Abstract
Cr doping in charge-ordered Pr0.75Na0.25Mn1-xCrxO3 and Nd0.75Na0.25Mn1-yCryO3 have been synthesized using conventional solid-state method to investigate its effect on structural, electrical transport and magnetic properties. X-ray diffraction (XRD) analysis for both compounds showed that the samples were crystallized in an orthorhombic structure with Pnma group. The unit cell volume value decrease as the Cr-doped increased indicating the possibility of Mn3+ ion was replaced by Cr3+ due to the different of ionic radius. The temperature dependence of electrical resistivity showed an insulating behavior down to the lower temperature the both parent compound (x = 0 and y = 0). Successive substitution of Cr at Mn-site in Pr0.75Na0.25Mn1-xCrxO3 manganites induced the metal-insulator (MI) transition temperature around TMI~120 K and TMI~122 K for x = 0.02 and x = 0.04 samples respectively suggestively due to the enhancement of double-exchange (DE) mechanism as a result of suppress the CO state. Analysis of resistivity data of dlnρ/dT-1 vs. T in Nd0.75Na0.25Mn1-yCryO3 manganite, showed a peak around 210 K and 160 K for y = 0 and 0.02 samples respectively while no peak was observed for y = 0.05 sample indicate the charge-ordered (CO) weakened. AC susceptibility, χ’ measurements in Pr0.75Na0.25Mn1-xCrxO3 exhibits paramagnetic to ferromagnetic-like with curie temperature, TC increases from 132 K for x = 0.02 to 141 K for x = 0.04 with Cr content indicate the suppression of CO state meanwhile in Nd0.75Na0.25Mn1-yCryO3 showed paramagnetic to anti-ferromagnetic transition as Neel temperature TN increases from 115 K for y = 0.02 to 125 K for y = 0.05.
Highlights
The discovery of colossal magnetoresistance (CMR) effect in rareearth perovskite-type manganites with general composition of type Re1-xAxMnO3 (Re = a trivalent rare-earth ion, A = a divalent alkaline-earth) have attracted much attention in these recent years [1,2,3,4,5,6,7]. Studies on these rare-earth manganites have revealed that CMR effect which is commonly attributed to the double- exchange (DE) mechanism is suggested to be related to the Jahn-Teller (JT) effect and charge ordering (CO) [8] and the lattice distortion [9]
Analysis of dln /dT-1 vs. T curve displays a peak which indicates CO state for sample y = 0 and 0.02 with a CO transition temperature TCO around 210 K and 160 K respectively while no peak was observed for y = 0.05 sample
By the X-ray diffraction (XRD) analysis for all samples, it is observed that Cr3+ could continuously replace Mn3+ based on the values of calculated unit cell volume, V decrease continuously for both compound with Cr content suggestively due to the Cr3+ ion has a smaller ionic radius compare to Mn3+ ion
Summary
It is reported that among the different studied doping elements, Cr is the most efficient one to induce a metal insulator transition in the CO undoped insulators and leads to a much higher. La0.7Ca0.3Mn1-xCrxO3 the electrical transport behaviour shows that the metal-insulator (MI) transition shift to lower temperature and weakened gradually as the Cr content increased due to DE mechanism between Mn3+–O–Mn4+ [17]. When doping on Mn sites with Cr3+ ions, the transport and magnetic properties of the manganites will show some interesting behaviors. Nd0.75Na0.25MnO3 and the effect of Cr doped in monovalent manganite of Pr0.75Na0.25MnO3 have not been reported yet on structural, transport and magnetic properties. Mn site on the structural, electrical transport and magnetic properties of Pr0.75Na0.25MnO3 and Nd0.75Na0.25MnO3 manganite.
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