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Bulk and Thin Film Synthesis of Compositionally Variant Entropy-stabilized Oxides
Published on: May 29, 2018
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Unveiling the Hidden Entropy in ZnFe2O4
Miguel Angel Cobos1, Antonio Hernando1,2,3,4, José Francisco Marco5
1Instituto de Magnetismo Aplicado (UCM-ADIF), CSIC, 28260 Las Rozas, Spain.
Materials (Basel, Switzerland)
|February 15, 2022
Summary
Slight deviations from ideal structure in ZnFe2O4 create local ferrimagnetic regions alongside antiferromagnetic and disordered phases. This structural change explains the observed "hidden" entropy in magnetic materials.
Area of Science:
- Materials Science
- Solid State Physics
- Magnetism
Background:
- Normal ZnFe2O4 exhibits antiferromagnetic (AFM) transitions with disordered spins and "hidden" entropy at zero or near-zero inversion degrees (δ).
- The inversion degree (δ) significantly influences magnetic properties, prompting investigation into minor deviations from ideal structures.
Purpose of the Study:
- To investigate the effect of small inversion degrees (δ = 0.05 and 0.27) on the magnetic properties of ZnFe2O4.
- To understand the coexistence and behavior of different magnetic phases under applied fields.
Main Methods:
- Calorimetry at varying applied magnetic fields.
- Mössbauer spectroscopy.
Main Results:
- A small inversion degree (δ = 0.05) affects ~40% of unit cells, leading to locally ferrimagnetic (FiM) regions coexisting with AFM and spin-disordered regions.
- Spin disorder diminishes under a 1 T applied field.
- Entropy and hyperfine measurements indicate roughly equal volume fractions (~1/3 each) for AFM, FiM, and spin-disordered phases.
Conclusions:
- The "hidden" entropy in ZnFe2O4 is attributed to zero-point entropy arising from spin frustrations at the interfaces between AFM and FiM phases.
- These frustrations occur due to non-ideal inversion degrees (δ ≠ 0).
- The coexistence of multiple magnetic phases is a key feature in slightly disordered ZnFe2O4.
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