We have studied structural, magnetic and electrical properties of bulk samples of Pr 1-x Ag x MnO 3 manganites and also LaFeO 3 , Ni/NiO and NiO nanoparticles. Firstly, we have investigated the role of Ag i Pr 1-x Ag x MnO 3 manganites. Detailed ac susceptibility measurements on the samples show unusual and interesting features, which are associated with the domain walls and the effects of grain-boundaries on their movements. We have proposed a mechanism based on the pinning of the magnetic domain walls at the grain-boundaries. The magnetocaloric effect, heat capacity, resistivity, magnetoresistance, FC/ZFC magnetization and hysteresis loops at different temperatures have been also studied. We report the first observation of exchange-bias effect in LaFeO 3 nanoparticles. After field cooling from room temperature, the exchange bias increases while the coercivity decreases with decreasing temperature. Thermally activated reversal of the AFM spins can explain the appearance of exchange bias without the conventional field cooling the sample through the Néel temperature, as well as the temperature dependence of exchange bias and coercivity. The Ni/NiO nanoparticles have been prepared using a relatively new method and their magnetic properties have been studied. The advantage of this method is that the percentage of Ni can be easily controlled by the heating temperature. Finally, a rapid and simple method has been used to prepare NiO nanoparticles, which is also suitable to prepare other metal oxides.