abstract
Manganites with the formula La1-xCaxMnO3 for 0.2 < x < 0.5 undergo a magnetic field driven transition from a paramagnetic to ferromagnetic state, which is accompanied by changes in the lattice and electronic structure. An isotropic expansion of the La0.75Ca0.25MnO3 cell at the phase transition has been observed experimentally. It is expected that there will be a large entropy change at the transition due to its first order nature. Doped lanthanum manganite (LMO) is therefore of interest as the active component in a magnetocaloric cooling device. However, the maximum obtained value for the entropy change in Ca-doped manganites merely reaches a moderate value in the field of a permanent magnet. The present theoretical work aims to shed light on this discrepancy. A combination of finite temperature statistical mechanics and first principles theory is applied to determine individual contributions to the total entropy change of the system by treating the electronic, lattice and magnetic components independently. Hybrid-exchange density functional (B3LYP) calculations and Monte Carlo simulations are performed for La0.75Ca0.25MnO3. Through the analysis of individual entropy contributions, it is found that the electronic and lattice entropy changes oppose the magnetic entropy change. The results highlighted in the present work demonstrate how the electronic and vibrational entropy contributions can have a deleterious effect on the total entropy change and thus the potential cooling power of doped LMO in a magnetocaloric device.
keywords
ENTROPY CHANGE; SINGLE-CRYSTAL; TEMPERATURE; MAGNETORESISTANCE; LA0.7CA0.3MNO3; REFRIGERATION; LA1-XCAXMNO3
subject category
Physics
authors
Korotana, RK; Mallia, G; Fortunato, NM; Amaral, JS; Gercsi, Z; Harrison, NM
our authors
João Cunha de Sequeira Amaral
Assistant Researcher
Nuno Fortunato
Research FellowshipGroups
G2 - Photonic, Electronic and Magnetic Materials
G6 - Virtual Materials and Artificial Intelligence
acknowledgements
We thank L F Cohen, K G Sandeman and J A Turcaud of The Blackett Laboratory, Imperial College London for useful discussions. The EPSRC Grant (EP/G060940/1) on Nanostructured Functional Materials for Energy Efficient Refrigeration, Energy Harvesting and Production of Hydrogen from Water is gratefully acknowledged. This work made use of the high performance computing facilities of Imperial College London and-via membership of the UK's HPC Materials Chemistry Consortium funded by EPSRC (EP/L000202)-of ARCHER, the UK's national high-performance computing service, which is provided by UoE HPCx Ltd. at the University of Edinburgh, Cray Inc. and NAG Ltd., and funded by the Office of Science and Technology through EPSRC. This work was developed within the scope of the project CICECO-Aveiro Institute of Materials, POCI-01-0145-FEDER-007679 (FCT Ref. UID/CTM/50011/2013), financed by national funds through the FCT/MEC and when appropriate co-financed by FEDER under the PT2020 Partnership Agreement. JSA acknowledges FCT SFRH/BPD/111270/2015 grant. ZG acknowledges the financial support from a Marie Curie Intra European Fellowship within the 7th European Community Framework Programme.