A centrosymmetric hexagonal magnet with superstable biskyrmion magnetic nanodomains in a wide temperature range of 100K to 340K (1605.06186v1)

Abstract: Here, we report on the experimental discovery of biskyrmion magnetic nanodomains at RT and the observation of a biskyrmion-derived topological Hall effect (THE) in the centrosymmetric hexagonal MnNiGa magnet. Using a phase reconstruction technique based on a transport-of-intensity equation (TIE), we established the texture of the biskyrmion spin. Results from Lorentz transmission electron microscopy (TEM) and the topological Hall effect revealed that the biskyrmion phase is stable over a much wider temperature range (100 K to ~340K) and a larger magnetic field range in our material than in skyrmion-hosting bulk crystals reported previously[1-3,6]. The super-wide operating temperature and the broad range of material options indicate important progress toward the realization of skyrmion-based spintronic devices.

• The paper demonstrates the discovery of room-temperature biskyrmions in a centrosymmetric MnNiGa hexagonal magnet, broadening material options for spintronics.
• Methodology involved synthesizing MnNiGa alloys and employing X-ray diffraction, Lorentz TEM, and Hall resistivity to identify and characterize the biskyrmion phase.
• Findings reveal a reversible transition from helical to biskyrmion states and highlight their stability over a wide temperature range, suggesting promising applications in magnetic storage.

Stability of Biskyrmion Magnetic Nanodomains in MnNiGa

Introduction

The paper of magnetic skyrmions has intensified due to their potential applications in spintronic devices. These topologically protected spin textures offer unique avenues for information storage and processing. Typically, skyrmions have been found in non-centrosymmetric materials driven by Dzyaloshinskii-Moriya interactions. However, the current paper reports the discovery of biskyrmion magnetic nanodomains within a centrosymmetric MnNiGa hexagonal magnet, extending the possible material classes for hosting such spin structures.

Methodology

A series of MnNiGa alloys were synthesized, particularly focusing on the composition with x = 0.5 due to its desirable Curie temperature and magnetic properties. The synthesis involved arc-melting mixtures of high-purity Mn, Ni, and Ga, with structural features confirmed via powder X-ray diffraction and Rietveld refinements. Magnetic and transport properties were evaluated using a four-probe method, while magnetic domains were observed with Lorentz transmission electron microscopy (TEM). Hall resistivity measurements were used to identify the presence of the topological Hall effect (THE).

Observation of Biskyrmions

This paper builds upon previous work, demonstrating biskyrmion magnetic nanodomains at and above room temperature, specifically in the range of 100K to 340K. This is broader than previously identified ranges in related systems. The biskyrmion phase was confirmed using a combination of Lorentz TEM imaging and transport measurements, including the observation of a THE, which serves as an indicator of skyrmion presence, attributed to the spin chirality in the material.

Magnetic Characteristics

The MnNiGa compound, noted for its hexagonal Ni2In-type structure, exhibited a stable biskyrmion phase with adaptations in magnetic field and temperature. Lorentz TEM images mapped the emergence and stability of these domains under varied magnetic fields. The transformation from helical to biskyrmion configurations commenced at a certain threshold, reversible upon further field increase, which also led to the collapse of biskyrmions into ferromagnetic states.

Spin Texture Analysis

The spin texture analysis verified that biskyrmions comprise two intertwined skyrmions with opposing helicities, a trait unique to centrosymmetric systems. The paper examined the spin textures using TIE analysis of the Lorentz TEM data, revealing critical insights into the stability and formation mechanisms of biskyrmions in this non-cubic, centrosymmetric material.

Implications and Future Directions

The identification of room temperature biskyrmions in MnNiGa expands the potential landscape of skyrmionics. The broad temperature range over which these biskyrmions are stable opens new opportunities for practical spintronic device applications. Furthermore, it suggests avenues for exploring other centrosymmetric materials that may host skyrmions, guiding future materials synthesis and characterization efforts. Future work may involve expanding studies to the microscopic dynamics of biskyrmion formation, stability under varying influences, and potential exploitation in quantum and topological transport phenomena.

Conclusion

This research underscores the versatility and technological promise of biskyrmionic states in spintronics, demonstrating the need for deeper material exploration beyond the established chiral magnetic systems. The findings set the stage for accelerated innovation in designing magnetic storage and processing technologies that capitalize on the unique topological stability offered by biskyrmions.