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Published on: October 5, 2013
The magnetocaloric effect at the first-order magneto-elastic phase transition
1Istituto Nazionale di Ricerca Metrologica, Torino, Italy. v.basso@inrim.it
Summary
This study reveals how structural changes amplify the magnetocaloric effect, leading to a giant magnetocaloric effect when magnetic and structural entropy changes align. This phenomenon is controlled by a key parameter, zeta.
Area of Science:
- Condensed Matter Physics
- Thermodynamics
- Materials Science
Background:
- The magnetocaloric effect (MCE) is crucial for magnetic refrigeration.
- Understanding MCE at phase transitions is key to optimizing performance.
- Magneto-elastic coupling can significantly influence phase transitions.
Purpose of the Study:
- To investigate the magnetocaloric effect during first-order magneto-elastic phase transitions.
- To analyze the interplay between magnetic and structural contributions to entropy change.
- To identify conditions for achieving a giant magnetocaloric effect.
Main Methods:
- Development and application of a thermodynamic model.
- Analysis of entropy change (Δs) at the transition temperature.
- Investigation of the role of the dimensionless parameter zeta (ζ).
Main Results:
- Entropy change (Δs) is a sum of magnetic and structural contributions.
- The parameter ζ, dependent on exchange force steepness (β) and thermal expansion (α(p)), governs the structural contribution.
- A giant MCE occurs for ζ < 0 due to aligned magnetic and structural entropy changes.
- For 0 < ζ < 1, contributions partially cancel.
- For ζ > 1, structural entropy dominates, driving a paramagnetic to ferromagnetic transition upon heating.
Conclusions:
- The structural contribution to entropy change is critical for MCE magnitude.
- A giant MCE is achievable under specific magneto-elastic coupling conditions (ζ < 0).
- The thermodynamic model provides a framework for predicting and designing materials with enhanced MCE.
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