Magnetocaloric effect: From materials research to refrigeration devices

The effect of adding high pressure as a control parameter in solids, liquids, and gases expands opportunities to observe unexpected novel phenomena and understand matter in extreme environments. This review on high pressure science highlights subjects ranging from quantum criticality to Earth science. State-of-the-art experimental methods at megabar pressures are also discussed. The proliferation of pressure-induced phases illustrate promising new directions for this field of research.

https://link.aps.org/accepted/10.1103/RevModPhys.90.015007

Solids, liquids, and gases under high pressure

Hierarchical CuCo2O4 nanobelts as a supercapacitor electrode with high areal and specific capacitance

Effect of cobalt substitution on structural, elastic, magnetic and optical properties of zinc ferrite nanoparticles

The hierarchical undoped and Cd-doped SnO2 nanostructures had been synthesized via a low-cost and environmentally friendly hydrothermal route. The morphology and structure of the as-prepared product were characterized by X-ray diffraction (XRD), field-emission electron microscopy (FESEM), and transmission electron microscopy (TEM). The images of field-emission electron microscopy and transmission electron microscopy showed that pure and Cd-doped SnO2 hierarchical architectures were built from one-dimensional nanorods. X-ray diffraction (XRD) of the doped samples revealed that Cd incorporation led to lattice deformation without destroying the original crystal structure. Gas sensors based on undoped and Cd-doped SnO2 nanorods were fabricated, and their gas sensing properties were tested for various gases. The 3.0 wt% Cd-doped SnO2 based sensor showed excellent selectivity toward H2S at the operating temperature 275 degrees C, giving a response of about 31-10 ppm, which was about 22 times higher than that of sensor based on pure SnO2. (C) 2013 Elsevier B.V. All rights reserved.

One-step synthesis and gas sensing properties of hierarchical Cd-doped SnO2 nanostructures

Nanoflake-structured NiO were synthesized by a microwave assisted method without the use of additives. The cubic phase of NiO nanoparticles with increasing crystalline nature for higher microwave power is ascertained by X-ray diffraction studies. Previous reports revealed that hexagonally structured β-Ni(OH)2 was completely transferred into the cubic phase of NiO around 350 °C, confirmed by using thermal analysis (TG/DTA). In our present work, the size and morphology of nanoparticles are ascertained from transmission electron microscopy (TEM) analysis. Flake-like morphology with uniform size, shape and less agglomerated structure formation is obtained for 900 and 600 W of microwave power used for the synthesis of NiO samples. The effect of microwave power used for the synthesis of NiO nanoflakes was analyzed by studying the magnetic and electrochemical behavior of NiO nanoflakes. Room temperature magnetic measurements revealed the small ferromagnetic nature of NiO nanoparticles. It was observed that the samples synthesized at higher microwave power exhibited divergence behavior below 300 K in FC and ZFC measurements, which results superparamagnetic behavior. An enhanced supercapacitor performance with higher specific capacitance values was determined for NiO nanoflake samples synthesized at 25600 W and 900 W of microwave power.

Influence of microwave power on the preparation of NiO nanoflakes for enhanced magnetic and supercapacitor applications.

Synthesis and calcinations effects on size analysis of Co3O4 nanospheres and their superparamagnetic behaviors

High aspect ratio La0.7Sr0.3MnO3 nanotube (NT) arrays have been synthesized using nitrates based sol-gel precursor by nanoporous anodized aluminum oxide template assisted method. Their phase purity and microstructures were analyzed by X-ray diffraction, scanning electron microscopy, and energy-dispersive x-ray spectroscopy. Magnetocaloric effect (MCE) of as prepared NTs was investigated by means of field dependence magnetization measurements. Significant magnetic entropy change, −△SM = 1.6 J/kg K, and the refrigerant capacitance, RC = 69 J/kg, were achieved near the transition temperature at 315 K for 5 T. For comparison, a bulk sample was also prepared using the same precursor solution which gives a value of −△SM = 4.2 J/kg K and a RC = 165 J/kg. Though the bulk sample exhibits higher △SM value, the NTs present an expanded temperature dependence of −△SM curves that spread over a broad temperature range and assured to be appropriate for active magnetic refrigeration. The diminutive MCE observed in manganite NTs is explained by the increased influence of surface sites of nanograins which affect the structural phase transition occurred by external magnetic field due to the coupling between magnetism and the lattice in manganese perovskites. Our report paves the way for further investigation in 1D manganite nanostructured materials towards applications in such magnetic refrigeration technology or even on hyperthermia/drug delivery.

Room temperature magnetocaloric effect and refrigerant capacitance in La0.7Sr0.3MnO3 nanotube arrays

On the role of cationic distribution in determining magnetic properties of Zn0.7-xNixMg0.2Cu0.1Fe2O4 nano ferrite

We have studied the magnetic entropy change of highly ordered La0.7Ca0.3MnO3 nanotube arrays synthesized by template assisted sol-gel method in temperatures ranging from 179 to 293 K and in magnetic fields up to 5 T. From the measurements of isothermal magnetization, we have calculated the maximum isothermal magnetic entropy change of −△SM = 1.9 J/kg K around the Curie temperature at 236 K for a field of 5 T. The nanotubes present lower magnetic entropy change compared with their bulk counterpart (−△SM = 4.8 J/kg K) which was prepared by the same sol-gel route. Such diminished magnetic entropy change observed in nanotubes is explained by the disordered magnetic states which are created on the surface sites of nanograins due to the larger surface to volume ratio. However, the nanotubes present an expanded magnetic transition that extends over a wide temperature range and suggest that such manganite nanotubes could be used for magnetic refrigeration with broad working temperature span.

M. Kumaresavanji

Papers

Influence of microwave power on the preparation of NiO nanoflakes for enhanced magnetic and supercapacitor applications.

Synthesis and calcinations effects on size analysis of Co3O4 nanospheres and their superparamagnetic behaviors

Room temperature magnetocaloric effect and refrigerant capacitance in La0.7Sr0.3MnO3 nanotube arrays

On the role of cationic distribution in determining magnetic properties of Zn0.7-xNixMg0.2Cu0.1Fe2O4 nano ferrite

Magnetocaloric effect in La0.7Ca0.3MnO3 nanotube arrays with broad working temperature span