- The paper demonstrates that the heavy metal underlayer's 5d electron count determines the magnitude and sign of the Dzyaloshinskii-Moriya interaction in CoFeB|MgO heterostructures.
- It reveals that switching underlayers from Hf to W reverses domain wall chirality due to hybridization effects, as validated by magnetron sputtering and Kerr microscopy techniques.
- The study implies that precise interface engineering can enable efficient spintronic devices by optimizing magnetic chirality for advanced memory and storage applications.
Interface Control of the Magnetic Chirality in CoFeB|MgO Heterostructures
This paper explores the tunability of the Dzyaloshinskii-Moriya interaction (DMI) in CoFeB|MgO heterostructures, which is pivotal for advancing spintronics applications. The authors demonstrate that the DMI in these ultrathin magnetic heterostructures can be significantly influenced by the underlying heavy metal (HM) layer. Their systematic investigation covers heterostructures with heavy metal underlayers, notably Hafnium (Hf), Tantalum (Ta), Tantalum Nitride (TaN), and Tungsten (W), unveiling the role of electronic band structure characteristics in the heavy metals.
Key findings delineate that the sign and magnitude of the DMI are intricately linked to the number of 5d electrons in the HM underlayer. The paper reports that substituting the underlayer material modifies the chirality of domain walls, even though the spin Hall angle remains constant across various underlayers. Specifically, a transition from Hf to W underlayer induces a reversal in domain wall chirality, attributed to variations in electron density caused by hybridization effects at the ferromagnetic interface with CoFeB.
Nitrogen incorporation into Ta to form TaN modulates the electronic structure by influencing the hybridized orbitals, leading to further control over the DMI. This nitrogen-associated modification provides a pathway for tuning the interaction strength and chirality of domain walls. The authors substantiate these claims through magnetron sputtering deposition of films and advanced Kerr microscopy techniques for domain wall motion characterization, thereby demonstrating the feasibility of precise interface engineering.
Strong Numerical Results:
- The paper delineates a clear correlation between domain wall motion directionality and the underlying HM properties. For instance, W underlayers exhibit a domain wall motion against the electron flow, unlike Hf and Ta, which support motion along the electron flow.
- The research outlines the interface-induced DMI's dependency on the electronic configuration of the HM underlayer, specifically its 5d electron count. This is analytically reflected in the variance of DMI constants across different materials.
Implications and Speculative Outlook:
The findings offer substantial implications in the manipulation and control of magnetic chiralities, vital for the development of spintronic devices like racetrack memories and skyrmion-based storage technologies. The ability to modulate the DMI through interface engineering presents opportunities for developing lower-power, highly efficient memory elements.
This paper prompts further exploration of exotic materials and alloyed underlayers encapsulating different heavy metals to optimize the spin Hall effect and DMI for specific technological applications. Future work could focus on refining the mechanisms of spin current interaction at interfaces with non-magnetic layers, optimizing the parameters that govern the non-trivial interplay between spin-orbit coupling and crystallographic asymmetries.
In conclusion, this paper expands the understanding of magnetic chirality control within spintronic systems, presenting a methodological framework for exploiting the intrinsic magnetic phenomena through strategic material selection and interface engineering. This foundational step is anticipated to catalyze further advancements in the field, fostering innovations in the design and application of spin-based electronic devices.
