Wen-Zhe Nan

Influence of Sn-doping on Magnetocaloric Properties of La0.7Ca0.3Mn1−xSnxO3(x = 0.0, x = 0.02 and x = 0.04) Compounds

Modern technology for refrigerators and coolers is based on the chemical gas Chlorofluorocarbon (CFC) compression method that is indicative of a high consumption of electricity. The CFC is also understood as a reason for global warming. One of the solutions to this issue is magnetic refrigeration technology, which is environmentally friendly because it does not use any hazardous chemicals or ozone depleting/greenhouse gases. Magnetic refrigeration technology is based on the magnetocaloric effect of magnetic refrigerant materials. Exploring the magnetocaloric effect of magnetic refrigerant materials is important because these contain many of the physical properties needed for magnetic refrigeration technology. Herein, the present work reports on the magnetocaloric effect of La0.7Ca0.3Mn1−xSnxO3 (x = 0.0, x = 0.02 and x = 0.04) compound samples produced with the solid state reaction technique. Curie temperature TC obtained for the La0.7Ca0.3Mn1−xSnxO3 (x = 0.0, x = 0.02 and x = 0.04) are 260 K, 176 K and 170 K with -ΔSM max of 4.32 Jkg -1 K -1 , 1.61 Jkg -1 K -1 and 1.24 Jkg -1 K -1 and a refrigerant capacity of 48 J/kg, 41.43 J/kg and 28.53 J/kg for x = 0.0, x = 0.02 and x = 0.04, respectively. A small addition of Sn-doped resulted in a significant decrease of more than 80 K on the Curie temperature scale compared to that of La0.7Ca0.3MnO3. The large gap in the decreasing magnetic temperature phase transition might be useful as an option of metal/transition metal doped for tuning the Curie temperature of magnetic refrigerant materials.

Large Magnetic Entropy Change in La 0.6 Ce 0.4 Fe 11.5 Si 1.5 Alloy Exhibiting First- and Second-Order Phase Transitions

A polycrystalline alloy ingot of La_0.6Ce_0.4Fe_11.5Si_1.5 was prepared by an arc-melting method. Magnetic measurements of magnetization M as a function of field H and temperature T show a ferromagnetic-paramagnetic phase transition at a Curie temperature TC = 170 K. Interestingly, curves of H/M versus M² have a positive slope at low field (H ≤ 10 kOe), which corresponds to a second-order phase transition (SOPT), but a negative slope at high field (H > 10 kOe), which corresponds to a first-order phase transition (FOPT). The magnetic entropy change ΔS_m(T) under different ranges of field change ΔH, calculated from M(H) isotherms, has a maximum IΔS_maxI around TC that increases in magnitude with increasing ΔH. Refrigerant capacity (RC), indicative of magnetic cooling efficiency, also increases with increasing ΔH. Curves of ΔS_m(T)/ΔS_max versus θ = (T - TC)/(Tr - TC), where Tr is the reference temperature, collapse into a universal curve when ΔH ≤ 10 kOe. In contrast, curves of ΔS_m(T)/ΔS_max versus θ do not reduce to a universal curve when ΔH > 10 kOe. These suggest a coexistence of FOPT and SOPT properties in the alloy.

Magnetic properties and magnetocaloric effect studies for La 0.6 Ce 0.4 Fe 11.5 Si 1.5

In this report, we have investigated the magnetic properties and magnetocaloric effect (MCE) of arc-melted La0.6Ce0.4Fe11.5Si1.5. The compound has been prepared by arc-melting of stoichiometric pure elements on a water-cooled copper hearth under an argon atmosphere . Then, the product was sealed in a fused-silica jacket under vacuum and annealed at 1323 K . The measured magnetization as a function of temperature between 100 and 350 K indicated that the compound exhibited a ferromagnetic-paramagnetic (FM-PM) phase transition at 182 K . In addition, based upon the studies for the magnetic field and temperature dependences of magnetization, it should be concluded that the compound underwent a first-order magnetic phase transition.