Thickness dependent magnetic anisotropy of ultrathin LCMO epitaxial thin films

TL;DR

This study investigates how the magnetic anisotropy of ultrathin LCMO films varies with thickness, revealing in-plane easy axes and the preservation of ferromagnetism down to 3 nm without dead layers.

Contribution

It provides detailed insights into the thickness-dependent magnetic anisotropy and easy axis orientation in ultrathin LCMO epitaxial films, a novel characterization in this material system.

Findings

LCMO films remain ferromagnetic down to 3 nm without dead layers.

Magnetic easy axes are in-plane for 4-15 nm films.

Easy axes directions differ by 45° at 4 nm and 15 nm thicknesses.

Abstract

The magnetic properties of La0.7Ca0.3MnO3 (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 approx. 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 SrTiO3 substrate differ by 45 degrees in 4 nm and 15 nm thick LCMO films.