Progressive substitution of La by Bi in the mixed oxides (LaBi)(0.7)Ca0.3MnO3 leads to great changes in the magnetic and transport properties of these compounds. From neutron diffraction experiments performed at D1B and D2B apparatus in the ILL, we have observed changes in the magnetic structure from ferromagnetic La0.65Bi0.05Ca0.3MnO3 to antiferro Bi0.7Ca0.3MnO3. The intermediate compounds show antiferromagnetism in a crystalline plane and ferromagnetism in the perpendicular direction. The distance Bi-O turns out to be shorter than the La-O due to the covalent character of the former. This can explain the increasing localization of the 3d electrons of Mn atoms and the insulating character of Bi0.7Ca0.3MnO3.
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