Developing environmentally friendly refrigeration technologies using MnFePGe magnetocaloric materials

Since traditional gases, such as Freon, chlorofluorocarbons and hydrofluorocarbons, and their mechanical compression can exacerbate the greenhouse effect, researchers have been focused on new refrigeration technologies such as magnetic refrigeration based on the magnetocaloric effect. Recently, MnFePGe magnetocaloric materials have been widely studied as promising candidates for magnetic refrigeration materials.

Liu et al. established the relationship between covalent bond length, electronic density, and the important magnetocaloric properties of the MnFePGeM series of compounds, where M is a metallic or nonmetallic doped element.

“Our results provide an understanding of how to control the properties, enabling effective ways to tune the composition of functional materials to tailor physical properties for optimal performance,” said author Danmin Liu.

For the 54 samples investigated, the researchers found the increased length of coplanar Fe/Mn-Ge/P bond and Mn-P bond is correlated with the net moment and exchange interaction, and thus, the Curie temperature of the compounds or the temperature above which certain materials lose their permanent magnetic properties. On the other hand, they also found that the important determining factor for the thermal hysteresis—the condition where thermal history determines the behavior and properties of the system—is the difference of the coplanar bond length, rather than its absolute value.

New technologies based on the magnetocaloric effect have numerous environmentally friendly advantages, including high energy efficiency, long life, high reliability, easy maintenance, and straightforward recycling at end-of-life.

“This research provides some ideas for finding the relationship between the microstructure, composition and the physical properties in order to understand the nature of first order transition,” said Liu. “This procedure could be used for the research of many functional materials especially for first order transition materials.”

Source: “The correlation between the covalent bonds and magnetocaloricproperties of the Mn_2-xFe_xP_yGe_1-yM_z compounds,” by H. R. Zhang, D. M. Liu, Z. L. Zhang, S. B. Wang, M. Yue, Q. Z. Huang, and J. W. Lynn, Journal of Applied Physics (2021). The article can be accessed at https://doi.org/10.1063/5.0056190 .