Study of the modified magnetic, dielectric, ferroelectric and optical properties in Ni substituted GdFe 1- x Ni x O 3 orthoferrites.

Polycrystalline GdFe _{1- x} Ni _x O ₃ ( x  = 0.00, 0.02, 0.04) samples was synthesised using a glycine assisted sol-gel method to investigate the enhanced magnetic and electric properties of Ni substituted GdFeO ₃ systems. TG-DSC analysis of prepared samples confirms that GdFe _{1- x} Ni _x O ₃ have good thermal stability in high temperatures. The system has been stabilized in an orthorhombic structure with space group Pbnm . The elemental composition of GdFe _{1- x} Ni _x O ₃ has been estimated from EDAX spectrum. The results showed oxygen deficiency on increasing the Ni substitution and it has been supported by Rietveld refinement. FE-SEM images and Brunauer-Emmett-Teller analysis reveals that GdFe _{1- x} Ni _x O ₃ is a highly porous material and its porosity and specific area increases with Ni substitution. Magnetic measurements indicates that the system exhibited ferrimagnetic behaviour at low temperatures and canted antiferromagnetic behaviour at room temperature. For x  = 0.04 Ni content, magnetization reversal for applied field of 25 Oe has been observed. Increased coercivity of GdFeO ₃ with Ni substitution has been attributed to the grain size effect. From electrical point of view, dielectric permittivity of GdFeO ₃ has been enhanced with Ni substitution. This enhancement has been attributed to the cumulative effects of hopping of Fe ²⁺ -Fe ³⁺ ions, grain-grain boundary contribution, and space charge polarization. The role of grain-grain boundary contribution is evident from electric modulus spectrum. The space charge effect has been realized in both impedance spectrum and dielectric loss. Temperature-dependent dielectric studies were conducted to understand the mechanisms and various aspects that contribute to the dielectric enhancement. A highly lossy capacitive nature in the P - E loop also suggests space charge effects due to Ni substitution in Fe sites. Availability of free charge carrier concentration is correlated with the optical properties of GdFe _{1- x} Ni _x O ₃ . The decrease of optical band gap (2.5-2.21 eV) on increasing Ni content suggests the increasing electronic contribution in the system.
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