Magnetic Properties of Nickel-Iron Ferrite

Abstract

The magnetic anisotropy of a single crystal of nickel-iron ferrite with composition Fe1.003+[Ni0.792+Fe0.363+Fe0.903+]O4 is given between 450 and 4.2°K. At high temperatures the anistropy energy has cubic symmetry, and the absolute value of the first-order anisotropy constant is a maximum at ca 200°K. Below 200°K, |K1| decreases until 10°K, at which temperature there is an abrupt transition in the anisotropy characteristics. Below 10°K the anisotropy energy contains a uniaxial term of the form Εi αi2βi2 where αi and βi are the direction cosines of the magnetization at the measuring temperature and at the annealing temperature (10°K), respectively. This low-temperature behavior has been explained on the basis of existent theory of magnetic annealing. The model used to explain the uniaxial anisotropy term given above is shown to be consistent with the noncubic anisotropy energy obtained upon cooling the sample through 10°K in the absence of an external field. The model is also shown to lead directly to a relaxation effect which contributes a term of the form K′(α12α22+α22α32+α32α12) to the anisotropy energy above 10°K and explains the observed maximum in |K1|.