Structural, electric and magnetic properties of La_1−xSr_xCo_1−xRu_xO₃ (0 ≤ x ≤ 0.6) solid solution

Structural, electrical transport and magnetic properties of La_1−xSr_xCo_1−xRu_xO₃ (0 ≤ x ≤ 0.6) have been investigated. Sr and Ru co-doped LaCoO₃ (LCO) at La and Co sites reveals a structural phase transition from rhombohedral to monoclinic with increase of x. X-ray photoelectron spectroscopy shows that Ru is present in the mixed valence state, Ru⁴⁺ and Ru⁵⁺ accompanied with Co³⁺ and Co²⁺ valencies. Pure LCO reveals a change from charge gap at higher temperature to spin gap at lower temperature in charge transport process. Higher spin configuration of Co³⁺ stabilizes ferromagnetic ground state in LCO. Temperature dependence of electrical resistivity indicates a semiconducting behavior for the entire composition range (0 ≤ x ≤ 0.6). High degree of disorder of Co and Ru ions leads to spin glass and cluster glass phase for x ≤ 0.2. The observation of Curie temperature at about 154 K indicates the phase segregation into ferromagnetic SrRuO₃ (SRO) for x ≥ 0.3. A critical behavior study for the ferromagnetic phase suggests that the ferromagnetism can be described by mean field model. The co-existence of semiconducting and ferromagnetism can be attributed to random distribution of four cations, La, Sr, Co and Ru. - Graphical abstract: Random incorporation of Sr and Ru into LaCoO₃ lattice leads to the structural phase transition from rhombohedral to monoclinic structure above doping concentration 20%. Large mismatch in charge between Ru⁵⁺ and Co²⁺ drives the separation of ferromagnetic SrRuO₃ phase for concentration above 20%. - Highlights: • Structural phase transition from rhombohedral to monoclinic with Sr and Ru doping. • X-ray photoelectron spectroscopy ensures charge transfer between Co and Ru. • Spin glass, cluster glass and ferromagnetic ground state. • Random distribution of Co and Ru favors semiconducting ferromagnetic phase. • Critical behavior analysis supports the mean field model for ferromagnetic phase