Abstract
The magnetic and magnetocaloric effects of potassium-substituted La0.8−xKxBa0.05Sr0.15MnO3 (0 ≤ x ≤ 0.20) manganite were explored. The samples in polycrystalline form were synthesized by the sol–gel method, with a final sintering temperature of 1100 °C. Powder X-ray diffraction (XRD) patterns refined by Rietveld refinement show that all samples crystallized in rhombohedral structure with R-3c space group. The unit cell volume of the samples decreases with increasing potassium concentration. In addition, small changes in average bond length and bond angle are also observed in the samples. Scanning electron microscope (SEM) images reveal that the largest average grain size was observed for x = 0.10. Field-cooled (FC) magnetization measurements show that the Curie temperature ( T C ) of the samples increases from 320 K for x = 0 to 360 K for x = 0.2. The largest magnetocaloric (MCE) effect, which is represented by maximum magnetic entropy change (− Δ S M , M A X ), reaches its greatest value for the x = 0.10 sample. The monotonous increase in T C suggests that TC is mainly governed by the ferromagnetic coupling between Mn ions induced by the changes on average bond length and bond angle. The obtained − Δ S M , M A X value suggests that MCE property is more sensitive to Zener theory of double exchange, which is strongly related to the Mn3+/Mn4+ ratio of the samples.
Highlights
The demand for alternative refrigerant technology has significantly increased in the last decade.This is due to the use of harmful substances in conventional vapor compression technology, which is involved in the ozone depletion phenomenon
Magnetic refrigerant technology uses the principle of the magnetocaloric effect (MCE) property of ferromagnetic materials [1]
MCE property of ferromagnetic materials can be represented by two expressions which are magnetic entropy change (∆SM ) and adiabatic temperature change (∆Tad ) [2]
Summary
The demand for alternative refrigerant technology has significantly increased in the last decade This is due to the use of harmful substances in conventional vapor compression technology, which is involved in the ozone depletion phenomenon. MCE can be defined as the ability of ferromagnetic materials to change its temperature in the presence of an external magnetic field [1] This makes MCE an environmentally friendly technology and, can contribute to limit the use of harmful substances in the refrigerant system. MCE property of ferromagnetic materials can be represented by two expressions which are magnetic entropy change (∆SM ) and adiabatic temperature change (∆Tad ) [2] These two expressions arise from two different methods, which were used to observe the magnitude of the MCE property [3]. Of these two expressions, ∆SM is usually the most used expression in research on the MCE property, due to the simplicity of the experimental set up
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