Temperature and magnetic field dependence of conduction noise in double layered La1.4Ca1.6Mn2O7 manganite

Bulk samples of double layered manganite La1.4Ca1.6Mn2O7 were prepared by solid-state reaction method. Study of magnetotransport properties revealed a metal to insulator transition at 160 K, a ferromagnetic transition at 164 K and appearance of two-dimensional short range ferromagnetic correlations around 235 K. The temperature dependence of conduction noise showed three peaks at 114 K, 165 K and 235 K which are attributed to excess noise generated due to setting up of three-dimensional out-of-plane ferromagnetic transition, two-dimensional out-of-plane ferromagnetic transition temperatures and appearance of two-dimensional short range ferromagnetic correlations respectively. In the temperature region - 160 K, excess noise was also generated due to the metal-insulator transition. In the paramagnetic region, conduction noise was found to remain unchanged with the applied magnetic field whereas in the ferromagnetic regions, the peaks at 114 K and 235 K got disappeared. The latter is attributed to the suppression of spin fluctuations.