Phase Coexistence-Induced Out-of-Plane Magnetization in Manganite Thin Films

Coexisting magnetic phases in hole-doped manganites such as (La_1-yPr_y)_1-xCa_xMnO₃ (LPCMO) lead to properties not observed in single phase ferromagnets. In particular, out-of-plane (OOP) magnetization is usually difficult to achieve in ferromagnetic thin films due to shape anisotropy. OOP magnetization can be used for Skyrmion formation and in solid state magnetic memory devices such as racetrack memory. We investigated if phase coexistence in LPCMO thin films can be used to produce OOP magnetization. At low temperatures, the mixed phase state in LPCMO consists of a charge ordered insulating (COI) phase, in which nanometer-scale single-domain ferromagnetic metallic (FMM) regions are nucleated and then grow as the temperature decreases before combining into multidomain FMM regions. This single domain to multidomain transition occurs at a critical domain radius of about 100nm. We measured the magnetization vs field loops of a 120nm LPCMO thin film grown on a (110) NdGaO₃ (NGO) substrate using a SQUID magnetometer, with the magnetic field oriented along either the OOP or in-plane easy axis direction. We observed that between 65 K and 80 K there is a clear signature of an OOP easy axis, which suggests that the FMM single domains are smaller than the thin film thickness. Below 60 K the OOP magnetization reverts back to the usual hard axis behavior. Based on these data we will discuss how phase coexistence in LPCMO can be used to control magnetic anisotrpy, including the production of perpendicular magnetic anisotropy.