Evidence of Griffiths Phase and Antiferromagnetic State in Bi-Doped LaMnO$_{3}$

Abstract

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.