Enhanced Low-Field Magnetoresistance in La_0.71Sr_0.29MnO₃ Nanoparticles Synthesized by the Nonaqueous Sol–Gel Route

In colossal magnetoresistive (CMR) materials, magnetic fields of several tesla are typically required to exhibit large changes in electrical resistance, and hence, materials should be engineered to provide a more sensitive MR response at lower fields for their viability in practical applications. Enhanced low-field magnetoresistance (LFMR) was observed in highly ferromagnetic ∼20 nm La 0.71 Sr 0.29 MnO 3 particles synthesized by the nonaqueous sol–gel route. The enhanced LFMR of the nanoparticles (NPs) reaches 29.8% at 30 K with 50 mT, and the high-field magnetoresistance was 56% with a 5000 mT applied field. The large LFMR effect can be attributed to the spin-polarized tunneling across the ∼1.3 nm thick natural grain boundaries. The weaker MR effect below 30 K was attributed to the re-entrant spin glass at the core of the NPs and surface spin glass phase that could be eliminated with lower and higher applied fields, respectively. The magnetic and MR properties of the NPs were compared to those of the corresponding ∼2 μm bulk material with the same elemental composition. These results provide insight into the role of particle size, grain boundaries, and spin glass phases on the MR properties, and the consequence of this finding is useful for the potential fabrication of LFMR devices.