Particle Size Effects on Charge and Spin Correlations in Nd_0.5Ca_0.5MnO₃ Nanoparticles

Abstract

The particle size effects on the charge and spin correlations in half-doped manganite Nd0.5Ca0.5MnO3, which exhibits a charge-ordered (CO) transition at 250 K in the bulk counterpart, have been investigated by magnetometry and electron spin resonance (ESR). Magnetic measurements show that reducing the particle size weakens the long-range CO transition, which completely disappears when the particle size is reduced down to 40 nm. Meanwhile, a weak ferromagnetic (FM) behavior appears at low temperatures and is gradually enhanced with the decrease of the particle size. The ESR intensities of the nanoparticles reproduce well these features. However, the temperature dependences of the ESR g-factor and line width exhibit the typical characteristics of the CO states in all the nanoparticles, even in the 40 nm sample, which suggests that, even though the long-range CO transition is completely suppressed by the size reduction, the CO state is still present in the short-range ordering form. Moreover, it is found that the onset temperatures of the CO states in all the nanoparticles are almost the same as that of the bulk, which strongly indicates that the strength of the CO correlations in this compound is not influenced much by the particle size. A detailed analysis on the magnetic susceptibilities and the ESR line width further reveals that both the antiferromagnetic (AFM) and the FM spin interactions are weakened by the size reduction, which suggests that the enhanced FM behavior in the nanoparticles is not due to the enhancement of the double-exchange FM interactions. We propose that, although the FM interactions are weakened, they gradually dominate over the AFM ones at low temperatures with the decrease of the particle size due to the more significant weakening of the latter by the size reduction, which, hence, gives rise to the development of the FM behaviors in the nanoparticles.

Direct experimental evidence of multiferroicity in a nanocrystalline Zener polaron ordered manganite

“…There is a realistic possibility that a short-range charge-ordered state might exist when the long-range one is destroyed by the size reduction as observed before in the half-doped manganite nanoparticles 38,39 . Admittedly since charge ordering gets progressively weaker as one moves away from half-doping, one might expect complete suppression of even short range correlation below a certain critical size of the nanoparticle.…”

“…This results in weakening of the charge-ordering and its eventual collapse 2) spin-canting in the anti-ferromagnetic (AFM) structure due to exchange biasing with surface spin configuration leading to weakening of charge order, etc. Interestingly, there are a few studies which claim that even though long range charge ordering is destroyed with particle size reduction, short range correlation persists 38,39 . All these plausible scenarios which lead to suppression of long range charge ordering can actually be bracketed under two major categories related to the general consequences of particle size reduction in any crystal: first, the surface and interface effects due to enhanced surface to volume ratio and second, the changes in lattice symmetry.…”

Charge order and antiferromagnetism in epitaxial ultrathin films ofEuNiO3

“…In particular, electric field induced changes in the CO state, where the modulated charge density acquires a periodic pattern typically leading to insulating behavior has received wide attention lately and been implemented in several devices [5][6][7][8][9][10][11] . In the ferrites, for instance, the application of an external electric field was found to induce a phase transition to a metallic state with a resistance change of several orders of magnitude, allowing their incorporation into devices [9][10][11] .…”

“…In ENO, despite the ultra thin geometry and altered electronic bandwidth, our findings revealed that the CO and AFM transitions remain bulk-like. Moreover, CO is observed at room temperature rendering ultra-thin ENO films and heterojunctions potential use for novel electric field controlled devices along with CMR manganites and ferrites [5][6][7][8][9][10][11] .…”

Detection of low ppm carbon monoxide with charge ordered LuFe 2 O 4 gas sensor – A novel sensing mechanism

“…Additionally, we assessed the structural features of the synthesized LFO system through microscopic images, as charge order is known to be suppressed for smaller nanoparticles and is generally absent for particles with dimension below 35 nm [19,20].…”