A comparative study on effects of magnesium substitution at Nd and Fe-sites on the structural, optical, magnetic, and dielectric properties of neodymium orthoferrite

• Two series Mg-substituted NdFeO 3 (Nd 1-x Mg x FeO 3 and NdFe 1-y Mg y O 3 , 0 ≤ x, y ≤ 0.2) nanoparticles was synthesized by the sol–gel method. • The band gap dependence on Mg concentration in these compounds is correlated strongly with oxygen vacancy. • Nd 1-x Mg x FeO 3 nanoparticles show a drastic enhancement in the magnetization with soft magnetic behavior suggesting the ferromagnetic nature. • Coercivity force in NdFe 1-y Mg y O 3 nanoparticles increases significantly and reach 1300 Oe. • Neel temperature variations in studied samples was ascribed to the competition of ferromagnetic and antiferromagnetic exchange interactions. Tailoring optical, electrical and magnetic behaviour of orthoferrites is vital for their application in advanced devices. In this study comparatively investigated the effects of magnesium ion substitution on structural, optical, magnetic, and dielectric properties of Nd 1-x Mg x FeO 3 and NdFe 1-y Mg y O 3 (x, y = 0.0, 0.05, 0.10, 0.15, and 0.20). X-ray photoelectron spectroscopy analysis revealed that Mg doping at the Fe site induces a higher concentration of oxygen vacancies compared to that of Nd-site. Rietveld refinement and XRD patterns confirmed that the samples crystalized in an orthorhombic structure with space group Pbnm . The unit cell volume ( V ) decreases overall due to magnesium doping in the Nd and Fe-sites. The FE-SEM images revealed homogenous, spherical nanoparticles ranging in size from 70 nm to 108 nm, depending on the Mg concentration. The optical band gap energy ( E g ) was investigated by diffuse reflectance spectroscopy analysis. While E g decreases from 2.15 eV for the pure sample to 1.87 eV for the y = 0 sample, in Nd 1-x Mg x FeO 3 samples is found to decrease at first until x = 0.10 sample, and then increase monotonically with increasing Mg content. The nature of the magnetic hysteresis loops for Nd 1-x Mg x FeO 3 compounds show a soft ferromagnetic behavior. Notably, the remanent magnetization in the Nd 1-x Mg x FeO 3 samples was found to be more than five times higher than that of the NdFe 1-y Mg y O 3 compounds. By contrast, H c in NdFe 1-y Mg y O 3 nanoparticles increases significantly from y > 0.05 and reaches 1300 Oe for the sample with y = 0.2 while the H c decreases slightly with Mg doping in Nd 1-x Mg x FeO 3 samples. A substantial increase in the dielectric constant was observed in all the Mg-substituted samples at room temperature, regardless of the substitution site. However, this increase was considerably more pronounced in the samples in which Mg was substituted at the Fe-site. Finally, the presence of an anomaly in the temperature dependence of the dielectric constant for the studied samples around the antiferromagnetic-paramagnetic transition implies the existence of magnetoelectric coupling in our compounds due to strong spin-phonon coupling