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PRINCIPAL PUBLICATION AND AUTHORS

A three-dimensional analysis of magnetic nanopattern formation in FeRg thin films on MgO substrates: Implications for spintronic devices, D.G. Merkel (a,b), G. Hegedűs (a), M. Gracheva (b,c), A. Deák (b), L. Illés (b), A. Németh (a), F. Maccari (d), I. Radulov (d), M. Major (a,d), A.I. Chumakov (e), D. Bessas (e), D.L. Nagy (a), Z. Zolnai (b), S. Graning (f,g), K. Sájerman (f), E. Szilágyi (a), A. Lengyel (a), ACS Appl. Nano Mater. 5, 5516-5526 (2022); https:/doi.org/10.1021/acsanm.2c00511 (a) Wigner RCP, Budapest (Hungary) (b) Centre for Energy Research, Budapest (Hungary) (c) Institute of Chemistry, Eötvös Loránd University, Budapest (Hungary) (d) Technische Universität Darmstadt, Darmstadt (Germany) (e) ESRF (f) Institute of Physics, Budapest University of Technology and Economics, Budapest (Hungary) (g) Institute of Physics, Eötvös Loránd University, Budapest (Hungary)

REFERENCES

[1] D.G Merkel et al., Sci. Rep. 10, 1-11 (2020). [2] Y. Liu et al., Nat. Comm. 7, 1-6 (2016). [3] A.M Tishin et al., Int. J. of Refrig. 68, 177-186 (2016). [4] I. Astefanoaei et al., J. Appl. Phys. 115, 17B531 (2014).

results show unusual magnetic domain profiles as a result of depth-dependent effects: if the Ne+ ions hit off-centre of the sphere, they are able to reach the sample surface with reduced energy and may turn FM regions to PM directly below the upper surface. Indeed, this effect is responsible for the narrowing of the upper part of magnetic domains. The continuous contraction of the magnetic area towards the bottom of the FeRh film stems from lateral straggling of the ions, which increases with penetration depth. Finally, if the incoming ion hits the very edge of the sphere, its

trajectory may be deviated and the ion can directly reach areas under the mask.

In conclusion, the presented results can be applied for engineering tailored FM regions in a PM matrix by means of custom irradiation masks. Ne+ ion irradiation of FeRh films can also assist in the direct writing of FM areas with the help of focused ion-beam lithography. It was also shown that the variation of in-depth magnetism must be considered when device development is based on this method.

Magnetic phase probing by polarisation analysis in Mössbauer reflectivity

Polarisation analysis of the reflected radiation in Mössbauer reflectivity sheds new light on the magnetic state of iron in thin films and multilayers. It opens a new way to simplify the shape of the resonance spectra and select the contributions from ferromagnetically ordered phases excluding the input from phases with zero net magnetisation.

Construction of the Synchrotron Mössbauer Source at beamline ID18 has ensured the effective development of Mössbauer reflectivity experiments. Mössbauer reflectivity spectra measured at various grazing angles contain depth-resolved information about the chemical and magnetic structure of ultrathin films and multilayers with sub-nanometre resolution [1,2]; however, their interpretation is not simple. Polarisation analysis of the reflected beam [3] opens a way to simplify the shape of the Mössbauer spectrum and select the contributions from ferromagnetically ordered phases, excluding the input from phases with zero net magnetisation (antiferromagnetic, paramagnetic, etc...).

To probe the sensitivity of the polarisation analysis to different magnetic phases, measurements were performed

at beamline ID18, making use of the purely p-polarised radiation from Synchrotron Mössbauer Source. A [57Fe(10 ML)/V (20 ML)]20 multilayer deposited on a MgO (0 0 1) substrate was tested. Radiation with the rotated p→s polarisation was selected by ~ 90o reflection from a LiF (6 2 2) crystal (Figure 20). Mössbauer reflectivity spectra with and without polarisation selection were measured at two angles: (i) near the critical angle (θ=0.22°), where X-rays only penetrate for a few nanometres (Figure 21a), and (ii) at the Bragg angle (θ=0.58°), where X-rays test the whole multilayer (Figure 21b). The spectra were obtained with the external field Bext = 1 T applied along the beam direction, high enough for the practically complete alignment of the ferromagnetic phase but not enough for spin-flip in antiferromagnetic phases.

Fig. 20: Schematic setup of the Mössbauer reflectivity experiment with p→s` polarisation selection.