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Author Phan, The-Long ♦ Jung, C. U. ♦ Lee, B. W. ♦ Ho, T. A. ♦ Manh, T. V. ♦ Dang, N. T. ♦ Thanh, T. D.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSICS ♦ COMPARATIVE EVALUATIONS ♦ DOPED MATERIALS ♦ ENTROPY ♦ MAGNETIC FIELDS ♦ MAGNETIC PROPERTIES ♦ MANGANESE IONS ♦ MEAN-FIELD THEORY ♦ ORTHORHOMBIC LATTICES ♦ PARAMAGNETISM ♦ PHASE TRANSFORMATIONS ♦ REFRIGERANTS ♦ REFRIGERATION ♦ TRANSITION TEMPERATURE
Abstract We prepared orthorhombic La{sub 0.7−x}Y{sub x}Ca{sub 0.3}MnO{sub 3} samples (x = 0, 0.04, 0.06, and 0.08) by conventional solid-state reaction and then studied their magnetic properties and magnetocaloric (MC) effect based on magnetization versus temperature and magnetic-field measurements, M(T, H). The experimental results revealed that an x increase in La{sub 0.7−x}Y{sub x}Ca{sub 0.3}MnO{sub 3} reduced the ferromagnetic-paramagnetic transition temperature (T{sub C}) from 260 K (for x = 0) to ∼126 K (for x = 0.08). Around the T{sub C}, maximum magnetic-entropy changes for a magnetic-field variation interval H = 50 kOe are about 10.7, 8.5, 7.4, and 5.8 J·kg{sup −1}·K{sup −1} for x = 0, 0.04, 0.06, and 0.08, respectively, corresponding to refrigerant capacities RC = 250–280 J·kg{sup −1}. These values are comparable to those of some conventional MC materials, revealing the applicability of La{sub 0.7−x}Y{sub x}Ca{sub 0.3}MnO{sub 3} in magnetic refrigeration. Using the Arrott method and scaling hypothesis as analyzing high-field M(H, T) data, and the universal-curve construction of the magnetic entropy change, we found a magnetic-phase separation. While the samples x = 0−0.06 exhibit a first-order magnetic phase transition, x = 0.08 exhibits the crossover of the first-to-second-order phase transformation (with its critical-exponent values close to those expected for the tricritical mean-field theory) and has the presence of ferromagnetic clusters even above the T{sub C}. Such the variations in the magnetism and MC effect are related to the changes in structural parameters caused by the Y substitution for La because Y doping does not change the concentration ratio of Mn{sup 3+}/Mn{sup 4+}.
ISSN 00218979
Educational Use Research
Learning Resource Type Article
Publisher Date 2015-10-14
Publisher Place United States
Journal Journal of Applied Physics
Volume Number 118
Issue Number 14


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