Experimental evidence of paramagnons within the glass phase of Ca(Fe1/2Nb1/2)O3

Abstract

The Pb-free complex perovskite Ca(Fe_1/2Nb_1/2)O₃ is a promising material for technological applications, featuring a nearly temperature-independent large dielectric constant over a broad range of temperatures and frequencies. This study explores the structure and low temperature dynamics of this system using multiple experimental techniques. X-ray diffraction analysis confirms the formation of a single-phase sample with an orthorhombic crystal structure in the Pbnm space group, which remains stable down to 12 K. DC susceptibility measurements reveal a bifurcation between zero-field-cooled warming and field-cooled warming curves at the irreversibility temperature (T_irr ≈ 27 K), with a peak at the freezing temperature (T_f ≈ 25 K), indicating glassy dynamics. Specific heat analysis reveals that below T_f, paramagnons co-exist with the glassy phase, whereas above T_f, the system follows the paramagnon model. This study provides new insights into the low-temperature dynamics of Pb-free complex perovskites of the form A(Fe_1/2B_1/2)O₃, where A = Ca, Sr, or Ba, and B = Nb, Ta, or Sb.