Influence of Gd Doping at A Site upon the Magnetic Structure of La_(0.7-x)Gd_xSr_(0.3)MnO_3 System

M-T curves, M-H curves, and electron-spin-resonance spectra (ESR) of La0.7-xGdx-Sr0.3MnO3(0.0≤x≤0.70) were investigated. The experimental results indicate that the system is in a ferromagnetic long-range order at Gd low-doping level; at x=0.30 and 0.40, the samples show cluster-spin glass behavior; atx≥0.50, the system possesses the antiferromagnetic characters. For the samples 1=0.30 and 0.40, ESR spectra demonstrate that the phase separation occurs at the temperature far above Tc.