A phenomenological approach to the anisotropic magnetoresistance and planar all effect in tetragonal La2/3Ca1/3MnO3 thin films

摘要

A La2/3Ca1/3MnO3 Hall bar with its long dimension roughly along the hard axis [110] was fabricated on a single-crystal-like tensilely strained film on SrTiO3(001). The anisotropic magnetoresistance (AMR) and planar Hall effect (PHE) have been studied at various external magnetic fields and temperatures. A phenomenological model in the high field limit is developed, and the galvanomagnetic tensor based on a tetragonal symmetry 4/mmm (D4h), applicable to epitaxial films on a substrate, has been obtained by expanding the tensor to the sixth order. The derived in-plane transverse resistance Rxy shows a sin 2φM angular depende nce, while the longitudinal Rxx is constituted by not only a two-fold cos 2φM term, but also a four-fold cos 4φM term due to the square symmetry of the lattice. The model is in good agreement with the experimental results in high fields, while deviations are observed near the100 easy axis with the decreasing field. Close inspection of the fitting parameters reveals the evolution of these term weights with temperature and magnetic field, which is distinct from conventional ferromagnetic metals and cannot be explained by the phenomenological model. An alternative mechanism for AMR, stemming from the magnetization-induced local orbit deformation through spin–orbit interaction, as previously proposed by O’Donnell et al, may be prevalent in manganites and other systems of complicated crystal structure.