Elsevier

Journal of Alloys and Compounds

Volume 735, 25 February 2018, Pages 773-776
Journal of Alloys and Compounds

Large reversible normal and inverse magneto-caloric effects in the RE2BaCuO5 (RE = Dy and Er) compounds

https://doi.org/10.1016/j.jallcom.2017.11.146Get rights and content

Highlights

  • Magnetic properties and magneto-caloric effect (MCE) in RE2BaCu2O5 were studied.

  • Antiferromagnetic ordering at 11.4 and 7.8 K for RE = Dy and Er, respectively.

  • Field-induced metamagnetic transition below TN for both compounds.

  • Inverse MCE under low field change at low temperatures for both compounds.

  • Large normal reversible MCE under high field changes for both compounds.

Abstract

The magneto-caloric effect (MCE) in the polycrystalline rare-earth cuprates Dy2BaCuO5 and Er2BaCuO5 has been researched. An inverse MCE under low magnetic field changes (ΔH) and at low temperatures together with a large normal reversible MCE under high ΔH was observed for the both compounds. These behaviours are corresponding to the fact of AFM (antiferromagnetic) ground state and the field-induced metamagnetic transition (first order) from AFM to FM (ferromagnetic) state in Dy2BaCuO5 and Er2BaCuO5 compounds. For the ΔH of 0–7 T, the values of −ΔSMmax (maximum magnetic entropy change), RCP (relative cooling power) and RC (refrigerant capacity) are found to be 8.3 J/kg K, 204 J/kg and 153 J/kg for Dy2BaCuO5, and to be 9.6 J/kg K, 230 J/kg and 176 J/kg for Er2BaCuO5, respectively.

Introduction

Magnetic refrigeration (MR) based on exploiting the magneto-caloric effect (MCE) is taken as a more reduced environment impact technique compared with traditional well-used gas expansion/compression refrigeration, since it does not involve ozone-depleting or greenhouse related gases [1], [2], [3], [4]. MCE is an intrinsic magneto-thermal response of all the magnetic solids and it arises from the correlations between the magnetic sub-lattice and the external magnetic fields. It can be usually manifested as ΔSM (isothermal magnetic part of entropy change) and ΔTad (adiabatic temperature change). The search for potential working substances with large/giant MCE is essential for the future important requirement of MR technology. Consequently, the magnetism and magneto-caloric properties in many RE (rare earth) - based alloys and oxides have been reported recently, and some of them are reported to have excellent magneto-caloric properties [1], [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13].

The rare-earth (RE) “green phase” cuprates with the general formula of RE2BaCuO5 (also named as RE-211 phase) for RE = Y, Sm-Lu are known as attendant components in famous REBa2Cu3O7-δ (RE-123 phase) high-Tc superconductors [14], [15], [16], [17], [18], [19], [20]. These RE-211 compounds are crystallized in the orthorhombic crystal structure belonging to Pbnm space group which has a single Cu site and two RE sites of equal occurrence. The critical current densities (Jc) of RE-123 superconductors can be effectively improved by adding the non-superconducting RE-211 second phase particle [16], [17]. Up to the present, there is no report related to the MCE of these green cuprates. Therefore, the magneto-caloric properties together with the magnetic transition in Dy2BaCuO5 and Er2BaCuO5 were investigated. A field-induced metamagnetic transition (AFM state to FM state) together with interesting magneto-caloric properties was observed in both green compounds.

Section snippets

Experimental details

Polycrystalline samples of Dy2BaCuO5 and Er2BaCuO5 were synthesized by a sol-gel method. High-purity Dysprosium acetates, Erbium acetates, Barium hydroxide, and Copper acetates were used as starting materials and dissolved in deionized water. Make sure a 2:1:1 stoichiometry of RE, Ba, and Cu ions in the solutions. Ethylene glycol and citric acid are added as cross-linking and chelating agent. The pH value of the solution was adjusted to 6.6 by ammonium hydroxide. The sol was obtained with

Results and discussion

The room temperature XRD patterns for Dy2BaCuO5 and Er2BaCuO5 compounds together with Rietveld refinement are given in Fig. 1. The corresponding Miller indexes are marked. Based on the refinement results, we obtained the reliability parameters of Rwp = 9.9% and Rexp = 8.3% for Dy2BaCuO5, and of Rwp = 9.6% and Rexp = 6.7% for Er2BaCuO5, respectively. The Dy2BaCuO5 and Er2BaCuO5 are confirmed to be single-phase orthorhombic crystal structure with Pnma space group. The values of a, b, and c

Conclusions

In summary, two single phased cuprates of Dy2BaCuO5 and Er2BaCuO5 (RE-211 phase) were synthesized by sol-gel method and their magnetism and magneto-caloric properties were reported. The RE2BaCuO5 compounds undergo a PM to AFM transition together with a metamagnetic transition (field-induced) from AFM to FM with the increases of H. An inverse together with a normal large reversible MCE for RE2BaCuO5 are observed. The inverse MCE is corresponding to the fact of AFM state (under low magnetic

Acknowledgements

This work was supported by the National Natural Science Foundation of China (Grant Nos. 51671048, 11374081 and 11574066).

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