Influence of heat sintering on the physical properties of bulk La0.67Ca0.33MnO3 perovskite manganite: role of oxygen in tuning the magnetocaloric response

Pramod R. Nadig, M. S. Murari, Mamatha D. Daivajna

Research output: Contribution to journalArticlepeer-review

Abstract

The effect of heat treatments on bulk poly-crystalline La0.67Ca0.33MnO3 perovskite manganite is presented, to explore the possible enhancement in magnetocaloric performance. Samples were prepared via conventional solid-state reaction route with annealing and sintering at various temperatures. Detailed measurements of temperature-dependent and field-dependent magnetization were carried out to estimate the Curie point and order of magnetic transition. The increased sintering temperature results in a steep transition near the TC, and establishes the magnetic sensitivity as well as the active zone for substantial magnetocaloric performance, at about 168.2% for the LCM9 (sintered at 900 °C) sample. The cause for the significant improvement in the magnetic and magnetocaloric response is brought to light using detailed X-ray photoelectron spectroscopy (XPS) analysis, highlighting the role of oxygen in modifying the Mn3+/Mn4+ charge ratio. The maximum value of the isothermal magnetic entropy change for the optimized sample is found to be 6.4 J kg−1 K−1, achieved at 269 K, while temperature-averaged entropy change (TEC) values, TEC(ΔTH-C = 3 K) and TEC(ΔTH-C = 5 K), of 6 J kg−1 K−1 and 5.2 J kg−1 K−1, respectively, were obtained with a low magnetic field change of 20 kOe. The obtained isothermal entropy change at low field for the optimized La0.67Ca0.33MnO3 sample is higher than that of pure Gd and most oxide-based materials. The relative cooling power (RCP) value is around 93 J kg−1 (ΔH = 20 kOe). The order of the phase transition is examined with universal scaling; the scaled entropy change curves confirm the collapse onto a single curve for LCM9, asserting second-order character, whereas the breakdown of the curve with a dispersion relation (d) of 101.1% at Θ = −5 confirms the onset of intrinsic first-order nature in the case of the high-temperature-sintered samples. Calorimetry measurements show thermal hysteresis of 2.4 K and 7.1 K for LCM11 (sintered at 1100 °C) at ramp rates of 5 K min−1 and 10 K min−1, respectively, confirming the first-order nature of the magnetic transition.

Original languageEnglish
Pages (from-to)5237-5252
Number of pages16
JournalPhysical Chemistry Chemical Physics
Volume26
Issue number6
DOIs
Publication statusAccepted/In press - 2024

All Science Journal Classification (ASJC) codes

  • General Physics and Astronomy
  • Physical and Theoretical Chemistry

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