Effects of annealing on nanocrystalline GdVO 4 and its magnetocaloric properties
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Effects of annealing on nanocrystalline GdVO4 and its magnetocaloric properties Sung‑Myung Ryu1 · Chunghee Nam1,2 Received: 16 March 2020 / Accepted: 29 April 2020 © Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract The magnetocaloric effect (MCE) is an important phenomenon occurring in cryogenic cooling. Herein, a promising MCE material, GdVO4 nanopowder, was synthesized using a microwave-assisted hydrothermal method. The magnetic properties of the produced G dVO4 nanopowder were measured to investigate its MCE efficiency. The as-prepared G dVO4 nanopowder exhibited an antiferromagnetic–paramagnetic transition at 2.20 K, lower than that of bulk GdVO4 (2.50 K). The nanocrystalline GdVO4 showed weak antiferromagnetism due to size effects, where the broken symmetry of the surfaces resulted in a low crystalline anisotropy. However, the GdVO4 nanopowder after annealing at 900 °C showed an increased TN of 2.50 K due to aggregation and the resulting suppression of the size effects. Based on the Maxwell relation, the magnetic entropy change was obtained and compared with that of bulk GdVO4. Although the change in the maximum magnetic entropy was reduced for the nanocrystalline GdVO4 compared to that of bulk GdVO4, the absence of hysteresis loss in the nanocrystalline GdVO4 is important for high-efficiency magnetocaloric materials to be used in hydrogen liquefaction applications. Keywords Microwave hydrothermal method · GdVO4 · Magnetocaloric material · Nanocrystalline oxide
1 Introduction Vapor-compression refrigeration is the most commonly used method for cooling. However, a significant limitation of the vapor-compression refrigeration technology is its negative environmental impacts, as the chemicals used in the system can damage the ozone layer and exacerbate global warming [1, 2]. Recently, proposals for novel cooling technologies to replace the existing methods have included thermoelectric cooling, thermoacoustic refrigeration and magnetic refrigeration [3–8]. Among them, the magnetic refrigeration technology is based on the magnetocaloric effect (MCE) [3–8]. The MCE is a magneto-thermodynamic phenomenon in which the temperature of a material changes when it is exposed to changing magnetic fields [6]. The MCE magnitude can be quantified by the temperature change that occurs when the magnetic field changes in an adiabatic process or * Chunghee Nam [email protected] 1
Department of Photonics and Sensors, Hannam University, Daejeon 34430, Republic of Korea
Department of Electrical & Electronic Engineering, Hannam University, Daejeon 34430, Republic of Korea
2
via the magnetic entropy change when the magnetic field changes during an isothermal process [6]. The MCE can be applied to cooling technology, especially in cryogenic applications for space science and liquefaction of hydrogen and other fuel gases [4]. Recently, hydrogen has attracted significant attention as an alternative energy source to replace fossil fuels that cause greenhouse gas emissions when burned. To efficient
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