Influence of film thickness and strain on magnetic properties of epitaxial La 0.7 A 0.3 CoO 3 (A = Ca, Sr, Ba) thin films

We prepared La 0.7 A 0.3 CoO 3 (A=Ca, Sr, Ba) films with a thickness ranging from 50 up to 1000 monolayers (∼ 20–400 nm) by pulsed laser deposition (PLD) on (001)‐oriented single crystal substrates of SrTiO 3 , (LaAlO 3 ) 0.3 (Sr 2 AlTaO 6 ) 0.7 and LaAlO 3 and studied the in‐plane and out‐of‐plane magnetization as function of thickness and of the strain provided by the substrate‐film lattice mismatch. The Curie temperature T C decreases slightly with thickness according to the finite size scaling 1 – T C / T ∞ = ( N 0 / N ) λ , where T ∞ is the bulk Curie temperature and N is the number of monolayers. We obtain a critical exponent λ = 0.9 ± 0.2, consistent with the theoretical mean field value, and a spin‐spin coupling range N 0 = 2–3.