The innovation engine for new materials

Sam Humphrey

Sam Humphrey


University of Oxford


Materials Science


Josh Bocarsly

Faculty Sponsor(s): 

Ram Seshadri

Faculty Sponsor's Department: 


Project Title: 

Structural modifications of MnB and AlFe2B2: next generation Earth-abundant magnetocalorics

Project Description: 

The magnetocaloric effect describes the change in temperature of a material when placed in a magnetic field. By cycling isothermal and adiabatic magnetizations and demagnetizations, this effect can be leveraged to build environmentally friendly and energy efficient refrigeration devices as an alternative to conventional vapour compression. Recent research has identified AlFe2B2 and MnB as two promising magnetocalorics for practical applications. These materials are attractive because they show a large entropy change upon magnetization and consist of Earth-abundant elements. To create a usable magnetic refrigerator, one must be able to reliably tune the properties of magnetocaloric material.  Here, we tune AlFe2B2 by substituting gallium for aluminium and MnB by substituting carbon for boron. The samples have been produced by three methods: assisted microwave reaction, liquid metal flux, and arc melting. Powder X-ray diffraction was used to characterize the changes in lattice parameters as the compositions were changed. Phase-pure MnB was prepared directly from high-temperature reaction of the elements, whereas AlFe2B2 had to be purified by rinsing with HCl. In both systems changes in magnetic transition temperature were observed as the composition was modified.