Non-Griffiths-like cluster formation in the double-perovskite Gd₂CoMnO₆ : Evidence from critical behavior

Abstract

We have shown that ferromagnetic double perovskite Gd₂CoMnO₆ exhibits the characteristics of clustered phase, which are quite different from that of Griffiths phase observed in several perovskite compounds. The Yang-Lee theory of phase transition predicts that the essential singularity of the Griffiths phase leads to very unusual critical phenomena, including a discontinuity in the magnetization isotherm at T=T_C, which is reflected through the large value of critical exponent δ. However, the critical exponent δ for Gd₂CoMnO₆, determined from magnetization scaling analysis, comes out to be very small (δ=1.55±0.03). The small value of δ suggests that the continuous ordering is slow, indicating non-Griffiths-like cluster formation in the studied system, which is further supported by the evolution of susceptibility with temperature and magnetic field. Also, the observed values of all the three exponents β (=1.18±0.06), γ (=0.65±0.01), and δ are far from any existing universality class and they deviate from the mean-field values in the opposite direction to that for the conventional universality.