Effect of Co Doping on the Structure and Magnetic Properties of TmMn1-xCoxO3

We report the structure and magnetic properties of Co-doped TmMnO3 polycrystals for Co doping levels of 0 ≤ x ≤ 0.9. TmMnO3 (x = 0) prepared at ambient pressure was hexagonal. Hexagonal and orthorhombic phases coexisted in TmMn1−xCoxO3 for 0 ≤ x < 0.5. We obtained almost single-phase orthorhombic samples with 0.5 ≤ x ≤ 0.9 using complex polymerization. Ferromagnetic orthorhombic TmMn1−xCoxO3 formed upon Co doping. The ionic states of Tm, Mn, and Co were determined through magnetization measurements. The rapid decrease in magnetization for 0.5 ≤ x ≤ 0.7 below about 25 K was explained using a model consisting of a combination of ferromagnetic Mn–Co and paramagnetic Tm sublattices