Magnetic Properties of Field Cooled Coca Ferrite Nanoparticles

Abstract

We investigated the magnetic properties of field cooled CoCa ferrite (Co_1-xCa_xFe₂O₄) nanoparticles. The magnetizations and coercivities of field cooled Co_1-xCa_xFe₂O₄ nanoparticles show the maximum at x=0.2 in the nominal composition x ranged from 0 to 0.4. In x=0.1 to 0.4, the coercivities monotonically increase with decreasing cooling rate, while field cooled CoFe₂O₄ nanoparticles, which corresponds to x=0 in Co_1-xCa_xFe₂O₄, do not depend on the cooling rate in our condition (1.25°C/min-15°C/min). The enhanced coercivities should be attributed to the filed cooling condition. The induced magnetic anisotropy of field cooled Co_1-xCa_xFe₂O₄ nanoparticles would originate from the surface layer.