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Comparative study of magnetocaloric properties for Gd3+ compounds with different frustrated lattice geometries

Accepted version
Peer-reviewed

Type

Article

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Authors

Koskelo, EliseAnne 
Mukherjee, Paromita 
Liu, Cheng 
Sackville-Hamilton, Alice 

Abstract

As materials with suppressed ordering temperatures and enhanced ground state entropies, frustrated magnetic oxides are ideal candidates for cryogenic magnetocaloric refrigeration. While previous materials design has focused on tuning the magnetic moments, their interactions, and density of moments on the lattice, there has been relatively little attention to frustrated lattices. Prior theoretical work has shown that the magnetocaloric cooling rate at the saturation field is proportional to a macroscopic number of soft mode excitations that arise due to the classical ground state degeneracy. The number of these modes is directly determined by the geometry of the frustrated lattice. For corner-sharing geometries, the pyrochlore has 50% more modes than the garnet and kagome lattices, whereas the edge-sharing fcc has only a subextensive number of soft modes. Here, we study the role of soft modes in the magnetocaloric effect of four large-spin Gd3+ (L = 0, J = S = 7/2) Heisenberg antiferromagnets on a kagome, garnet, pyrochlore, and fcc lattice down to T = 2 K. By comparing measurements of the magnetic entropy change ∆Sm of these materials at fields up to 9 T with predictions using mean-field theory and Monte Carlo simulations, we are able to understand the relative importance of spin correlations and quantization effects. We observe that tuning the value of the nearest neighbor coupling has a more significant contribution to the magnetocaloric entropy change in the liquid-He cooling regime (2-20 K), rather than tuning the number of soft mode excitations. Our results provide a base for future refrigerant-material design in terms of dimensionality, degree of magnetic frustration, and lattice geometry.

Description

Keywords

4902 Mathematical Physics, 49 Mathematical Sciences, 34 Chemical Sciences

Journal Title

PRX Energy

Conference Name

Journal ISSN

2768-5608
2768-5608

Volume Title

Publisher

American Physical Society
Sponsorship
Engineering and Physical Sciences Research Council (EP/P007767/1)
EPSRC (EP/T028580/1)
Engineering and Physical Sciences Research Council (EP/P034616/1)
EPSRC (EP/V062654/1)
EPSRC grants: EP/P034616/1, EP/V062654/1, EP/T028580/1, EP/M0005/24/1 Winton Programme for the Physics of Sustainability. Churchill Scholarship from the Winston Churchill Foundation of the United States. Agence Nationale de la Recherche, France, Grant No. ANR-18-CE05-0023.
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