Huge ac magnetoresistance of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ in sub-kilogauss magnetic fields

We report radio frequency (f = 0.1 5 MHz) magnetotransport of La$_{0.7}$Sr$_{0.3}$MnO$_{3}$ in sub kilogauss magnetic fields (H = 0-1 kG). We measured ac resistance (R) and reactance (X) simultaneously. In zero field, R decreases smoothly around the Curie temperature $T_{C}$ when $f$ = 100 kHz, but it increases abruptly and shows a peak close to T$_{C}$ for $f $= 0.5-5 MHz. The peak decreases in amplitude, broadens and shifts downward in temperature as the bias field increases. The peak is completely suppressed under $H_{dc}$ = 1 kOe when $f $= 0.5 MHz. A huge low-field \textit{ac} magnetoresistance ($\Delta R$/$R$ = 40 {\%}) and magnetoinductance ($\Delta $X/X = 12 {\%}) are found in a field of $H_{dc}$ = 700 Oe and $f $= 2 MHz. We suggest that the observed ac magnetoresistance arises from the suppression of ac permeability and enhanced magnetic skin depth under a magnetic field. The dynamical magnetotransport reported here will be interesting from view points of fundamental physics and applications.