Electron spin resonance study of bulk and nanosized La_(0.875)Sr_(0.125)MnO_3

摘要

The structural, transport and electron spin resonance properties of bulk and nanosized La_(0.875)Sr_(0.125)MnO_3 prepared by a sol-gel method have been investigated. The bulk sample has an orthorhombic structure and a ferromagnetic insulating ground state. The ESR spectra indicate the coexistence of the ferromagnetic insulating and ferromagnetic metallic phases below T_C; In addition to a sharp peak in the vicinity of T_C , another sharp peak close to T_(OO) is clearly observed in the intensity of the spectra, which may be correlated with the structural transition and orbital ordering at this temperature. For the nanosized sample, a drastically different behavior is found. With a rhombohedral structure down to 70 K, the nanosized sample shows a ferromagnetic metallic ground state. The ESR studies reveal the coexistence of the paramagnetic and ferromagnetic resonance signals. The resonance intensity shows a broad peak around 200 K, which may be due to the wide ferromagnetic transition in the nanoparticle.