Structural Phase Separation, Magnetic and Magnetocaloric Properties of La0.7-xLuxCa0.3MnO3 Ceramics
摘要
La0.7-xLuxCa0.3MnO3 manufactured by the ceramic method have been carefully studied. Structural analyses prove the compound with x = 0.03 exhibiting the monophase in an orthorhombic structure, similar to the parent compound (x = 0). At higher Lu concentrations (x ≥ 0.06), besides the orthorhombic phase, there is an additionally constituted secondary phase of hexagonal LuMnO3. This phase together with the replacement of a smaller Lu3+ ion for a larger La3+ one in orthorhombic compounds would reduce the magnetization. Comparing to x = 0 (TC ≈ 252 K), the Lu doping at x = 0.03 reduced strongly TC to ~ 208 K. However, as x ≥ 0.06, the TC reduction becomes slower, TC ≈ 203 K for x = 0.12. In particular, the Lu doping does not change the phase-transition feature, all compounds still exhibit the first-order character. Near TC, the magnetic entropy change is largest of 4.2~5.8 J/kg K, while the relative cooling power ranges from 120 to ~ 140 J/kg, for a field variation of H = 30 kOe. Comparing with LaMnO3-based magnetocaloric materials, we believe that La0.7-xLuxCa0.3MnO3 compounds are also potential materials for magnetocaloric applications at temperatures T = 200-231 K.