Effect of tolerance factor and local distortion on magnetic properties of the perovskite manganites

Abstract

The substitutions of rare earths for La on the magnetic properties of the perovskites ${\mathrm{La}}_{\text{0.7−x}}{\mathrm{R}}_x{\mathrm{A}}_{\mathrm{0.3}}{\mathrm{MnO}}_{\mathrm{3}}$ $\text{(0<x<0.7),}$ $\mathrm{R=Pr}$ or Gd and $\mathrm{A=Ca},$ Sr, or Ba have shown that small substitution of Pr slightly increases the coercive field $H_c$ and magnetization M, and strongly improves the magnetoresistance (MR) while lowering $T_c.$ On the other hand, the substitution of Gd lowers $H_c,$ M and $T_c,$ however, increases MR of the system ${\mathrm{La}}_{\text{0.7−x}}{\mathrm{Gd}}_x{\mathrm{Sr}}_{\mathrm{0.3}}{\mathrm{MnO}}_{\mathrm{3}}$ at temperature ${\mathrm{<T}}_c.$ Large differences in the A-site ionic radii $r_A$ of the ${\mathrm{AMnO}}_{\mathrm{3}}$ perovskites proved detrimental. The optimal composition has been discussed for the half-metallic ferromagnet of a spin-switch device based on the manganese oxides.