Spin-glass shell and magnetotransport properties of a La_0.67Ca_0.33MnO₃ nanoring network

The magnetotransport and magnetic property of the La_0.67Ca_0.33MnO₃ (LCMO) nanoring network (NRN) have been investigated. This NRN-LCMO shows a giant magnetoconductance at low temperatures with strong memory effect of magnetic field. Its high field magnetoconductance shows linear field dependence with an anomalously abrupt increase of slope at about 4 T. The magnetic field dependence of the resistance peak in the resistance vs temperature curve strongly depends on the grain size. The most interesting results are the exchange bias effect of magnetization and the resistance relaxation at low temperatures, which suggest the existence of two types of spin glass in the shell of LCMO grains. The magnetotransport behavior of NRN-LCMO was explained by considering the role of the spin-glass shell in the tunneling process with a core-shell model. We emphasized that the shell layers are magnetized by both the external magnetic field and the internal magnetic field induced by the ferromagnetic cores. This work also indicates that the electronic transport of NRN-LCMO can provide some important information on the magnetic state of the nanograin shell.