Tian Miao

A large enhancement of magnetocaloric effect by chemical ordering in manganites

For conventional ferromagnetic systems, the magnetocaloric effect (MCE) is dominated by the entropy changes upon magnetic phase transitions. For strongly correlated oxides such as manganites, in which competing magnetic orders coexist and respond to an external field differently, the MCE is more complex due to the electronic phase separation (EPS) phenomenon. Taking the well-known (La2/3Pr1/3)5/8Ca3/8MnO3 (LPCMO) manganite as a model system, we investigated how the length scale of EPS phases affects the MCE. Specifically, the EPS length scale can be dramatically reduced by the spatial ordering of Pr dopants in the LPCMO system. Experimental results indicate that the magnetic entropy change of the Pr-ordered LPCMO is considerably larger than that of the Pr-random LPCMO by a factor up to six at the onset temperature of the ferromagnetic phase. A direct relation between the length scale of EPS and MCE has been established based on the experimental results.

A strain-induced new phase diagram and unusually high Curie temperature in manganites

Raising the critical temperature of functional materials is a major challenge for the exploitation of many exciting physical phenomena, such as high-Tc superconductivity, colossal magnetoresistance, and multiferroicity in strongly correlated systems. To this end, chemical doping, pressure, epitaxial strain, electric gating, interfacial charge transfer, and symmetry broken effects at the surface or edge have been used as the major means. While all these efforts have had some success, room temperature remains as the highly desirable yet difficult hurdle to clear. In this work, we demonstrate that the Curie temperature of a manganite system can be raised to over 300 K by tuning the epitaxial strain and chemical doping, and explain the underlying mechanism based on density functional theory (DFT) calculations and Monte Carlo (MC) simulations. Furthermore, we successfully designed a room temperature spin injector in a magnetic tunnel junction device based on the high-Tc manganite.