Effects of grain size on reversible and irreversible domain wall displacements in La0.7Sr0.3MnO3 perovskite

In this work, the permeability spectra of La0.7Sr0.3MnO3 perovskite with mean grain size (D) ranging from 1200 to 45 nm have been investigated at 293 K. The spectra exhibit a typical relaxation, relating to reversible domain wall motions. The quasi-static permeability (μe) decreases from 87 to 11 with D, while relaxation frequency fr increases from 205 kHz to 231 MHz. As the amplitude of the ac field h0 exceeds the domain wall pinning field hp, irreversible domain wall motions will be activated. The increments of permeability with increasing h0 can be explained using the Rayleigh law. With reducing D from 1200 to 140 nm, hp increases from 1.8 to 2.3 A/m and the Rayleigh constant decreasing from 2.15 x 10-1 to 4.66 x 10-2 (A/m)-1. The grain size dependence of μe and fr has been discussed related to the demagnetizing field induced by distributed air gaps between grains. (copyright 2005 WILEY-VCH Verlag GmbH and Co. KGaA, Weinheim) (orig.)