Length Scale Dependence of Anisotropic Magnetoresistance in Phase-Separated (La_1-yPr_y)_1-xCa_xMnO₃ Thin Film Microstructures

Electronic phase coexistence occurs in perovskite manganites such as (La_1-yPr_y)_1-xCa_xMnO₃ (LPCMO) between ferromagnetic metallic (FMM) and charge-ordered insulating (COI) phases, leading to unique electronic and magnetic properties. For example, in thin films of LPCMO grown on (110) NdGaO₃ (NGO) substrates, anisotropic strain leads to uniaxial, in-plane magnetic anisotropy. We fabricated micrometer scale Hall bars of nominal size 120 µm x 20 µm, 240 µm x 40 µm, and 540 µm x 100 µm on a thin film (120 nm thickness) through photolithographic methods in order to isolate the properties of several FMM regions which can have sizes on the order of tens of micrometer. Furthermore, we designed a home-built apparatus which could accommodate a 10.5 mm by 7.5 mm chip carrier (needed for the microfabricated Hall bar sample) and perform Planar Hall effect (PHE) and anisotropic magnetoresistance (AMR) measurements. The PHE measurements confirmed uniaxial magnetic anisotropy that had been seen previously in magnetization measurements. Taking advantage of the length scale of our microstructures, we observed the length scaled dependence of PHE and AMR of LPCMO at different magnetic fields and temperatures. We expect that the competition between the shape anisotropy of the FMM regions that are pinned by the microstructure’s dimensions and the magnetic anisotropy due to lattice strain will allow us to tune the magnetic anisotropy of phase-separated manganite thin films.