Structural, magnetic and ferroelectric properties of Ho_1-xCa_xMn_1-yCo_yO₃ (x = 0.05, y = 0.05, 0.1)

Polycrystalline Ho_1-xCa_xMn_1-yCo_yO₃ (x = 0.05, y = 0.05, 0.1) samples were synthesized by solid-state reaction route to study the effect of compositional variation on structural, magnetic and ferroelectric properties. From XRD measurement, it is clearly observed that orthorhombic phase stabilizes completely at y = 0.1. Partial substitution of Ca and Co at Ho and Mn site promotes structural distortion in the lattice which is responsible for suppression of hexagonal structure and stabilization of orthorhombic phase. On the other hand, incorporation of Co²⁺ cation into the HMO causes the transformation of John-Teller Mn³⁺ to Mn⁴⁺ ion which is not a John-Teller cation. Higher substitution of Co at Mn site enhances the magnetic property and shifts the transition temperature toward higher value (154 K). FC and ZFC curves become more divergent below 154 K for y = 0.1, indicating the presence of weak ferromagnetism below 154 K. M-H curve at 150 K for y = 0.1 shows a ferromagnetic-like behaviour which confirms our observed M-T data. The ferromagnetism in the sample may arise due to the double-exchange interaction between Mn³⁺ and Mn⁴⁺ ions. Values of remanent polarization and coercive field are observed to be 0.25 μC/cm² and 3.23 kV/cm, respectively. It is quite interesting that substitution of Ca at Ho site and Co at Mn site induced weak ferromagnetism and ferroelectricity in the material. This finding makes the material a potential candidate for future device application. (orig.)