Evidence of Griffiths Phase and Antiferromagnetic State in Bi-Doped LaMnO_{3}

The magnetic behavior of La\(_{1-x}\)Bi\(_{x}\)MnO\(_{3}\) (\(x = 0.20\), 0.25, 0.30, and 0.40) has been studied, with a Griffiths phase in particular for the sample \(x = 0.4\) with an isovalent Mn\(^{3+}\) for the whole system. The X-ray photoemission spectra (XPS) of each element for all prepared samples of La\(_{1-x}\)Bi\(_{x}\)MnO\(_{3}\) are the same, and have no obvious change due to the Bi ions doping. The Mn 2\(p\) core level XPS shows that the valence state of Mn ion is 3+, and stays in isovalent Mn\(^{3+}\) with increasing doping concentration. Zero-field-cooling and field-cooling curves demonstrate a traditional ferromagnetic to paramagnetic phase transition for all samples, but a special step-like behavior for \(x = 0.4\). For \(x = 0.4\), the Griffiths phase is observed above the Curie temperature\( T_{C}\), which is shown by the evidence of the downturn deviation from the Curie–Weiss linear law and the demonstration of a ferromagnetic cluster revealed by an isothermal magnetization and an Arrott plot. Below \(T_{C}\), an obvious antiferromagnetic state exists with a cusp at a characteristic temperature \(T_{f}\), which is also proved by the non-peak-shift with different frequency in the temperature dependence of the ac-susceptibility.