Double Exchange Via T(2g) Orbitals And The Jahn-Teller Effect In Ferromagnetic La0.7sr0.3coo3 Probed By Epitaxial Strain

The magnetic exchange in hole-doped ferromagnetic cobaltates is investigated by studying the magnetic and electronic properties of La0.7Sr0.3CoO3 films as a function of epitaxial strain. We found a strong-coupling double exchange mechanism between Co3+(4t(2g) 2e(g)) and Co4+(3t(2g) 2e(g)) high-spin states mediated by t(2g) electrons-in contrast to the moderate coupling provided by the e(g) exchange in manganites. The strong sensitivity of the Curie temperature T-C to the bulk compression can be explained by the small bandwidth of the t(2g)-derived states. A strain-induced Jahn-Teller effect is likewise observed. The experimental results clarify the magnetic exchange mechanism in the cobaltates.