Low-Field Giant Magnetoimpedance and AC Huge Magnetoresistance for La $_{0.7}$ Sr $_{0.3}$ MnO

The sol-gel La_0.7 Sr_0.3 MnO₃ shows a very small dc magnetoresistance (ΔR/R₀ = -3.5%) under H=10 kOe at room temperature. However, a giant magnetoimpedance (GMI effect) of ΔZ/Z₀ = -21.3% at 100 kHz and a huge ac magnetoresistance of ΔR/R₀ = -52% at 1 MHz could be obtained for La_0.7Sr_0.3MnO₃ sol-gel manganite under a low field of H=500 Oe. For La_0.7Sr_0.3MnO₃ sol-gel manganites, the thicker sample prefers to have a stronger magnetoimpedance at low frequencies. The GMI and huge ac magnetoresistance at frequencies with strong skin effect are mainly connected with the field induced variation of transverse permeability via the penetration depth.