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The goal of this thesis is to understand the physical properties of lanthanum based manganites and barium based ruthenates. In order to obtain negative colossal magnetoresistance in manganites and fabrication of barium ruthenate in ordinary condition, the effects of variables such as ionic radii, chemical composition, temperature, magnetic field and processing in manganites and ruthenates systems are investigated. In the first part, the effects of potassium doping on structure, metalinsulator transition and magnetoresistance in )La1-yKy)0.7 Ca0.3 MnO3 and)La1-yKy)0.7 Ba0.3 MnO3 manganites systems are studied. Polycrystalline samples of manganites are synthesized by the sol‐gel method. In the... 

In this thesis, we have studied systems called Ruthenates, which are common in possessing Ru element in their chemical compounds. Ruthenates are a group of transition metal oxides which have attracted so attention, especially in last years duo to their rich phase diagram which shows different orbital, charge and spin orderings.They cover a vast range of materials properties, from a Superconductor to Mott Hubbard insulator, from a paramagnetic metal to an antiferromanetic insulator. In these systems, substituting a covalent atom with structure base, leads to a vast variety changing, not only in electronic properties but also in magnetic and structural ones: Although Sr"RuO£ is a...