Exchange Interaction and Cubic Crystal Field Splitting Parameter of Fe³⁺ in Spinel Structure

Abstract

The line widths of paramagnetic resonance absorption of Fe³⁺ ions in MgAl₂O₄ and ZnAl₂O₄ polycrystals and of Mn²⁺ ions in ZnAl₂O₄, having the same spinel crystal structure as ferrite, are measured as a function of concentration.
The cubic crystal field splitting parameters a of Fe³⁺ ion at A- and B-sites are determined from the line widths extrapolated to zero concentration: a_A=1.0×10⁻² cm⁻¹ and a_B=3.1×10⁻² cm⁻¹. a_B⁄a_A=3.1.
On the other hand, the magnitudes of exchange integral between Fe³⁺ ions in A- and B-sites or in B- and B-sites are estimated from the decrease of line width due to exchange narrowing as the concentration increases, namely, J_AB⁄gβ=1.32×10⁵ Oe and J_BB⁄gβ=1.90×10³ Oe. The Curie temperatures obtained from the exchange integral are in agreement with the Curie temperatures of Mg-ferrite and Zn-ferrite measured experimentally.