The magnetocaloric effect (MCE), or the tendency of some materials to change temperature upon exposure to an external magnetic field, is the cornerstone of many eco-friendly technologies such as magnetic refrigeration. The compound AlFe2B2 is known to exhibit a large MCE at room temperature, and previous studies have shown that varying the stoichiometry, synthesis method, and treatment of this parent compound can further enhance the MCE by reducing impurities within the sample. Specifically, our team wanted to explore the effect of acid treatment and annealing on the magnetocaloric properties of this parent compound when doped with Si. To do this, we synthesized a system of Al0.85+xSi0.15Fe2B2 (x = 0.2, 0.4) alloys through conventional arc melting and drop-casting, annealed half of the samples at 900 degrees Celsius for one week, and further treated half of these annealed samples with diluted HCl for 20 minutes. We investigated the structural composition of the samples through analyzing X-ray diffraction (XRD) and scanning electron microscopy (SEM) data, then measured the magnetization of the samples at different temperatures and in different applied magnetic fields. Annealing was found to significantly reduce the presence of impurity phases and enhance the MCE, whereas acid treatment had little to no additional effect. Moving forward, it may be beneficial to explore the effects of annealing on a more diverse range of stoichiometrically-varied AlFe2B2 compounds or to adjust the acid treatment methodology in order to further enhance the MCE. This experience required an in-depth understanding of foundational crystallography concepts accompanied by an empirical aptitude for metallurgical synthesis and characterization, both of which are imperative for any career or further study in materials science.
Author(s): Kyra Stillwell, Physics Major
Advisor(s): Mahmud Khan, Department of Physics
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