Finite size effect in epitaxial La 0.7A 0.3CoO 3 (A=Ca, Sr, Ba) thin films

Abstract

The in-plane and out-of-plane magnetization of La 0.7A 0.3CoO 3 thin films with A=Ca, Sr, or Ba were investigated as a function of the film thickness ranging from about 10 to 1000 monolayers. Nearly lattice matched epitaxial (0 0 1) oriented films have been grown by pulsed laser deposition on (LaAlO 3) 0.3(Sr 2AlTaO 6) 0.7 substrates. Their magnetic properties were characterized by SQUID measurements. Field cooled measurements were carried out with the field parallel or perpendicular to the film surface. All the films showed a finite size scaling law without any sign of a spin reorientation down to at least 10 monolayers. For the critical exponent we obtained λ≈0.9±0.2. For the model parameter No, discussed as the spin–spin coupling length we obtained 2–3 monolayers which compares well with the value measured for Co films.