Giant magnetoimpedance and high frequency electrical detection of magnetic transition in La_0.75Sr_0.25MnO₃

Abstract

We show that high frequency electrical transport is an efficient technique for detecting the magnetic transition hidden by the scattering of charges at grain boundaries in colossal magnetoresistive oxides, even in the absence of any external magnetic field. The dc resistivity which shows only a weak anomaly at the Curie temperature in La0.75Sr0.25 MnO3 transforms into abrupt jumps in both resistive (Z′) and reactive (Z″) parts of the ac impedance, Z(f, T, H) = Z′(f, T, H) + jZ″(f, T, H) at higher frequencies (f = 0.1–5 MHz). The anomaly in Z′ and Z″ at TC decreases as much as 19% and 15%, respectively, in a dc magnetic field of H = 65 mT compared with 1% dc magnetoresistance, suggesting a possible giant low-field magnetoimpedance effect which could be exploited for room temperature practical applications. We interpret our observations due to changes in the magnetic penetration depth induced by the spontaneous ordering of spins and by the applied field.

Unusual field dependence of radio frequency magnetoimpedance in La0.67Ba0.33MnO3

“…A substantial increase in ac magnetoresistance was also reported in the radio frequency range (f = 1-10 MHz) by passing rf current directly through the sample [12] or through an inductance coil surrounding a manganite sample [13]. Recently, Barik et al [14] has reported a spectacular increase in the electrical impedance of La 0.75 Sr 0.25 MnO 3 at the Curie temperature in the absence of external magnetic field and a large low field ac magnetoresistance (= 19% for µ 0 H = 65 mT, f = 3 MHz at T = 300 K), by passing radio frequency current directly through the sample. However, a detail investigation of magnetic field dependence of both the components of electrical impedance is currently lacking.…”

“…However, the magnitude of R is enhanced and shows an abrupt jump at T C when the frequency is increased to 5 MHz. The enhanced magnitude of the resistance in the paramagnetic state is due to the normal skin effect and the abrupt increase at T C is attributed to the decrease in the magnetic penetration depth (δ = (2ρ/ωµ t )) resulting from the rapid increase in the transverse permeability (µ t ) [14]. The ac inductive reactance (X) shown in fig.…”