ALAMN(2)O(6-Y) (A=K, RB) - NOVEL FERROMAGNETIC MANGANITES EXHIBITING NEGATIVE GIANT MAGNETORESISTANCE

We report the synthesis of a new series of manganese oxides, ALaMn(2)O (6-y), for A = K, nb, and Cs, that adopt an ordered superstructure of the perovskite. The Ii and Rb phases are tetragonal (a(t) similar to 7 .75, c(t) similar to 7.10 Angstrom) and the Cs phase is orthorhombic ( a(0) = 5.511, b(0) = 5.468, c = 7.311 Angstrom) indicating 2a(p) x 2a( p) and root 2a(p) x root 2a(p) x 2a(p) (a(p) = perovskite subcell) sup erstructures, respectively. The K and Rb phases are ferromagnetic (T-c similar to 327 and 300 K) metals, exhibiting a giant magnetoresistanc e behavior similar to alkaline earth metal substituted lanthanide mang anites. The results reveal that it is possible to induce Mn(III)I Mn(T V) mixed valency and the related electronic properties through action deficiency in ordered perovskites of the kind ALaMn(2)O(6).