Contribution of the Fe²⁺ ion to the magnetic anisotropy constant in ferrites

Abstract

The magnetic anisotropy constant Kl originating from the presence of Fe2+ ions in ferrites is calculated, using the theory of Wolf, for a case that the electron hopping between FeS+ and Fea+ ions is allowed within a cluster of iron ions around some lattice defects. The calculated value of Kl exhibits a characteristic temperature dependence, i.e. the change of the sign from positive a t lower temperatures to negative at higher temperatures. It is ahown that the result well agrees with the Fez+ contribution to Kl estimated from the available data of the anisotropy constant for the Nil -zFe2+z04 system.Die magnetische Anisotropiekonstante Ill in Ferriten, die in der Existenz der Fe2+-Ionen ihre Ursache hat, wird fur den Fall, daD die Elektronenwanderung von Fe2+-zu Fe3+-Ionen in einem Cluster von einigen Eisenionen um einen Gitterdefect erlaubt ist, mit der Theorie von Wolf bereohnet. Die Ergebnisse dieser Rechnungen zeigen eine charakteristische Temperaturabhiingigkeit von K,, d. h. eine Bnderung des Vorzeichens von plus bei tiefen Temperaturen zu minus fur hohere Temperaturen. Es wird gezeigt, diLB diese Ergebnisse mit dem Fe2+-Beitrag zu K,, der aus der bekannten GroDe der Anisotropiekonstante fur das System Nil -zFe2 +$04 abgeschatzt wurde, recht gut ubereinstimmt.

Magnetoresistance of magnetite

“…Indeed, the analysis of torque magnetometry data indicated that the Fe 2+ contribution to K 1 changes sign above the Verwey temperature [31]. Thus, the sign change in K 1 from positive to negative values, observed in magnetite at about 130 K, was attributed to the gradual electron delocalization with rising temperature [32]. This interpretation might also apply to the observed sign change of the AMR.…”

Magnetic Anisotropy and Magnetostriction of Gallium Ferrous Ferrites

“…For x 2 0.7, K1 changes sign to a positive value at low temperature, whereas for x 5 0.4, K1 remains negative in the whole cubic phase temperature region, and becomes even more negative approaching the Verwey-temperature. The temperature dependence of K1 for large Ga content can be explained by the Watanabe model [9] in which at low temperature K1 becomes positive due to the ionic Ga-Fe disorder on B-sites. For x 5 0.4 the additional decrease of the negative K1 at lower temperatures (see Fig.…”

Magnetic Anisotropy of Disordered Magnetics with Jahn‐Teller Ions

“…Random fields stabilize one of the four A1, states and a situation typical of the static Jahn-Teller effect takes place a t sufficiently low temperatures. A similar qualitative study of the contribution of Fez+ ions to the cubic anisotropy constant was carried out in [6].…”

“…Watanabe et al [6] calculated the contribution of Fez+ ions to the first anisotropy constant for the case when the electron hopping between Fez+ and Fe3+ ions is allowed within the cluster of iron ions.…”