Mixed Magnetism for Refrigeration and Energy Conversion

TL;DR

This paper introduces a new form of mixed magnetism in hexagonal MnFe(P, Si) that enables tunable, efficient refrigeration and energy conversion by leveraging strong and weak magnetic interactions in layered structures.

Contribution

It reveals a novel coexistence of strong and weak magnetism in layered materials and demonstrates how to tune their properties for improved refrigeration and energy conversion.

Findings

Discovered coexistence of strong and weak magnetism in MnFe(P, Si) layers.

Showed that weak magnetism couples strongly with the lattice, enabling magnetocaloric effects.

Demonstrated tuning of magnetic properties to optimize operational temperature and reduce hysteresis.

Abstract

The efficient coupling between lattice degrees of freedom and spin degrees of freedom in magnetic materials can be used for refrigeration and energy conversion. This coupling is enhanced in materials exhibiting the giant magnetocaloric effect. First principle electronic structure calculations on hexagonal MnFe(P, Si) reveal a new form of magnetism: the coexistence of strong and weak magnetism in alternate atomic layers. The weak magnetism of Fe layers (disappearance of local magnetic moments at the Curie temperature) is responsible for a strong coupling with the crystal lattice while the strong magnetism in adjacent Mn-layers ensures Curie temperatures high enough to enable operation at and above room temperature. Varying the composition on these magnetic sublattices gives a handle to tune the working temperature and to achieve a strong reduction of the undesired thermal hysteresis. In this way we design novel materials based on abundantly available elements with properties matched to the requirements of an efficient refrigeration or energy-conversion cycle.