Electrical, magnetic, and magnetoresistance studies in chromium-doped Pr-based manganites

The effect of Cr 3+ on the electrical, magnetic and magnetoresistance effect in Pr 0.75 Na 0.05 K 0.2 Mn 1− x Cr x O 3 ( 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 Å 3 ( x = 0) to 231.25 Å 3 ( x = 0.01) suggesting that substitution with a low concentration of Cr 3+ may predominately substitute for Mn 4+ site. However, further substituting Cr 3+ caused a decrease in unit cell volume from 231.15 Å 3 ( x = 0.02) to 227.74 Å 3 ( x = 0.05), indicating at high concentration of Cr 3+ dominantly substituted the Mn 3+ . Cr 3+ substitution slightly decreased the Curie temperature ( T C ) 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 Cr 3+ slightly disturb ferromagnetic (FM) interaction between Mn 3+ –O 2− –Mn 4+ . Interestingly, further substitution of Cr 3+ increased the T C 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 Cr 3+ and Mn 3+ ions due to the similar electronic configuration of Cr 3+ with that of Mn 4+ ions. The observed large increased in resistivity with Cr 3+ substitution and the decrease in metal insulator transition temperature ( T MI ) 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 Mn 3+ –O 2− –Mn 4+ , Cr 3+ –O 2− –Mn 3+ , Cr 3+ –O 2− –Cr 3+ , Cr 3+ –O 2− –Mn 4+ . 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.