The role of strain in low-field magnetotransport properties of manganite thin films

Strain-induced large low-field magnetoresistance has been observed in very thin Pr_0.67Sr_0.33MnO₃ films¹ To better understand the role of strain in the low-fie magnetotransport properties of manganite thin films, we have studied and compared very thin (3-20 nm) Pr_0.67Sr_0.33MnO₃ (PSMO), La_0.67Ba_0.33MnO₃ (LBMO), La_0.67Sr_0.33MnO₃ (LSMO) and La_0.67Ca_0.33MnO₃ (LCMO) films grown on different substrates, such as LaAlO₃(001) (LAO), NdGaO₃(110) (NGO), and SrTiO₃(001) (STO). Due to the lattice mismatch between the films and the substrates ranging from -2.6% to +1%, different strains can be imposed to the films. We have found that: (1) large low-field magnetoresistance(LFMR) behaviours are observed in PSMO, LCMO and LSMO thin films on LAO substrates when a magnetic field is applied perpendicular to the film plane, but the maximum LFMR is the largest in PSMO and LCMO samples; (2) most of the films grown on STO substrates show positive MR when a magnetic field is applied perpendicular to the film plane, and when the field is parallel to the film plane all films show negative MR regardless of the substrates; (3) the large low-field MR is strongly dependent on the film thickness and the composition of the manganites. The anomalous low-field MR effect will be discussed based on strain-induced magnetic anisotropy and domain rotation and movement.