Abstract
Magnetic properties of ZnxFe1−xO nanopowder and Zn1−x−yFexMgyO ceramic samples are investigated at temperatures between T=(5–400) K, showing in the latter compound ferromagnetic (FM) interactions up to T∼330 K. When the Fe and Mg concentrations are increased, the amplitude of the Fe3+ electron spin resonance lines decrease while the FM resonance lines grow. The Curie–Weiss type temperature dependence of the magnetization M(T)∝1/T observed for Zn0.89Fe0.01Mg0.10O suggests that in this sample the magnetic interactions are caused by single polarons and small clusters. Strong growth of M(T) and room temperature ferromagnetism are observed in Zn0.70Fe0.04Mg0.26O where the magnetic susceptibility follows the scaling law [χ−1(T)−χ−1(Tc)]∼(T/TC−1)γ with exponents γ1=1.43 typical of three-dimensional (3D) Heisenberg spin systems above the critical temperature Tcr=330 K, and γ2=1.75 characteristic of 3D cluster percolation below Tcr. The estimated critical cluster radius is 40 nm. The M(B) curves are anhysteretic and no time dependence of the thermoremanent magnetization is observed.
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