Direct observation of magnetization reversal and low field magnetoresistance of epitaxial La_(0.7)Sr_(0.3)Mn0_3/SrTiO_3 (001) thin films at room temperature

摘要

We have observed the in-plane magnetic domain arrangement during magnetization reversal in a 40 nm thick La_(0.7)Sr_(0.3)Mn0_3/SrTiO_3 (001) thin film patterned into 500μm long microbridges of width 50 or 100/im. Magneto-optical Kerr effect microscopy was used at room temperature and magnetic hysteresis loops were deduced from local averaging of intensity over the microbridge areas. Magnetization reversal proceeds by nucleation and propagation of 180~° domain walls. When the magnetic field was applied parallel to the bridge, we observed the nucleation of only one or two domain walls and the reversal occurred by the propagation of them. When the magnetic field was applied perpendicular to the bridge, the reversal occurred mostly by the nucleation of several domain walls. The low field magnetoresistance (MR) and the low frequency noise at zero magnetic field were measured at room temperature. In addition to the linear and reversible colossal MR effect, hysteretic MR versus magnetic field curves could be observed, showing two maxima (minima) when the magnetic field is parallel (perpendicular) to the bridge length. The observed hysteretic MR behaviour is attributed to anisotropic MR inside the 180° Neel domain walls.