| Summary: | The effect of Cr3+ on the electrical, magnetic and magnetoresistance effect in Pr0.75Na0.05K0.2Mn1−xCrxO3 (x = 0.0, 0.01, 0.02, 0.03, 0.04, 0.05) synthesised using the solid-state method are reported. An analysis at room temperature of X-ray diffraction data using the Rietveld refinement method showed all samples crystallised in the orthorhombic phase with Pnma space group. It is found that unit cell volume increased from 230.60 Å3 (x = 0) to 231.25 Å3 (x = 0.01) suggesting that substitution with a low concentration of Cr3+ may predominately substitute for Mn4+ site. However, further substituting Cr3+ caused a decrease in unit cell volume from 231.15 Å3 (x = 0.02) to 227.74 Å3 (x = 0.05), indicating at high concentration of Cr3+ dominantly substituted the Mn3+. Cr3+ substitution slightly decreased the Curie temperature (TC) value from 140.7 K (x = 0.00) to 139.7 K (x = 0.01) and 139.3 K (x = 0.02) indicates the substitution of Cr3+ slightly disturb ferromagnetic (FM) interaction between Mn3+–O2−–Mn4+. Interestingly, further substitution of Cr3+ increased the TC to 140 K (x = 0.03), 140.7 K (x = 0.04) and 143.4 K (x = 0.05) which revealed the possibility of the existence of ferromagnetic interaction between Cr3+ and Mn3+ ions due to the similar electronic configuration of Cr3+ with that of Mn4+ ions. The observed large increased in resistivity with Cr3+ substitution and the decrease in metal insulator transition temperature (TMI) from 122 K (x = 0) to 90 K (x = 0.05) from resistivity versus temperature curve indicates the Cr substitution weakened mechanism and induce more competition between double-exchange (DE) and super-exchange (SE) mechanism involving Mn3+–O2−–Mn4+, Cr3+–O2−–Mn3+, Cr3+–O2−–Cr3+, Cr3+–O2−–Mn4+. The observation large magnetoresistance (MR) effect in Cr-substituted sample at low temperature region indicates enhancement of extrinsic MR effect, which likely arises from spin polarized tunnelling. © The Author(s), under exclusive licence to Springer Science+Business Media, LLC, part of Springer Nature 2024.
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