Correlation between magnetoimpedance and permeability in La 2/3Ba 1/3MnO 3

Abstract

Even though the dc magnetoresistance Δ ρ/ ρ 0 is only −4.2% under 8 kOe, La 2/3Ba 1/3MnO 3 manganite sintered at 1280 °C could present a huge ac magnetoresistance Δ R/ R 0=−43.3% at 10 MHz, a large magnetoreactance Δ X/ X 0=−37.3% at 200 kHz and a giant magnetoimpedance Δ Z/ Z 0=−30% at 4 MHz under a low field H=600 Oe at room temperature. There is a correlation between giant magnetoimpedance effect and permeability change. Both resistance R and circular imaginary permeability μ ϕ ″ decrease with an increase of field at frequencies f≤30 MHz. The reactance X decreases with increasing field at frequencies f≤20 MHz, meanwhile the circular real permeability μ ϕ ′ monotonically drops. At a high frequency of 30 MHz, both X and μ ϕ ′ experience a small peak with an increase of field. With an increase of ac frequency, under a field of 600 Oe the magnetoresistance Δ R/ R 0 increases at first, undergoes a maximum at 10 MHz, and then drops, while magnetoreactance Δ X/ X 0 shows an almost monotonous decrease at frequencies above 1 MHz. Correspondingly, the change of circular imaginary permeability Δ μ ϕ ″ / μ ϕ ″ ( 0 ) under 600 Oe undergoes a maximum of −92.6% at 4 MHz and then drops with frequency, while the change of circular real permeability Δ μ ϕ ′ / μ ϕ ′ ( 0 ) drops monotonically from −67.9% at 500 kHz to −11.7% at 30 MHz. The magnetoresistance is mainly dominated by the change of transverse imaginary permeability, while the magnetoreactance is mainly controlled by the change of transverse real permeability.