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- 검색키워드
- 저자 : Dimitar N. Petrov (검색결과 2 건)
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Enhanced magnetocaloric effect in Eu-doped La0.7Ca0.3MnO3 compounds
N.T. Dang,D.P. Kozlenko,Kim Gareoung,손원혁,이종수,Dimitar N. Petrov,T. V. Manh,Phan The Long 한국물리학회 2020 Current Applied Physics Vol.20 No.6
Orthorhombic La0.7-xEuxCa0.3MnO3 samples (x = 0.04–0.12) with apparent density of ρ = 3.9–4.1 g/cm3 prepared by solid-state reactions have been studied. The analysis of temperature-dependent magnetization for an applied field H = 500 Oe indicated a decrease of the Curie temperature (TC) from about 225 K for x = 0.04 through 189 K for x = 0.08–146 K for x = 0.12. The magnetocaloric (MC) study upon analyzing M(H, T) data has revealed that the magnetic entropy change around TC reaches the maximum (|ΔSmax|), which is dependent on both x and H. For an applied field interval of ΔH = 60 kOe, |ΔSmax| values are about 5.88, 4.93, and 4.71 J/ kg⋅K for x = 0.04, 0.08, and 0.12, respectively. Though |ΔSmax| decreases with increasing x, relative cooling power (RCP) increases remarkably from 383 J/kg for x = 0.04 to about 428 J/kg for x = 0.08 and 0.12. This is related to the widening of the ferromagnetic-paramagnetic transition region when x increases. Particularly, if combining two compounds with x = 0.04 and 0.08 (or 0.12) as refrigerant blocks for MC applications, a cooling device can work in a large temperature range of 145–270 K, corresponding to RCP ≈ 640 J/kg for H = 60 kOe. M(H) analyses around TC have proved x = 0.04 exhibiting the mixture of first- and second-order phase transitions while x = 0.08 and 0.12 exhibit a second-order nature. The obtained results show potential applications of Eu-doped La0.7Ca0.3MnO3 materials for magnetic refrigeration below room temperature.
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Short-range magnetic order in La1-xBaxCoO3 cobaltites
Phan The Long,Dimitar N. Petrov,J. Ćwikd,N.T. Dang,Viet Dongquoc 한국물리학회 2018 Current Applied Physics Vol.18 No.11
Magnetization versus temperature and magnetic-field measurements, M(T, Ha), have been carried out to study the magnetic and critical properties of polycrystalline La1-xBaxCoO3 (x=0.3 and 0.5) cobaltites. These compounds with the density of ∼6.2 g/cm3 crystallized in the R3c rhombohedral and Pm3m cubic structures, respectively. With an applied field Ha=200 Oe, M(T) data have revealed that the samples with x=0.3 and 0.5 exhibit the ferromagnetic-paramagnetic (FM-PM) phase transition at the Curie temperature points TC=202 and 157 K, respectively. At 4.2 K, the saturation magnetization (Msat) decreases from 35.9 emu/g for x=0.3–26.1 emu/g for x=0.5. Particularly, the critical-behavior analyses in the vicinity of TC reveal all samples undergoing a second-order phase transition, with critical exponent values (β=0.328 and γ=1.251 for x=0.3, and β=0.331 and γ=1.246 for x=0.5) close to those expected for the 3D Ising model. This proves short-range magnetic order existing in La1-xBaxCoO3. We believe that magnetic inhomogeneities due to the mixture of holerich FM regions (confined in the trivalent-cobalt hole-poor anti-FM matrix) and uniaxial anisotropy prevent longrange order in La1-xBaxCoO3.
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