Non-Griffiths-like cluster formation in the double-perovskite <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Gd</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>CoMnO</mml:mi><mml:mn>6</mml:mn></mml:msub></mml:mrow></mml:math>: Evidence from critical behavior
Moumita Das, P. Sarkar, P. Mandal
Abstract
We have shown that ferromagnetic double perovskite ${\mathrm{Gd}}_{2}{\mathrm{CoMnO}}_{6}$ 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 $\ensuremath{\delta}$. However, the critical exponent $\ensuremath{\delta}$ for ${\mathrm{Gd}}_{2}{\mathrm{CoMnO}}_{6}$, determined from magnetization scaling analysis, comes out to be very small ($\ensuremath{\delta}=1.55\ifmmode\pm\else\textpm\fi{}0.03$). The small value of $\ensuremath{\delta}$ 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 $\ensuremath{\beta}$ ($=1.18\ifmmode\pm\else\textpm\fi{}0.06$), $\ensuremath{\gamma}$ ($=0.65\ifmmode\pm\else\textpm\fi{}0.01$), and $\ensuremath{\delta}$ 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.