Magnetic Study of ZnMnO₃ in ZnO/MnO Nanocomposites

Three nanocrystalline samples of ZnO doped with MnO (with 20, 30, and 40 wt% of MnO in initial mixture) were synthesized by the wet chemical method. Previous X-ray diffraction study has found that they contained only hexagonal ZnO and cubic ZnMnO
₃
nanocrystals. DC magnetization study revealed a paramagnetic (PM) state above 50 K, the presence of mixed valence of Mn ions (Mn
³⁺
and Mn
⁴⁺
) and an important role played by magnetic clusters influencing the behavior of the effective magnetic moment and effective interaction type. Low temperature results indicated a chain of magnetic transformation from PM to ferrimagnetic, to superparamagnetic and to blocked states. Electron spin resonance (ESR) provided additional information about magnetic relaxation of the spin clusters and possible location of separate Mn
²⁺
and Mn
⁴⁺
ions. Large magnetic inhomogeneity of our samples was evidenced, and it is the result of magnetic ions clustering, various valences of Mn ions, distribution of nanoparticle sizes, and competition of magnetic interactions.