Temperature Dependence of Planar Hall Effect and Anisotropic Magnetoresistance in Phase-Separated (La_1-yPr_y)_1-xCa_xMnO₃ Thin Films

Electronic phase coexistence between the ferromagnetic metallic (FMM) and insulating phases of the perovskite manganite (La_1-yPr_y)_1-xCa_xMnO₃ (LPCMO) leads to unique electronic and magnetic properties at low temperatures. In particular, uniaxial, in-plane magnetic anisotropy has been induced in thin films by anisotropic strain from the substrate, (110) NdGaO₃ (NGO). However, on the scale of millimeters, the LPCMO thin films do not show clear anisotropic transport or anisotropic magnetoresistance (AMR) associated with the magnetic anisotropy. We have fabricated millimeter scale structures using photolithography to measure both the AMR and planar Hall effect (PHE). The combination of AMR and PHE measurements reveal uniaxial anisotropy at low fields. This anisotropy decreases as the temperature is increased close to the metal-insulator transition temperature. Our data suggest that the uniaxial anisotropy is proportional to the size of the FMM regions in the thin film and not just on the anisotropic strain. PHE measurements are a technique that can also be used to measure the magnetic coercive field and magnetic anisotropy of manganite microstructures. Hence, we can measure the variation of magnetic anisotropy as the sample size is decreased to the scale of phase separation in LPCMO.