Effects of grain size on reversible and irreversible domain wall displacements in La_(0.7)Sr_(0.3)MnO_3 perovskite

摘要

In this work, the permeability spectra of La_(0.7)Sr_(0.3)MnO_3 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 (μ_e) decreases from 87 to 11 with D, while relaxation frequency f_r increases from 205 kHz to 231 MHz. As the amplitude of the ac field h_o exceeds the domain wall pinning field h_p, irreversible domain wall motions will be activated. The increments of permeability with increasing h_o can be explained using the Rayleigh law. With reducing D from 1200 to 140 nm, h 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 μ_e and f_r has been discussed related to the demagnetizing field induced by distributed air gaps between grains.