Oxygen nonstoichiometry and magnetotransport properties of Sr2(Y1−xCax)Co2O7+δ cobalt oxides

Tunability of oxygen nonstoichiometry of the Co-based Ruddlesden–Popper phase, Sr2(Y1−xCax)Co2O7+δ, has been investigated using single-phase samples obtained by means of solid-state synthesis within 0.3≤x≤0.5. With cerimetric titrations and thermogravimetric measurements carried out in O2 and Ar atmospheres, it is found that wide-range oxygen tuning is possible over the whole range of cation stoichiometry, 0.3≤x≤0.5. The minimum oxygen content corresponds to δ≈−1.2 for all the samples (with 0.3≤x≤0.5), while the maximum amount of oxygen loaded in the structure upon 1 atm O2 annealing increases as x decreases, reaching δ=−0.52 at x=0.3. The change in oxygen nonstoichiometry is reflected in the magnetic and magnetotransport properties of the phase. A small magnetoresistance effect (up to ∼3.5%) is revealed for the oxygenated samples at low temperatures.