Realizing the ‘hindered charge ordered Phase’ in nanoscale charge ordered manganites: magnetization, magneto-transport and EPR investigations

摘要

We report three prominent observations made on the nanoscale charge ordered (CO) manganites RE_(1-x)AE_xMnO_3 (RE = Nd, Pr; AE = Ca; x = 0.5) probed by temperature dependent magnetization and magneto-transport, coupled with electron magnetic/paramagnetic resonance spectroscopy (EMR/EPR). First, evidence is presented to show that the predominant ground state magnetic phase in nanoscale CO manganites is ferromagnetic and it coexists with a residual anti-ferromagnetic phase. Secondly, the shallow minimum in the temperature dependence of the EPR linewidth shows the presence of a charge ordered phase in nanoscale manganites which was shown to be absent from the DC static magnetization and transport measurements. Thirdly, the EPR linewidth, reflective of spin dynamics, increases significantly with a decrease of particle size in CO manganites. We discuss the interesting observations made on various samples of different particle sizes and give possible explanations. We have shown that EMR spectroscopy is a highly useful technique to probe the `hindered charge ordered phase' in nanoscale CO manganites, which is not possible by static DC magnetization and transport measurements.