Qdev seminar by Banan El Kerdi, Université Paris-Saclay

Evidence of large Dzyaloshinskii–Moriya interaction at the cobalt/hexagonal boron nitride interface

A large Dzyaloshinskii–Moriya interaction (DMI) has been predicted to occur at the interface of Co with hexagonal boron nitride (h-BN) [1], despite h-BN being a van der Waals insulator composed of light elements.
In this seminar I will present how clean Co/h-BN interface were obtained by combining ultra-high vacuum growth and mechanical exfoliation. In addition, DMI and PMA were measured using Brillouin light scattering spectroscopy on series of samples of varying Co thickness grown on Pt or Au and covered either with h-BN or Cu. By comparing the h-BN-covered samples with their corresponding control Cu-covered samples, the effect of the Co/h-BN interface was extracted (Fig.1). We thus deduced a 𝐷𝑆𝐶𝑜/ℎ𝐵𝑁 = -0.89 pJ/m (𝐾𝑆𝐶𝑜/ℎ𝐵𝑁= 0.84 mJ/m2) and a 𝐷𝑆𝐶𝑜/ℎ𝐵𝑁 = -0.21 pJ/m (𝐾𝑆𝐶𝑜/ℎ𝐵𝑁=0.85 mJ/m2) from samples grown on Pt and Au respectively. This reveals that the Co/h-BN interface induces a large PMA and DMI comparable in strength to the largest known effects, such as those of the Pt/Co interface. The strong observed effect despite the weak spin-orbit interaction in h-BN supports a Rashba-like origin of DMI. Furthermore, the sign of DMI in Co/hBN is compatible with that of Pt/Co, resulting in an even larger DMI in Pt/Co/hBN. This enables the stabilisation of skyrmions in the Pt/Co/h-BN system, as was observed at room temperature with low magnetic fields [2], and demonstrates the interest of h-BN as functional material in the field of spintronics.

Acknowledgements
This work was supported by the Agence Nationale de la Recherche (ANR) through the project ACAF (ANR-20-CE30-0027), and by the public grant overseen by the ANR as part of the ‘Investissement d’Avenir’ programme (LABEX NanoSaclay, ANR-10-LABX-0035 SPiCY and ANR-10-LABX-0035 CHIVAWAA).
References
[1] Hallal et al., Nano Letters 21, 17 7138 (2021)
[2] El-Kerdi et al, Nano Letters 8, 3202–3208 (2023)