Suppression of charge order and antiferromagnetic to ferromagnetic switchover in Nd_0.5 Ca_0.5 MnO_3 nanoparticles

TL;DR

This study investigates how reducing the size of Nd_0.5 Ca_0.5 MnO_3 nanoparticles suppresses charge order and antiferromagnetism, inducing a ferromagnetic transition and metal-insulator transition at nanoscale.

Contribution

It demonstrates size-dependent magnetic and electronic phase transitions in Nd_0.5 Ca_0.5 MnO_3 nanoparticles, revealing suppression of charge order and antiferromagnetism at small sizes.

Findings

20 nm particles lack charge order and antiferromagnetism

Ferromagnetic transition at 95 K in 20 nm particles

Magnetization increases as particle size decreases

Abstract

Nd_0.5 Ca_0.5 MnO_3 (NCMO) nanoparticles (average diameter ~ 20 and 40 nm) are synthesized by polymeric precursor sol-gel method and characterized by X- ray diffraction, transmission electron microscopy (TEM), selective area electron diffraction (SAED), superconducting quantum interference device (SQUID) magnetometery and resistivity measurements. Both single crystalline and polycrystalline particles are present in the samples and they are found to retain the orthorhombic structure of the bulk NCMO. However, most strikingly, in the 20 nm particles, the charge ordered (CO) and the antiferromagnetic phases observed in the bulk at 250 K and 160 K respectively are completely absent. Instead, a ferromagnetic (FM) transition is observed at 95 K followed by an insulator to metal transition at 75 K. In the 40 nm particles, though a weak, residual CO phase is observed, transition to FM state also occurs, but at a slightly higher temperature of 110 K. The magnetization is found to increase with the decrease of particle size.