tailieunhanh - Báo cáo "Effects of Zn content on the magnetic and magnetocaloric properties of Ni-Zn ferrites "

Among spinel ferrites, Cd and Zn ferrites are always normal ferrites with Cd and Zn ions locating only in tetrahedral sites. This study presents effect of Zn on the magnetic and magnetocaloric properties of the mixed spinel ferrites Ni1-xZnxFe2O4 (x = , , , ). The presence of Zn affects lattice parameters, saturation magnetization Ms, Curie temperature, Tc, and magnetic entropy change ∆Sm. At highest Zn content, Tc reduces to the temperature lower than room temperature and magnetic structure of spins in the octahedral sublattice should be strongly canted. . | VNU Journal of Science Mathematics - Physics 24 2008 155-162 Effects of Zn content on the magnetic and magnetocaloric properties of Ni-Zn ferrites N. Chau1 . Thuan1 . Minh2 . Luong1 1 Center for Materials Science College of Science VNU 334 Nguyen Trai Hanoi Vietnam 2 Department of Solid State Physics College of Science VNU 334 Nguyen Trai Hanoi Vietnam Received 20 August 2008 Abstract. Among spinel ferrites Cd and Zn ferrites are always normal ferrites with Cd and Zn ions locating only in tetrahedral sites. This study presents effect of Zn on the magnetic and magnetocaloric properties of the mixed spinel ferrites Ni1-xZnxFe2O4 x . The presence of Zn affects lattice parameters saturation magnetization Ms Curie temperature Tc and magnetic entropy change ASm. At highest Zn content Tc reduces to the temperature lower than room temperature and magnetic structure of spins in the octahedral sublattice should be strongly canted. The maximum magnetic entropy change occurs in a large temperature range from low temperature to hundreds of Celcius degrees. Keywords ferrite magnetocaloric effect. 1. Introduction It is well known that spinel ferrites consist of three types of magnetic structures normal inverse and mixed spinel 1 . In normal spinel the divalent ions locate at tetrahedral sublattice A-site and trivalent ions Fe3 locate at octahedral sublattice B-site . In inverse spinel a half of Fe3 ions locates at A site and the rest Fe3 ions together with divalent ions locate at B site. In mixed spinel ferrite both Fe3 ions and divalent ions locate at A and B site. NiFe2O4 is inverse spinel ferrite. Among spinel ferrites only Zn and Cd ferrites belong to pure normal structure. Mixed Ni-Zn ferrites have extremely high resistivity so that they are widely used as soft magnetic materials suitable for high-frequency applications. Initial permeability is maximum at 30 mol NiFe2O4 70 mol ZnFe2O4 and this compositon has Curie temperature TC near room .

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