Investigation of magnetic properties of fe2mnp-based materials for refrigeration using density functional theory

Abstract

Increased campaign against environmental pollution and public awareness concerning global warming and food security has necessitated the efforts for reduction of emission of gases that adversely affect environment and deplete ozone layer. These gases include carbon (IV) oxide and chlorofluorocarbons, especially those emitted by compressed fluid refrigerators that are currently on the market. Alternative technologies are required to minimize or eliminate the emission of these harmful gases. Magnetocaloric effect (MCE), is a phenomenon related to the application and removal of varying magnetic field, which in turn shows changes in temperatures among selected magnetic materials. This effect forms the basis of a new alternative technology, magnetic refrigeration, a superior technology compared to compressed fluid refrigeration. However, many of the magnetic materials have been found to be structurally unstable, toxic and inefficient in terms of power consumption, hence not suitable to be magnetic refrigerants. Therefore, this study investigated the magnetic properties of stable iron-based compounds (Fe2MnP-A (A= indium In, selenium Se, and tin Sn) under thermal and magnetic cycles as viable magnetic refrigerants. The properties investigated included absolute magnetization, total magnetization and magnetic phase transition. Parent compound had A as silicon which was later substituted with atoms of Se, Sn and In hence viable refrigerant which showed large MCE was modelled as the magnetic refrigerant. The compound has been shown to exhibit a magnetocaloric effect due to its magnetic nature and hence can be used as a magnetic refrigerant. The study reported was carried out using Density Functional Theory (DFT) as the modelling and simulation method of the material. This theory is a ground state method which aims at obtaining a structurally stable system. MCE phenomenon on structurally stable compound (Fe2MnP-A (A= In, Se, and Sn) modelled by DFT was determined using first principle calculations. When Si was used at the A site, instability along the magnetic phase transition was observed. When indium, Se and Sn replaced silicon in FeMnPSi, it was observed that there was an effect in both total and absolute magnetization. Se and Sn showed a reduction in magnetic moment whereas In showed promising results by an increase in magnetic moment. The electronic band structure results indicated that they were all studied materials were metals. Antiferromagnetic states showed no net magnetic moments as the spin-polarized graph resulted in perfect symmetry of spin-up projected density of states (PDOS) and spin-down PDOS. From the thermo_pw calculations, it was realized that FeMnP0.67 In0.33 is the best candidate for magnetic refrigeration among the studied compounds.