Thickness Dependent Magnetic Anisotropy of Ultrathin LCMO Epitaxial Thin Films

摘要

The magnetic properties of ${rm La}_{0.7}{rm Ca}_{0.3}{rm MnO}_{3}$ (LCMO) manganite thin films were studied with magnetometry and ferromagnetic resonance as a function of film thickness. They maintain the colossal magnetoresistance behavior with a pronounced metal-insulator transition around 150–200 K, except for the very thinnest films studied (3 nm). Nevertheless, LCMO films as thin as 3 nm remain ferromagnetic, without a decrease in saturation magnetization, indicating an absence of dead-layers, although below approximately 6 nm the films remain insulating at low temperature. Magnetization hysteresis loops reveal that the magnetic easy axes lie in the plane of the film for thicknesses in the range of 4–15 nm. Ferromagnetic resonance studies confirm that the easy axes are in-plane, and find a biaxial symmetry in-plane with two, perpendicular easy axes. The directions of the easy axes with respect to the crystallographic directions of the cubic ${rm SrTiO}_{3}$ substrate differ by 45 deg in 4- and 15-nm-thick LCMO films.