Effect of Surface Oxidation and Crystal Thickness on the Magnetic Properties and Magnetic Domain Structures of Cr₂Ge₂Te₆

Journal Article · 13 May 2024 · ACS Nano

DOI: https://doi.org/10.1021/acsnano.3c09858 · OSTI ID:2403444

Thomsen, Joachim Dahl  ^[1]; Han, Myung-Geun  ^[2]; Penn, Aubrey N. ^[3]; Foucher, Alexandre C. ^[3]; Geiwitz, Michael ^[4]; Burch, Kenneth S. ^[4]; Dekanovsky, Lukas ^[5]; Sofer, Zdeněk ^[5]; Liu, Yu ^[6]; Petrovic, Cedomir ^[7]; Ross, Frances M. ^[3]; Zhu, Yimei ^[2]; Narang, Prineha ^[8]

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1. Univ. of California, Los Angeles, CA (United States); Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
2. Brookhaven National Laboratory (BNL), Upton, NY (United States)
3. Massachusetts Inst. of Technology (MIT), Cambridge, MA (United States)
4. Boston College, Chestnut Hill, MA (United States)
5. University of Chemistry and Technology, Prague (Czech Republic)
6. Brookhaven National Laboratory (BNL), Upton, NY (United States); Zhejiang Univ., Hangzhou (China)
7. Brookhaven National Laboratory (BNL), Upton, NY (United States); Shanghai Advanced Research in Physical Sciences (SHARPS), Shanghai (China)
8. Univ. of California, Los Angeles, CA (United States)

van der Waals (vdW) magnetic materials, such as Cr₂Ge₂Te₆ (CGT), show promise for memory and logic applications. This is due to their broadly tunable magnetic properties and the presence of topological magnetic features such as skyrmionic bubbles. A systematic study of thickness and oxidation effects on magnetic domain structures is important for designing devices and vdW heterostructures for practical applications. Here, we investigate thickness effects on magnetic properties, magnetic domains, and bubbles in oxidation-controlled CGT crystals. We find that CGT exposed to ambient conditions for 5 days forms an oxide layer approximately 5 nm thick. This oxidation leads to a significant increase in the oxidation state of the Cr ions, indicating a change in local magnetic properties. This is supported by real-space magnetic texture imaging through Lorentz transmission electron microscopy. By comparing the thickness-dependent saturation field of oxidized and pristine crystals, we find that oxidation leads to a nonmagnetic surface layer that is thicker than the oxide layer alone. We also find that the stripe domain width and skyrmionic bubble size are strongly affected by the crystal thickness in pristine crystals. Finally, these findings underscore the impact of thickness and surface oxidation on the properties of CGT, such as saturation field and domain/skyrmionic bubble size, and suggest a pathway for manipulating magnetic properties through a controlled oxidation process.

• Research Organization: Brookhaven National Laboratory (BNL), Upton, NY (United States); National Quantum Information Science (QIS) Research Centers (United States). The Quantum Science Center (QSC)
• Sponsoring Organization: USDOE Office of Science (SC), Basic Energy Sciences (BES). Materials Sciences & Engineering Division (MSE); US Air Force Office of Scientific Research (AFOSR)
• Grant/Contract Number: SC0012704; SC0022277; SC0018675
• OSTI ID: 2403444
• Report Number(s): BNL--225823-2024-JAAM
• Journal Information: ACS Nano, Journal Name: ACS Nano Journal Issue: 21 Vol. 18; ISSN 1936-0851
• Publisher: American Chemical Society (ACS)Copyright Statement
• Country of Publication: United States
• Language: English