The correlation between electric and thermoelectric properties in percolative Co/Al₂O₃, Co/SiO₂ and Co/TiO₂ ferromagnetic nanocomposites

DOI: 10.62564/M4-OB1326

Oleksii Baibara¹, Marina Bugaiova¹, Yaroslav Stelmakh², Larisa Krushinskaya², Arsenii Ievtushenko<sup>1

1</sup>Frantsevich Institute for Problems of Materials Science National Academy of Science of Ukraine
²E.O. Paton Electric Welding Institute, Ukraine


Ferromagnetic nanocomposites (FMNC), consisting of ferromagnetic nanoparticles distributed in a dielectric matrix, behaves as a disordered system in the strongly localized regime [1,2]. Granular structure determines the specific properties of FMNCs, in particular, the metal–insulator transition induced by a change in metal content x, so below percolation threshold, the metallic granules in ferromagnetic nanocomposites are separated by dielectric layers, and hopping transport (HT) to be predominant. From a structural point of view, FMNCs are different from doped materials, therefore, debate arises in how to extend the HT model of doped materials to granular composites. One of the primary concerns focuses on the value of characteristic temperature T₀. Ferromagnetic nanocomposites with Co nanoparticles distributed in various dielectric amorphous matrixes Al₂O₃, SiO₂ and TiO₂ were grown by the EB-PVD method in the form of film with thickness from 0.8 to 10 μm on Al₂O₃ substrates (polycor). The Cо concentration x varied in wide region from 10 to 70 at.% for all matrixes. The temperature dependences of the resistance and thermoelectric properties for FMNCs Co/Al₂O₃, Со/SiO₂ and Co/TiO₂ were investigated in the temperature range of 77 ÷ 290 K. Electric properties of FMNC were fitted by formula ρ =ρ₀exp(T₀/T)n with best fit corresponds to the value of n≈1/2. It has been shown that the value of the characteristic temperature T₀ depends from the concentration of Co and proportional s/d, where s is separations between NPs and d is the diameter of NPs. We have shown, that the temperature dependence of thermoelectric power is well described by an empirical formula α(T)~Tt/T+T where m weakly depends from concentration of Co and the superparamagnetic state of Co nanoparticles, and Tt correlated with characteristic temperature T₀.

Keywords
nanocomposites, Co nanoparticles, percolation, hopping transport, thermoelectric power

Acknowledgments
Not provided

References
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