关键词: 磁热效应/
磁熵变/
磁相变
English Abstract
Magnetic and magnetocaloric effects of Eu0.9M0.1TiO3 (M=Ca, Sr, Ba, La, Ce, Sm) compounds
Hao Zhi-Hong1,Wang Hai-Ying1,
Zhang Quan1,
Mo Zhao-Jun2
1. School of Optometry, Tianjin Vocational Institute, Tianjin 300410, China;
2. School of Material Science and Engineering, Institute of Material Physics, Tianjin University of Technology, Tianjin 300384, China
Received Date:21 September 2018
Accepted Date:19 October 2018
Published Online:20 December 2019
Abstract:EuTiO3 is a direct band-gap semiconductor material and exhibits antiferromagnetism with large magnetic entropy change around the liquid helium temperature. The ferromagnetic state can be changed into antiferromagnetic state through lattice constant change and electron doping by element substitution due to strong spin-lattice coupling coexistence of ferromagnetic coupling, and antiferromagnetic coupling. The values of magnetic entropy change can be effectively improved under low magnetic field change after changing into ferromagnetism. Samples of EuTiO3 and Eu0.9M0.1TiO3 (M=Ca, Sr, Ba, La, Ce, Sm) are prepared by the sol gel method. The Eu0.9Ca0.1TiO3 exhibits the antiferromagnetism due to similar ion radius. The ferromagnetic coupling between Eu0.9Sr0.1TiO3 and Eu0.9Ba0.1TiO3 is enhanced, for alkaline earth metal (Sr and Ba) has larger ion radius, which is beneficial to improving the magnetocaloric effect under low magnetic field. Electron doping can inhibit the antiferromagnetic coupling because the extra carrier may occupy the Ti 3d and reduce the hybridization of Eu 4f-Ti 3d-Eu 4f. When the electron doping concentration is greater than 10%, the spin polarization rate of Ti 3d state on the Fermi surface is negative, resulting in the transition from antiferromagnetic to ferromagnetic state. When the Eu ions are replaced with the Sm ions (Sm ion radius is similar to Eu ion radius), the ferromagnetic coupling is enhanced. However, when the Eu ions are replaced with the La or Ce ions, the samples show strong ferromagnetism, for the lattice constant and electron doping are increased. A giant reversible magnetocaloric effect and large refrigerant capacity for each of Eu0.9M0.1TiO3 (M=Sr, Ba, La, Ce) compounds are observed. Under the magnetic field change of 1 T, the values of maximum magnetic entropy change and refrigeration capacity are 9.8 J/(kg·K) and 36.6 J/kg for Eu0.9Sr0.1TiO3, and 10 J/(kg·K) and 45.1 J/kg for Eu0.9Ba0.1TiO3. The values of maximum magnetic entropy change of Eu0.9La0.1TiO3 and Eu0.9Ce0.1TiO3 are 10.8 J/(kg·K) and 11 J/(kg·K), respectively, which are larger than that of EuTiO3 (9.8 J/(kg·K)). The values of refrigeration capacity are 39.3 J/kg and 51.8 J/kg, which are also improved compared with those of EuTiO3. In a word, the results suggest that these compounds could be considered as good candidates for low-temperature and low-field magnetic refrigerant.
Keywords: magnetocaloric effect/
magnetic entropy change/
magnetic phase transition
