Electron Magnetic Resonance Studies of Nanosized Nd0.65Ca0.35 Mn1−xCrxO3 (x = 0, 0.06, 0.1) Manganite

Abstract

We report a systematic investigation of the temperature dependence of electron magnetic resonance (EMR) line width, intensity and resonance field for ~25 nm Nd0.65Ca0.35MnO3 (NCMO1), Nd0.65Ca0.35Mn0.94Cr0.06O3 (NCMO2) and Nd0.65Ca0.35Mn0.9Cr0.1O3 (NCMO3) nanoparticles prepared by sol–gel method. The EMR line widths for the three nano-samples differ significantly from one another below a temperature T min where the line width has a minimum. T min was found to be 130, 100 and 120 K for NCMO1, NCMO2 and NCMO3, respectively. Well above T min the line width values for the three samples are close to one another. The sharp upturn of EMR line width below T min is attributed to the formation of short range, ferromagnetically ordered clusters. Temperature dependence of EMR intensity shows a residual CO transition in NCMO1 and NCMO2 and a complete disappearance of it in NCMO3. The intensity undergoes significant increase below 120, 80 and 100 K for NCMO1, NCMO2 and NCMO3, respectively, indicating the onset of ferromagnetic transitions. The occurrence of ferromagnetic transition is further confirmed by magnetization hysteresis measurements. The decrease in T C in NCMO2 and NCMO3 compared to NCMO1 nanoparticles is understood to be due to the destruction of the double-exchange interaction by chromium doping. The resonance field decreases below the ferromagnetic onset temperatures for all the samples as expected. The combined effects of the reduction in size and of chromium doping in Mn site are discussed.