Nanocrystalline MnFe2O4 produced by niobium doping

Nanosized MnFe2O4 phase with diameters in the range 13.7 to 100 nm were produced by calcination and sintering treatments in the system zNb(2)O(5) .(50 - z)MnO . 50Fe(2)O(3) with z having values between 0 and 20. Nb5+ ions an believed to give rise to vacancies in the Mn2+ sites, which break up the coupling of ferrimagnetically active oxygen polyhedra. The Curie temperature decreases as the size of the MnFe2O4 phase is reduced. This is explained on the basis of a decrease in the number of exchange pairs of the type Mn2+-Fe3+. The coercivity increases with a decrease in the size of the ferrimagnetic phase. This is believed to arise due to a decrease in saturation magnetization as the size of the MnFeO4 phase is reduced.