Structural and magnetic properties of the La2−xCaxCoIrO6 double perovskite series

• Novel double perovskite series La2−xCaxCoIrO6 were synthesized by solid state reaction.
• La3+ to Ca2+ substitution leads to Co valence and possibly spin state changes.
• For some doped compounds, the emergence of a second magnetic phase, due to the presence of high spin Co3+, becomes evident.
• Physical properties of each compound can be well correlated to the electronic and magnetic evolution of the system.

Polycrystalline samples of the series La2−xCaxCoIrO6 (0≤x≤1.20≤x≤1.2) have been synthesized and its structural and magnetic properties were investigated using experiments of X-ray powder diffraction, temperature dependent magnetic susceptibility and magnetization as a function of applied magnetic field. All grown polycrystalline compounds form in a monoclinic structure (space group P21/nP21/n) with a partially ordered distribution of transition metal cations Co/Ir over the six-coordinate sites. Our results indicate variation of the magnetic interactions between Co and Ir magnetic sublattices possibly due to valence changes of the transition metals, induced by doping. The undoped La2CoIrO6 presents magnetic ordering at ~97K, while for Ca-doped compounds a decrease of net magnetization and ordering temperatures was observed. For x=0.2 and 0.5 the emergence of a second magnetic interaction, due to the presence of high spin Co3+, becomes evident. Interestingly, for x=0.8 the large effective magnetic moment indicates strong orbital contribution and spin-orbit coupling and/or the presence of Co4+ in high spin state.

Field cooling M vs.T   curves for La2−xCaxCoIrO6La2−xCaxCoIrO6 shows the suppression of magnetism with increasing La content. Zero field cooled curves indicate a second magnetic phase induced by the appearance of Co3+Co3+.Figure optionsDownload as PowerPoint slide