Measurement of the anisotropy constant in Ni-Fe and Fe3O4 magnetic fluids

Lambrick, David B., Hoon, Steve R., Mason, N. and Kilner, M. (1988) Measurement of the anisotropy constant in Ni-Fe and Fe3O4 magnetic fluids. IEEE transactions on magnetics, 24 (2). pp. 1647-1649. ISSN 0018-9464

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Abstract

The uniaxial anisotropy constant of two magnetic field systems has been measured using magnetization and torque magnetometry. A metallic, Ni-Fe system was frozen at 77 K to obtain torque curves while an Fe3O4 system was set in a polyester resin at room temperature in the presence of aligning magnetic fields. The induced texture gave rise to torque measurements which yielded values for the anisotropy constant of 2.9*105 Jm-3 for Ni-Fe and 0.58*105 Jm-3 for magnetite. The magnetization measurements resulted in lower values of 1.15*105 Jm-3 for Ni-Fe and 0.47*105 Jm-3 for Fe3O4. Even for the lowest value obtained, however, a particle elongation of 1.5 would be required for shape to be responsible for the anisotropy. No such elongations were observed in the electron microscope suggesting other factors are present.