Title : Interplay of charge transport and magnetism in Pr₀.₅₋ₓNaₓSr₀.₅MnO₃ (x = 0, 0.5)
Abstract:
The present study investigates the structural, electrical, and magnetic properties of half-doped perovskite manganites with the general formula Pr?.???Na?Sr?.?MnO? (x = 0, 0.05). These materials are of significant interest due to the strong coupling among charge, orbital, spin, and lattice degrees of freedom, which give rise to a wide variety of intriguing physical phenomena. The substitution of a monovalent cation such as Na? at the A-site of the perovskite lattice is expected to alter the Mn³?/Mn?? ratio, thereby tuning the delicate balance between competing magnetic and electronic interactions. To explore these effects, polycrystalline samples were synthesized using the conventional solid-state reaction method, where NaF was employed as a flux material to compensate for the volatility of sodium and to achieve better phase purity.
X-ray diffraction patterns analyzed through Rietveld refinement confirmed that the parent compound Pr?.?Sr?.?MnO? (PSM0) crystallizes in a tetragonal structure with the I4/mcm space group, consistent with earlier reports. In contrast, the Na-doped sample Pr?.??Na?.??Sr?.?MnO? (PSM5) exhibited additional diffraction peaks corresponding to a minor secondary phase of hexagonal SrMnO?. The emergence of this secondary phase suggests partial incorporation of Na into the lattice and possible modification of oxygen stoichiometry during synthesis. The overall structural analysis indicates that Na substitution leads to lattice distortion and slight changes in crystallographic parameters, which in turn influence the transport and magnetic properties of the system.
Electrical resistivity measurements were carried out over the temperature range of 5–300 K under applied magnetic fields of 0 and 90 kOe using a four-probe configuration. In the undoped sample (PSM0), a pronounced transition from the ferromagnetic metallic (FMM) to the antiferromagnetic insulating (AFI) phase was observed, accompanied by a clear thermal hysteresis between cooling and warming cycles, characteristic of a first-order transition. The application of a magnetic field was found to suppress the charge ordering (CO) behavior, indicating strong field dependence of the electronic phase. In contrast, the Na-doped sample (PSM5) showed a complete suppression of charge ordering and the absence of any first-order transition. Instead, it displayed a smooth transition from a paramagnetic insulating (PMI) to a ferromagnetic metallic (FMM) phase, without noticeable hysteresis.
Magnetization studies further confirmed these findings, with PSM0 showing a sharp drop in magnetization near the Néel temperature (~158 K) due to the FMM–AFI transition, whereas PSM5 exhibited only a paramagnetic–ferromagnetic transition. The results collectively indicate that Na substitution at the Pr site effectively destroys the charge ordering state and enhances the ferromagnetic metallic behavior, mainly due to the increased Mn?? concentration and strengthened double-exchange interactions.
These findings provide valuable insights into the interplay of charge transport and magnetism in half-doped manganites and highlight the potential of Na substitution as a route to tune their functional properties for magneto resistive and energy storage applications.
