage material for application as heat-assisted magnetic recording (HAMR) media with ultra-high density. Furthermore, high perpendicular magnetic anisotropy (PMA) and Curie temperature as well as excellent corrosion resistance are distinctive to this phase allowing for further applications in perpendicular magnetic tunnel junctions [1], magnetic micro-electro-mechanical systems (MEMS) [2], and new-type thermopiles [3, 4]. Althought, the reduction in Curie temperature while maintaining strong PMA is still a relevant task for FePt film applications. In this regard, Mn was considered as a doping element for L10-FePt [5]. However, solid-state reactions and diffusion regularities in FePt-Mn films requires further studies.

In this study, Pt(15 nm)/Mn(7.5 nm)/Fe(15 nm)/sub. thin films were deposited by dc magnetron sputtering on thermally oxidized Si(100) substrates with a 100 nm-thick amorphous SiO2layer at room temperature. As-deposited films were annealed in the temperature range of 155-620 °C in vacuum (10-3Pa) with an average heating rate of 0.5 °C/s.Sequence of thermally-activated phase transitions in Pt/Mn/Fe thin films was investigated by combination of x-ray diffraction (XRD), transmission electron microscopy (TEM), energy-dispersive x-ray spectroscopy (EDX) point scanning, secondary neutral mass spectrometry (SNMS) depth profiling, atomic force microscopy (AFM), and magnetic properties measurements.

At first, after annealing at 280 °C the ordered binary L10-PtMn phase was formed and pronounced Mn surface segregation was registered. Fe unreacted layer remains in the film at these temperatures, dominating the materials magnetic properties. The following increase of the heat treatment temperature up to 450 °C results in the formation of FeMn solid solution with antiferromagnetic order and ferromagnetic L10-PtMnFe phase, resulting in drastic decrease of films saturation magnetization (Fig. 1). The following rise of heat treatment temperature leads to dissolution of the FeMn phase and formation of the ferromagnetic Fe3Pt compound. There is a coexistence of ternary PtMnFe and binary Fe3Pt phases after final annealing stage at 620 °C.

References

[1] Kohn A., Tal N., Elkayam A., Kovacs A., Li D., Wang S., Ghannadzadeh S., Hesjedal T., and Ward R.C.C. 2013 Appl. Phys. Lett. 102 062403.

[2] Rhen F.M.F., Hinds G., O'Reilly C., and Coey J.M.D. 2003 IEEE Trans. Magn. 39 2699.

[3] Mizuguchi M., Ohata S., Uchida K., Saitoh E., and Takanashi K. 2012 Appl. Phys. Express 5 093002.

[4] Hasegawa K., Mizuguchi M., Sakuraba Y., Kamada T., Kojima T., Kubota T., Mizukami S., Miyazaki T., and Takanashi K. 2015 Appl. Phys. Lett. 106 252405J.

[5] Xu D.B., Chen J.S., Zhou T.J., and Chow G.M. 2011 J. Appl. Phys. 109 07B747.


Keywords


thin films, PtMnFe, L10, magnetic media, diffusion