Influence of Layer-Thickness Ratio on Magnetic Properties in F-La2/3Ca1/3MnO3/AF-La1/3Ca2/3MnO3 Bilayers

Magnetic properties were investigated in ferromagnetic/antiferromagnetic bilayers based on a Ca-doped lanthanum manganite system via hysteretic loops, La_1?x Ca _x MnO₃ grown in?situ on (001) oriented SrTiO₃ crystalline substrates by using a dc sputtering technique at high-pressure (3.5?mbar) pure oxygen as sputter gas and at a substrate temperature of 850?^°C. We grew the antiferromagnetic layer La_1/3Ca_2/3MnO₃ (AF-LCMO) with a given thickness, t _AF, and the ferromagnetic layer La_2/3Ca_1/3MnO₃ (F-LCMO) with a given thickness, t _F. We produced two series of samples: the first one with thickness ratio, t _F/t _AF, of 1/6 and 6/1, maintaining constant the total thickness of the bilayer to 70?nm, and the second one with t _F/t _AF of 3/25, 9/25, 15/25, maintaining constant the antiferromagnetic thickness to 25?nm. Magnetization versus applied field loop was strongly dependent on the t _F/t _AF ratio, which was influenced by both the strains presented in very thin films originated during the growth of the bilayer and the magnetic moment interaction at the ferromagnetic/antiferromagnetic interface due to changes of the electronic structure in this strongly correlated system.