Surface magnetic ripples induced by a local magnetic field from a scanning magnetic tip

When demagnetized La 1-xSrxMnO3 (LSMO) thin films are magnetized by a local magnetic field from a scanning magnetic tip without an external magnetic field, a mangetic ripple pattern appears on the LSMO surface. The magnetic ripple pattern, consisting of magnetic ripples with varying magnetic periods, is different from the conventional pattern magnetized by an external field. The magnetic ripples with longer magnetic periods have a larger magnitude of magnetic moment. However, the magnitude of the remanent magnetization induced by the magnetic force microscopy (MFM) tip is close to that induced by the external field. Since the MFM images of the magnetic ripples with varying periods can be converted to inverse images and spectra by a fast Fourier transformation (FFT), the inverse FFT images and spectra are also used to probe the magnitude of magnetic moment of the periodic magnetic ripples.