Abstract :
Electron paramagnetic resonance spectroscopy was used for studying the effect of allied and alien ions on the EPR spectrum of Mn4+-containing lithium–manganese spinel oxides. Manganese spinel oxides with paramagnetic Mn4+ and diamagnetic substituents in the 16d spinel sites were studied: Li[Mg0.5Mn1.5]O4, Li[Mg0.5−xCo2xMn1.5−x]O4, 0<x≤0.5, and Li[Li1/3Mn5/3]O4. Ni2+-ions with integer-spin-ground state (S=1) were selected as alien ions: Li[Mg0.5−xNixMn1.5]O4 (0≤x≤0.5), Li[Li(1−2x)/3NixMn(5−x)/3]O4 (0≤x≤0.5), and Li[Ni0.5Mn1.5−yTiy]O4 (0≤y≤1.0). It was shown that in Ni-substituted oxides the low temperature EPR response comes from magnetically correlated Ni–Mn spins, while at high registration temperature Mn4+ ions give rise to the EPR profile. Analysis of the EPR line width allows differentiating between the contributions of the density of paramagnetic species and the strength of the exchange interactions in magnetically concentrated systems. The density of allied and alien paramagnetic species has no effect on the EPR line width in cases when the strengths of antiferro- and ferromagnetic interactions on an atomic site are close. On the contrary, when antiferro- or ferromagnetic interactions on an atomic site are dominant, the EPR line width increases with the density of paramagnetic species.
