arXiv subjects

Maria C. Tamargo

Publications and source records attributed to Maria C. Tamargo.

6 recordsLinked to original sources

arXiv2026

Magnetic interactions and origin of high Curie temperatures in high Mn content (MnSb2Te4)x(Sb2Te3)1-x quantum materials

Understanding the magnetic interactions that promote high TC in topological quantum materials is essential to effectively design materials whose magnetic configuration persists at high temperatures and are thus practical to integrate into commercial spintronic devices. Here we provide evidence of the origin of the high TC observed in mixed Mn1+ySb2-yTe4 septuple layers and Sb2-yMnyTe3 quintuple layer structures. Analysis of the quintuple layer/septuple layer structures explored their magnetic behavior through different models of Mn-incorporation in the crystal, evidenced as Mn spin S = 5/2, and provided an explanation for the low magnetization per Mn atom observed, signature of competing ferromagnetic and antiferromagnetic interactions between Mn2+ ions. Our studies provide insight to better understand and control the Mn incorporation in our samples to optimize their properties.

cond-mat.mtrl-sci↗

arXiv2024

Formation of Beta-Indium Selenide Layers Grown via Selenium Passivation of InP(111)B Substrate

Indium selenide, In2Se3, has recently attracted growing interest due to its novel properties, including room temperature ferroelectricity, outstanding photoresponsivity, and exotic in-plane ferroelectricity, which open up new regimes for next generation electronics. In2Se3 also provides the important advantage of tuning the electrical properties of ultra-thin layers with an external electrical and magnetic field, making it a potential platform to study novel two-dimensional physics. Yet, In2Se3 has many different polymorphs, and it has been challenging to synthesize single-phase material, especially using scalable growth methods, as needed for technological applications. In this paper, we use aberration-corrected scanning transmission electron microscopy to characterize the microstructure of twin-free single-phase ultra-thin layers of beta-In2Se3, prepared by a unique molecular beam epitaxy approach. We emphasize features of the In2Se3 layer and In2Se3/InP interface which provide evidence for understanding the growth mechanism of the single-phase In2Se3. This novel approach for forming high-quality twin-free single phase two-dimensional crystals on InP substrates is likely to be applicable to other technologically important substrates.

cond-mat.mtrl-sci↗

arXiv2023

Structural and magnetic properties of molecular beam epitaxy (MnSb2Te4)x(Sb2Te3)1-x topological materials with exceedingly high Curie temperature

Tuning magnetic properties of magnetic topological materials is of interest to realize elusive physical phenomena such as quantum anomalous hall effect (QAHE) at higher temperatures and design topological spintronic devices. However, current topological materials exhibit Curie temperature (TC) values far below room temperature. In recent years, significant progress has been made to control and optimize TC, particularly through defect engineering of these structures. Most recently we showed evidence of TC values up to 80K for (MnSb2Te4)x(Sb2Te3)1-x, where x is greater than or equal to 0.7 and less than or equal to 0.85, by controlling the compositions and Mn content in these structures. Here we show further enhancement of the TC, as high as 100K, by maintaining high Mn content and reducing the growth rate from 0.9 nm/min to 0.5 nm/min. Derivative curves reveal the presence of two TC components contributing to the overall value and propose TC1 and TC2 have distinct origins: excess Mn in SLs and Mn in Sb2-yMnyTe3QLs alloys, respectively. In pursuit of elucidating the mechanisms promoting higher Curie temperature values in this system, we show evidence of structural disorder where Mn is occupying not only Sb sites but also Te sites, providing evidence of significant excess Mn and a new crystal structure:(Mn1+ySb2-yTe4)x(Sb2-yMnyTe3)1-x. Our work shows progress in understanding how to control magnetic defects to enhance desired magnetic properties and the mechanism promoting these high TC in magnetic topological materials such as (Mn1+ySb2-yTe4)x(Sb2-yMnyTe3)1-x.

cond-mat.mtrl-sci↗

arXiv2023

Molecular Beam Epitaxy of Twin-Free Bi2Se3 and Sb2Te3 on In2Se3/InP(111)B Virtual Substrates

Three-dimensional topological insulators (3D-TIs) are a new generation of materials with insulating bulk and exotic metallic surface states that facilitate a wide variety of ground-breaking applications. However, utilization of the surface channels is often hampered by the presence of crystal defects, such as antisites, vacancies and twin domains. For terahertz device applications, twinning is shown to be highly deleterious. Previous attempts to reduce twins using technologically important InP(111) substrates have been promising, but have failed to completely suppress twin domains while preserving high structural quality. Here we report growth of twin-free molecular beam epitaxial Bi2Se3 and Sb2Te3 structures on ultra-thin In2Se3 layers formed by a novel selenium passivation technique during the oxide desorption of smooth, non-vicinal InP(111)B substrates, without the use of an indium source. The formation of un-twinned In2Se3 provides a favorable template to fully suppress twin domains in 3D-TIs, greatly broadening novel device applications in the terahertz regime.

cond-mat.mtrl-sci↗

arXiv2021

Compositional Control and Optimization of Molecular Beam Epitaxial Growth of (Sb2Te3)x(MnSb2Te4)y Magnetic Topological Insulators

Magnetic topological insulators such as MnBi2Te4 and MnSb2Te4 are promising hosts of novel physical phenomena such as quantum anomalous Hall effect and intrinsic axion insulator state, both potentially important for the implementation in topological spintronics and error-free quantum computing. In the bulk, the materials are antiferromagnetic but appropriate stacking with non-magnetic layers or excess Mn in the crystal lattice can induce a net ferromagnetic alignment. In this work we report the growth of (Sb2Te3)x(MnSb2Te4)y layers with varying Mn content by molecular beam epitaxy. The Mn flux fraction provided during growth controls the percent of MnSb2Te4 that is formed in the resulting layers by a self-assembly process. Highly crystalline layers with compositions varying between Sb2Te3 (y=0) and MnSb2Te4 (x=0) were obtained. The results show that Mn incorporates as a structural component to form MnSb2Te4, and as an impurity element both in Sb2Te3 and in MnSb2Te4. Two modifications of the growth conditions were implemented to enhance the incorporation of Mn as a structural element to form MnSb2Te4. Annealing of a thin portion of the layer at the beginning of growth (pre-anneal step), and increasing the growth temperature, both result in a larger percent of MnSb2Te4 for similar Mn flux fractions during growth. Samples having at least a few percent of MnSb2Te4 layers exhibit ferromagnetic behavior likely due to the excess Mn in the system which stabilizes on Sb sites as MnSb antisite defects.

cond-mat.mtrl-sci↗

arXiv2018

Self-assembled Bismuth Selenide (Bi2Se3) quantum dots grown by molecular beam epitaxy

We report the growth of self-assembled Bi2Se3 quantum dots (QDs) by molecular beam epitaxy on GaAs substrates using the droplet epitaxy technique. The QD formation occurs after anneal of Bismuth droplets under Selenium flux. Characterization by atomic force microscopy, scanning electron microscopy, X-ray diffraction, high-resolution transmission electron microscopy and X-ray reflectance spectroscopy is presented. The quantum dots are crystalline, with hexagonal shape, and have average dimensions of 12 nm height (12 quintuple layers) and 46 nm width, and a density of $8.5 \cdot 10^9 cm^{-2}$. This droplet growth technique provides a means to produce topological insulator QDs in a reproducible and controllable way, providing convenient access to a promising quantum material with singular spin properties.

cond-mat.mtrl-sci↗