The next online seminar of the Joint Brazil-Spain Seminars in Magnetism and Magnetic Materials series organised by the Club Espanol de Magnetismo (CEMAG) will be given by Prof. Ângela Burlamaqui Klautau on Thursday 8 June at 16:00 (Spain local time).

• The title and abstract are attached below .
• Google Meet link is meet.google.com/wji-bfjx-hex

Exploring the role of interfacial atomic defects in the skyrmions formation

Prof. Ângela Burlamaqui Klautau
Faculdade de Física, Universidade Federal do Pará (UFPA), Belém-PA, Brazil.

Abstract

To achieve next-generation spintronic devices based on the so-called skyrmionics, the classification and analysis of skyrmion-hosting materials and their conditions for the emergence of complex magnetic textures are necessary. Spontaneous room temperature skyrmions in Pd/Co/Pd multilayers have recently been experimentally reported [1]. Interestingly, despite the presence of inversion symmetry, a non-zero Dzyaloshinskii-Moriya interaction (DMI) was measured, potentially explaining the stabilization of these skyrmions at room temperature, along with a large perpendicular magnetic anisotropy (PMA). Here, using a multiscale theoretical approach that combines ab-initio electronic structure calculations [2-4] and state-of-the-art atomistic spin dynamics simulations [5], we present an investigation of Pd/Co/Pd multilayers with a focus on the magnetic configuration obtained using the Heisenberg exchange and Dzyaloshinskii-Moriya interactions, exploring the influence of the DMI on the ground state and at room temperature. We unveil the presence of metastable skyrmionicstates in these nominally symmetric multilayers, attributed to the significant enhancement of DMI strength due to interfacial atomic defects. Notably, these metastable skyrmions emerge without the need for external magnetic fields and remain stable even near room temperature conditions. Our theoretical findings corroborate with magnetic force microscopy and X-ray magnetic circular dichroism measurements, underscoring the potential for fine-tuning DMI intensity through interdiffusion at thin film interfaces [6]. In addition to the well-known skyrmion, another magnetic structure of interest is the skyrmionium, composed of two skyrmions with opposite winding numbers, resulting in a total zero topological charge. This property allows the skyrmioniums to move by the action of a spin-polarized current without any undesirable lateral motion. Here, using the same theoretical methodology [2-5], we present a prediction of both stable skyrmions and unusual metastable skyrmioniums in Ni/Irn/Pt(111) ultrathin films (with n = 0, 1, 2) [3]. Fundamental interactions that control these nanostructures are calculated, as well as some of the properties as a function of enhancing the Ir buffer thickness, particularly: size, speed, and stability with the application of external magnetic fields and finite temperatures.

References

1.  J. Brandão et al., Observation of magnetic skyrmions in unpatterned symmetric multilayers at room temperature and zero magnetic field. Scientific Reports 2019, 9, 4144.
2.  S. Frota-Pessôa, Phys. Rev. B 46, 14570 (1992).
3.  P. C. Carvalho et al., Complex magnetic Ni/Irn /Pt(111) ultrathin. Phys. Rev. Materials 2021, 5, 124406.
4.  I. P. Miranda, et al., Band filling effects on the emergence of magnetic skyrmions: Pd/Fe and Pd/Co bilayers on Ir(111). Phys. Rev. B 2022, 105, 224413.
5.  B. Skubic et al., J. Phys. Cond. Matt. 20, 315203 (2008).
6.  P. C. Carvalho et al., Correlation of interface interdiffusion and skyrmionic phases. Accepted to Nano Letters (https://doi.org/10.1021/acs.nanolett.3c00428).