Optical, magnetic and magneto-transport properties of Nd 1-xAxMn0.5Fe0.5O3-δ (A=Ca, Sr, Ba; x=0, 0.25)

The effect of A-site doping by alkaline earth metals (A = Ca, Sr and Ba) on optical, magnetic, and electrical properties of Nd(1-x)A(x)Mn(0.5)Fe(0.5)O(3-delta) (x = 0, 0.25) has been investigated. The UV-vis absorption spectra show that the A-site doping decreases the absorption. Two values of optical band-gap energy (E-g) can be estimated for each studied sample: the higher E-g value is associated with the charge transfer involving iron cations and the lower E-g value - with the charge transfer via manganese cations. Partial substitution of neodymium by alkaline earth metals decreases the Neel temperature (T-N) and induces significant irreversibility between the zero-field cooled (ZFC) and field-cooled (FC) data below T-N. The field-dependent magnetization at 3 K indicates antiferromagnetic ordering with a spin canting. Temperature dependencies of resistivity demonstrate the change from metallic to semiconductor-type conduction (with increasing temperature) at T = T-p < T-N. The T-p temperature significantly decreases with doping. The introduction of alkaline earth metals in Nd(1-x)A(x)Mn(0.5)Fe(0.5)O(3-delta) noticeably reduces the resistivity in the semiconducting region. The small polaron hopping (SPH) mechanism of conduction is suggested at T > T-N. Within the range of T-p < T < T-N, the resistivity data are interpreted by the variable range hopping (VRH) mechanism. A significant value of magnetoresistance (similar to 44%) is observed only for Nd(0.75)Sr(0.25)Mn(0.5)Fe(0.5)O(3-delta )at 120 K. (C) 2020 Elsevier B.V. All rights reserved.