On the ferromagnetic perovskite with potential GMR properties: The manganite La1-xKxMnO3

We investigate structural features (cell distortions), magnetic and electri c properties versus temperature for La1-xKxMnO3 (0.05 < x < 0.2) perovskite s. All the phases crystallize in a rhomboedral symmetry (R (3) over bar c) and are ferromagnetic. Curie temperatures are strongly dependent of x, with a maximum around 308 K for La0.8K0.2MnO3. A sharp decrease of the resistiv ity is observed just below the Curie temperature, accompanied by a very ste ep increase of the spontaneous magnetization, characteristic of a conventio nal Brillouin type curve. The average magnetic moment of Mn is about 88 e.m .u/g at 5 K for the composition La0.8K0.2MnO3. The transition from ferromag netic-metallic to paramagnetic-semiconducting states is explained from the suggested distribution of the cations (La1-x3+Kx+)(A)(Mn1-2x4+Mn2x4+)BO3 by the double exchange of Mn3+-Mn4+ pairs at the B-sublattice. Preliminary ma gnetoresistance measurements on bulk ceramic samples display an MR effect o f the same amplitude as in the case of the alkaline earth substituted La ma nganites.