Improvement of refrigerant capacity of La0.7Ca0.3MnO3 material with a few percent Co doping

The influence of first and second order magnetic phase transitions on the magnetocaloric effect (MCE) and refrigerant capacity or relative cooling power (RCP) of La0.7Ca0.3MnO3 and La0.7Ca0.3Mn0.95Co0.05O3 materials has been investigated. Large low-field-induced magnetic entropy changes are observed in La0.7Ca0.3MnO3 and La0.7Ca0.3Mn0.95Co0.05O3 materials. The La0.7Ca0.3MnO3 material experiences a large entropy change with a first-order magnetic phase transition at the Curie temperature, T-C. On the other hand, La0.7Ca0.3Mn0.95Co0.05O3 displays a smaller entropy change with a second order phase transition. While a first-order magnetic transition material induces a larger MCE (7.528 J/kg K at 5 T) at T-C, this is limited to a narrow temperature range, resulting in a relatively small RCP (218 J/kg), while the Co-doped second-order magnetic transition material induces a smaller MCE (7.14 J/kg K for 5T), but it is spread over a broader temperature range, resulting in a larger RCP (308 J/kg). The maximum magnetoresistance (MR, defined as rho(0)/rho(H)-1) under a field of 5 T is about 206% and 333% for La0.7Ca0.3MnO3 and La0.7Ca0.3Mn0.95Co0.05O3, respectively. The refrigeration capacity (RCP) is enhanced in La0.7Ca0.3Mn0.95Co0.05O3 (by about 41%) due to small changes from Co doping. The magnetocaloric features of these materials at lower magnetic fields (MCE = 3.163 for La0.7Ca0.3Mn0.95Co0.05O3 and 4.63 J/kg K for La0.7Ca0.3MnO3 at 1 T), and the high RCP and MR can provide some ideas for exploring novel magnetic refrigerants that can operate with permanent magnets rather than superconducting ones as the magnetic field source. (C) 2010 Elsevier B.V. All rights reserved.