Development of Software Tools and Experimental in Situ Electron Spin Resonance for Characterizing the Magnetic and Electrocatalytic Properties of Transition Metal Chalcogenide Crystals
Studying the magnetic properties and crystal defects of transition metal chalcogenide crystals is of paramount importance for utilizing them for next generation spintronics devices and hydrogen evolution reaction catalysts. Hydrothermally grown transition metal chalcogenide nanocrystals (MoS2, Ru2S3, Rh2S3, Co2S8) were chosen as catalysts for the hydrogen evolution reaction due to their low dimensionality and previous utilization as catalysts for hydrodesulfurization. The relationship between crystal defect sites and catalytic activity must be discerned to maximize the efficiency of hydrogen production during the hydrogen evolution reaction. ESR spectroscopy was utilized as a spin sensitive technique to study the defects and local changes to the composition and electronic structure of the crystals ex situ, before and after the reaction. Additionally, an in situ ESR cell was created to monitor the ESR response during the hydrogen evolution reaction. This new in situ experimental set up allowed us to sensitively track voltage-dependent changes to MoS2.To further probe the magnetic properties of transition metal chalcogenide crystals, computational tools were developed to study the universality classes, spin dimensionality, spin correlations, and effective spatial dimensionality of magnetic interactions. Continuous phase transitions may be described in terms of critical exponents, critical amplitudes, and the critical transition temperature, which can lead to the determination of the magnetic properties mentioned above. Despite the intrinsic value, experimentally extracting the critical exponents and critical amplitudes from isothermal magnetization measurements is a time-consuming, monotonous task that is prone to error. These errors often result in the incorrect assignment of critical exponents, and contradictions in published literature often exist for the same compound. To address these issues, a program has been developed to automate and simplify the task of calculating the critical parameters. The program calculates the critical exponents using self-consistent methods, including the modified and traditional asymptotic analyses, based on the Kouvel Fisher method, Modified Arrott Plot method, and generalized magnetic equation of state (scaling analysis). For the first time, a computational routine has been integrated to calculate explicit numerical solutions for the critical exponents with isotropic, long-range interactions, resulting in excellent agreement between theoretical and experimental calculations of the spin correlations. These tools can be applied to a broad range of magnetic material systems. Using these computational tools, the critical parameters and spin dimensionalities have been calculated for Mn3Si2Te6 and Fe2.64GeTe2; our calculations were found to agree with previously published results. To further demonstrate the program’s abilities, the critical parameters of proton irradiated Mn3Si2Te6 were calculated. Trends in the spin correlations of the irradiated samples allowed us to gain incredible insight on the nature of spin interactions as a function of proton irradiation.
Condensed matter physics|Nanoscience|Materials science
Delgado, Jose Armando, "Development of Software Tools and Experimental in Situ Electron Spin Resonance for Characterizing the Magnetic and Electrocatalytic Properties of Transition Metal Chalcogenide Crystals" (2020). ETD Collection for University of Texas, El Paso. AAI28262077.