Studi struktur, sifat listrik dan magnet material perovskite manganite La0, 7Sr0, 2ba0, 1Mn1-xNixO3 (x = 0; 0,02; 0,05; 0,1) = Study of structure, electrical and magnetic properties of perovskite manganite materials La0, 7Sr0, 2ba0, 1Mn1-xNixO3 (x = 0; 0.02; 0,05; 0,1)