Discipline: Nanoscience or Materials Science
Subcategory: Materials Science
Candice Forrester - The Graduate Center
Co-Author(s): Ido Levy, CUNY Graduate Center, New York, NY; Gabriel Lopez-Morales CUNY Graduate Center, New York, NY; Xiaxin Ding, The City College of New York, New York, NY; Kaushini Wickramasinghe, The City College of New York, New York, NY; Christophe Testelin, Sorbonne Université, CNRS, Institut des NanoSciences de Paris, F-75005 Paris, France; Lia Krusin, The City College of New York, New York, NY; Gustavo Lopez, Lehman College, New York, NY; Maria Tamargo, The City College of New York, New York, NY
The interaction between magnetic impurities and topological electronic states of 3D topological insulators (TIs) has attracted many studies of predicted exotic phenomena, which may lead to the observance of quantum anomalous hall effect (QAHE) and realizations of quantum computing, among others.1 Mixing of Mn, Sb and Te during crystal growth by bulk growth or epitaxial techniques forms a new crystal phase, MnSb2Te4, with septuple layer (SL) units rather than typical quintuple layer (QL) units of the undoped TIs. These magnetic TIs display antiferromagnetic (AFM) behavior in bulk, which is not conducive for QAHE, and typically have high bulk conductivity, which limits the ability to detect the surface states and their possible applications. Previously, our group showed that we can control (MnSb2Te4)x(Sb2Te3)1-x structures by optimizing Mn incorporation and inducing FM coupling.2 These structures exhibit ferromagnetic (FM) behavior and a reduced bulk conductivity depending on the %SLs in the structure. (MnSb2Te4)x(Sb2Te3)1-x samples with 70-85% SL high Curie temperatures (TC) as high as 80K were observed. Here we report further enhancement of the TC and magnetic coupling by modifying the MBE growth conditions: Mn beam equivalent pressure (BEP) ratios and growth rates varied in this study. Increasing Mn BEP ratio yielded increased TC values in samples with 70-80%SL. Reducing Mn BEP ratio to levels of 0.04-0.06 showed evidence of the coexistence of FM and AFM phases, suggesting the approach to stoichiometric MnSb2Te4 growth, with little excess Mn. Samples with a lower growth rate of about 0.5-0.6 nm/min, compared to ~0.9-1.0 nm/min used previously, and with Mn BEP ratios 0.09, resulted in structures having 79-89% SLs that also exhibit two distinct TC values, one TC value (TC1) at ~40-50K and a high TC value (TC2) of 100K and above. These high TC values are significantly higher than any values reported to date for these materials. We will present these results as they relate to the (MnSb2Te4)x(Sb2Te3)1-x structural properties and the details of the growth mechanism.
Funder Acknowledgement(s): CREST-IDEALS (HRD-2112550) PAQM (DMR-2011738)
Faculty Advisor: Maria C. Tamargo, firstname.lastname@example.org
Role: In this study, I was responsible for growing the samples using molecular beam epitaxy, characterizing them using Xray diffraction, Hall effect analysis and organizing meetings to discuss results. It was also my duty to analyze my data using Origin software.