Unusual electrical behaviour in sol–gel-synthesised PKMO nano-sized manganite

Abstract

Mixed-valence manganites have gained tremendous attention in the scientific research for its colossal magnetoresistance phenomenon. Nevertheless, the study devoted to praseodymiumbased manganites is still limited to date. The present work aims to investigate the grain size effect on sol-gel grown nano-sized Pr0.85K0.15MnO3 (PKMO). The grain size has been modified by heat treatment ranging from 600 °C to 1000 °C. PKMO samples have been studied in detail to elucidate the correlation of spin, charge, orbital and lattice degrees of freedom. The X-ray diffraction analysis revealed that all samples exhibit in single orthorhombic phase with the space group of Pnma (62). The obtained crystallite size and average grain size are in the range of 45-115 nm and 51-210 nm, respectively. The evolution of grains intensively affects the electrical and magneto-transport properties of PKMO. The temperature dependence of the resistivity has been fitted with theoretical expressions in different temperature regimes to investigate their conduction mechanisms. The resistivity exhibits an unusual trend when the grain size increases where a similar pattern also been observed in metal-insulator transition temperature (TMI). This behaviour can be ascribed to the grain size distribution, grain formation and also the occurrence of oxygen vacancies at the grain boundaries. Enhancement of high field magnetoresistance has been discovered below 180 K, whereas low field magnetoresistance is suppressed as the temperature increases and almost vanished at 300 K. The PKMO study demonstrated here is clearly dominated by extrinsic properties (grain evolution) from the evidence of electrical and magneto-transport measurements.

The Physical Properties of Submicron and Nano-Grained La0.7Sr0.3MnO3 and Nd0.7Sr0.3MnO3 Synthesised by Sol–Gel and Solid-State Reaction Methods

“…Enhancement of LFMR was observed in LSSG and NSSG, as shown in Figure 7a. Moreover, NSSS recorded the highest MR (27.7%) near the TMI and this is attributed to the increase in disordered magnetic spin fluctuations at the high-temperature range [35]. Therefore, we can conclude that NSSS is dominated by intrinsic MR accompanied by weak extrinsic MR. samples at 0.2 and 1 T. The MR of LSMO increases monotonically with the decrease in temperature and it is comparable with the results reported earlier [42,56].…”

“…The grain and crystallite sizes will be increased with the sintering temperature due to the congregation effect [20]. However, single-crystallite grains can be formed when samples are sintered at low temperatures [35] and this was witnessed in our NSSG sample. Furthermore, LSSG was found to have two crystallites in a single grain when referring to the data given in Table 2.…”

“…The samples will hereafter be denoted as LSSG, LSSS, NSSG, and NSSS. A similar sol-gel preparation procedure has been reported in our previous works [20,35]. The stoichiometric amounts of La (NO 3 ) 3 •6H 2 O (Alfa Aesar, Heysham, UK; 99.99%), N 2 O 6 Sr (Alfa Aesar, Heysham, UK; 99.97%), and Mn (NO 3 ) 2 •4H 2 O (Sigma-Aldrich, St. Louis, MO, USA; ≥97%) were used as the precursors to synthesise LSSG.…”

Current-dependent positive magnetoresistance in La0.8Ba0.2MnO3 ultrathin films*

“…In previous work, the effects of grain size on the electrical and magnetic properties of manganites have been reported by many authors. [23][24][25] Dey et al observed a gradual drop of the MIT temperature with a decrease in the grain size, while the ferromagnetic-paramagnetic transition temperature remained almost unchanged in their granular La 0.7 Ca 0.3 MnO 3 samples. [23] Here, we consider the grain size effect to be the reason for the much lower T P in the 6 nm-thick film.…”

Structural and Morphology Changes in PrMnO3 Manganite Induced by Ba (x=0.33) Doping

“…This distortion of MnO6 octahedra leads to the localisation of electrons. In fact, a significant defect in the A-site cations results in a random arrangement of the Mn 3+ and Mn 4+ ions [22,23]. According to the morphology, the average diameter of Pr0.67Ba0.33MnO3 is 2.312 μm by using the scale of 20 μm in Figure 4.…”