Effect of small quantity of chromium on the electrical, magnetic and magnetocaloric properties of Pr0.7Ca0.3Mn0.98Cr0.02O3 manganite

Abstract

Structural, electrical and thermomagnetic properties of Pr0.7Ca0.3Mn0.98Cr0.02O3 were investigated. Sample was prepared by solid-state reaction method. X-ray diffraction revealed that the sample crystallizes in the orthorhombic system with Pnma space group. Electrical conductivity and complex impedance studies of Pr0.7Ca0.3Mn0.98Cr0.02O3 system are analyzed. The investigated compound exhibits a semiconductor behavior in the whole explored temperature range. From 100 to 206 K, the increase in DC conductance is more than two decade. At higher temperatures, the conductance varies slowly and a saturation region appears. The conduction mechanism is found to be governed by small polaron hopping process which is explained by the short range thermally activated energy. Conductance spectrum is well described by Jonsher law, and the temperature dependence of the frequency exponent confirms that conduction mechanism is governed by hopping process of the localized carriers. Using complex impedance analysis, the compound is modeled by an electrical equivalent circuit. Also, such analysis confirms the contribution of grain boundary to the transport properties. The substitution of Mn by 2 % Cr destroyed the charge order state observed in the parent compound and induced a ferromagnetic phase at low temperatures. For a magnetic field change of 5 T, the material shows a maximum magnetic entropy change |∆S max| = 2.69 J kg−1 K−1 with a full width at half maximum δ TFWHM = 145 K, and a relative cooling power RCP = 389 J kg−1. Pr0.7Ca0.3Mn0.98Cr0.02O3 material demonstrates potential proprieties to be used in electronic and thermal devices and as magnetic refrigerant.