Room temperature chiral magnetic skyrmion in ultrathin magnetic nanostructures (1601.02278v1)

Abstract: Magnetic skyrmions are chiral spin structures with a whirling configuration. Their topological properties, nanometer size and the fact that they can be moved by small current densities have opened a new paradigm for the manipulation of magnetisation at the nanoscale. To date, chiral skyrmion structures have been experimentally demonstrated only in bulk materials and in epitaxial ultrathin films and under external magnetic field or at low temperature. Here, we report on the observation of stable skyrmions in sputtered ultrathin Pt/Co/MgO nanostructures, at room temperature and zero applied magnetic field. We use high lateral resolution X-ray magnetic circular dichroism microscopy to image their chiral N\'eel internal structure which we explain as due to the large strength of the Dzyaloshinskii-Moriya interaction as revealed by spin wave spectroscopy measurements. Our results are substantiated by micromagnetic simulations and numerical models, which allow the identification of the physical mechanisms governing the size and stability of the skyrmions.

• The paper reports the experimental detection of room temperature chiral skyrmions in sputtered Pt/Co/MgO nanostructures using high-resolution XMCD-PEEM.
• The paper establishes that strong spin-orbit interaction and lateral confinement stabilize skyrmions with an approximate 130 nm diameter at zero magnetic field.
• The paper integrates micromagnetic simulations and spin wave spectroscopy to elucidate the interplay between exchange, anisotropy, and DMI, advancing spintronic applications.

Room Temperature Chiral Magnetic Skyrmion in Ultrathin Magnetic Nanostructures

The paper titled "Room temperature chiral magnetic skyrmion in ultrathin magnetic nanostructures" presents a significant exploration into the observation and control of magnetic skyrmions at room temperature in sputtered ultrathin Pt/Co/MgO nanostructures. Skyrmions, topologically stable swirling spin structures, show promise for advancing magnetic memory and logic devices due to their stability, nanometer scale, and efficient mobility under low current densities. Unlike previous demonstrations, which were largely restricted to low temperatures or required external magnetic fields, this research provides evidence of skyrmions' stability at room temperature and zero field.

Key Research Findings

• Experimental Observation: Using high-resolution X-ray magnetic circular dichroism (XMCD-PEEM), the authors successfully detected the internal chiral N\'eel structure of skyrmions. The presence of a Dzyaloshinskii-Moriya interaction (DMI) was substantiated by spin wave spectroscopy, contributing to the stability of the skyrmions observed.
• Material and Technique Excellence: The Pt/Co/MgO stack was chosen for its capability to support a significant DMI due to strong spin-orbit interaction and lack of inversion symmetry. Techniques such as micromagnetic simulations corroborated the experimental results, providing insights into the mechanisms governing skyrmion size and stability.

Experimental and Theoretical Analysis

The paper combines experimental observations with detailed simulations to map out the magnetic structures and interactions within the nanostructures. The following points delineate the experimental setup and computation:

• Spin Wave Spectroscopy: Using Brillouin light scattering, the paper determines the DMI's contribution to the spin wave spectrum's asymmetry, extracting a DMI strength of 2.05 mJ/m$^2$.
• Skyrmion Stability and Size: Micromagnetic simulations predict stable skyrmion structures at zero magnetic field, matching the experimental diameter of approximately 130 nm. The simulations utilized an exchange constant $A = 27.5$ pJ/m, significantly influencing the skyrmion's energy balance between exchange, anisotropy, and magnetostatic interactions.
• Impact of Lateral Confinement: The simulations revealed that geometric confinement within nanodots plays a crucial role in stabilizing skyrmions, corroborating experimental observations in structures under 1.2 µm in lateral dimension.

Implications and Future Work

The ability to stabilize skyrmions at room temperature without an external magnetic field is pivotal for their potential application in novel high-density, low-power memory devices. By understanding these interactions and skyrmion properties, the paper opens avenues for optimized device architecture and industrial application using standard sputtering techniques.

Prospective work could focus on refining the control over skyrmion dynamics and exploring diverse material combinations that maximize DMI and skyrmion mobility for practical applications. Moreover, attention to skyrmion dynamics under smaller current densities or alternate polarities may further unveil their potential for spintronic applications.

Conclusion

This research marks a crucial step in the development of magnetic skyrmion technology. The stability of skyrmions at ambient conditions and their detailed characterization through experimental and simulation approaches bolster their credentials as promising candidates for the next generation of spintronic devices. The work sets a foundation to transition these findings from the laboratory into commercially viable technologies.