Magnetotransport phenomena in A(Mn3-xCux)Mn4O12 (A = Ca, Tb, Tm) perovskites

The perovskites Ca(Mn3-xCux)Mn4O12 and ACu(3)Mn(4)O(12) (A =Tb, Tm) have be en synthesized using different processes and their magnetic and transport p roperties investigated. CaMn3Mn4O12 has been shown to be antiferromagnetic with T-N at approximately 85 K. This compound exhibits the resistivity drop more than one order of magnitude at 440 K due to the charge order-disorder transition. The substitution of manganese by copper leads to ferrimagnetic state developing through intermediate spin glass state. A clear increase o f both Te and magnetization value at low T is observed as the copper conten t increases up to x=1.5. For this particular x=1.5 composition, a metal-ins ulator transition is observed at 160 K, whereas for smaller Cu content a se miconducting behavior is exhibited. The Ca-free samples TbCu3Mn4O12 and TmC u3Mn4O12 are also ferrimagnets exhibiting a metal-like behavior below 360 K and a metal-insulator transition at 250 K for the former and the latter, r espectively. But the most interesting result deals with the magnetoresistan ce (MR) of all the ferrimagnetic samples that can reach up to 20% in I T at 77 K. The appearance of this MR is closely related to the antiferromagneti c Cu-Mn interactions development and, in contrast to colossal MR perovskite s, its value is no more maximum at Te but it increases continuously as T de creases. [S0163-1829(98)00246-X].