Dielectric permittivity and electrical conductivity in magnetic nanoassemblies in c-ZrO2 upon adding Cr4+(3d2) spins

Inclusion of magnetic spins such as Cr⁴⁺(3d₂) in cubic zirconia c-ZrO₂, a dielectric oxygen ion conductor, is useful to tailor functional dielectric, electrical, and magnetic properties in a single system for several applications. A simple liquid polymer precursor containing Cr⁴⁺ and Zr⁴⁺ ions in a dispersed structure via glycerol is explored to prepare a solid solution CrO₂-ZrO₂ at a moderate pressure 1.5 atm. A recovered powder when heated at moderate temperature 500-800°C in ambient air yields a single phase compound of small crystallites (5-10 nm) in a c-ZrO₂ like stabilized phase. In this process, as much CrO₂ as 20 mol% has been dissolved. At room temperature, a sample having 20 mol% CrO₂ (heated at 500°C) exhibits a magnetic hysteresis loop with large coercivity 794 Oe, but small saturation magnetization 1.64 emu/g and remanent ratio 0.253. At low frequencies such as ~1 kHz, the dielectric permittivity (ε_r) stays nearly constant ~30 (close to the value 35 in pure c-ZrO₂) over a wide temperature range 30-200°C before it increases regularly with temperature, c.