Structural and Magnetic Characterization of Co50Mn30InxSn(20-x) (x= 0, 5, 10, 15, and 20) Samples for Magnetocaloric Effect

Master's Thesis from the year 2010 in the subject Chemistry - Materials Chemistry, grade: A, University of the Basque Country (University of Basque country(UPV/EHU)), course: Material science - Masters in Nanoscience, language: English, abstract: Nowadays magnetic refrigeration which is based on the Magnetocaloric Effect (MCE) is one of the more relevant topics in the scientific research owing to its very important technological applications, which derive from the attempts made to replace the gas refrigerating technology involving, among other transcendental aspects, a low impact in the environment and an expected higher energetic efficiency. Furthermore, new and improved magnetocaloric materials are one of the cornerstones in the development of room temperature magnetic refrigeration. This master's work has mainly been concerned in a development of a deep and systematic study of magnetic and magnetocaloric properties of ribbon samples of Heusler alloy family of materials with compositions susceptible of exhibiting MCE, For this purpose, we have focused on ribbons of chemical composition Co50Mn30InxSn (20-x) (x= 0, 5, 10, 15, and 20).
Co50Mn30InxSn (20-x) Heusler alloys were prepared by arc melting admixtures of the pure elements in the desired quantities under argon atmosphere. The ribbons have been prepared by melt spinning technique. X-ray characterization proved the face centered cubic austenite Heusler alloy phase (211) crystal structural with lattice constant a = 0.5947 nm of as cast and annealed ribbons. Differential Scanning Calorimetry was used to find the temperatures of the recrystallization phase transitions. Magnetization was measured for as-cast and annealed samples. Both Curie temperatures and coercivity were found to be lower in the as-cast samples than in the glass tube annealed ones. Monotonic decreasing of the Curie temperature was observed in the series with the growth of the content.
MCE has been evaluated for one of the samples (x = 15) and a maximum value of entropy change is 2.37 JKg-1K-1 have been found, which is the same order of magnitude that reported of Gd alloys.