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

The substitutions of rare earths for La on the magnetic properties of the p erovskites La(0.7-x)R(x)A(0.3)MnO(3) (0 < x < 0.7), R=Pr or Gd and A=Ca, Sr , or Ba have shown that small substitution of Pr slightly increases the coe rcive field H-c and magnetization M, and strongly improves the magnetoresis tance (MR) while lowering T-c. On the other hand, the substitution of Gd lo wers H-c, M and T-c, however, increases MR of the system La0.7-xGdxSr0.3MnO 3 at temperature < T-c. Large differences in the A-site ionic radii r(A) of the AMnO(3) perovskites proved detrimental. The optimal composition has be en discussed for the half-metallic ferromagnet of a spin-switch device base d on the manganese oxides. (C) 1999 American Institute of Physics. [S0003-6 951(99)02634-0].