Abstract :
The dc magnetization and ac susceptibility measurements on two dimensional layered manganite La1.2Ba1.8Mn2O7 samples reveal the occurrence of ferromagnetism above room temperature with ferromagnetic (FM) to paramagnetic (PM) transitions at 338 K. The bifurcation temperatures shown by the zero-field cooled (ZFC) and field cooled (FC) dc magnetization curves at high temperatures shift towards lower temperatures as the applied field is increased from 100 to 2500 Oe. The data are suggestive of a large magnetic anisotropy due to the strong competing ferromagnetic and antiferromagnetic interactions resulting in a spin-glass-like state. Ru doping is found to enhance the ferromagnetism and metallicity of the system in a remarkable way. The magnetoresistance (MR) values obtained are very high and about 40% even at 260 K for the undoped sample.
