Raveau B
Laboratoire CRISMAT, UMR 6508, CNRS ENSICAEN, 6 Boulevard Maréchal Juin, 14050 Caen, Cedex 4, France.
Philos Trans A Math Phys Eng Sci. 2008 Jan 13;366(1862):83-92. doi: 10.1098/rsta.2007.2141.
The mixed valence Mn3+/Mn4+ and Co3+/Co4+ in manganites and cobaltites with the perovskite structure is absolutely necessary for the appearance of magnetotransport properties. It is shown that in these systems the Jahn Teller effect of the transition element, the charge and orbital ordering and the oxygen stoichiometry play a key role in the appearance of large and even colossal magnetoresistance. It has been discovered that these oxides exhibit a new phenomenon, the crystallographic and electronic phase separation. It is this phenomenon that is at the origin of the competition between ferromagnetism and antiferromagnetism or spin glass behaviour and which leads to the negative magnetoresistance (MR). The doping of these materials at different sites appears then to be a means of inducing large MR effects.
具有钙钛矿结构的锰酸盐和钴酸盐中的混合价态Mn3+/Mn4+和Co3+/Co4+对于磁输运性质的出现是绝对必要的。结果表明，在这些体系中，过渡元素的 Jahn-Teller 效应、电荷和轨道有序化以及氧化学计量比在大的甚至巨磁电阻的出现中起关键作用。已经发现这些氧化物表现出一种新现象，即晶体学和电子相分离。正是这种现象导致了铁磁性与反铁磁性或自旋玻璃行为之间的竞争，并导致了负磁电阻（MR）。那么在不同位置对这些材料进行掺杂似乎是诱导大的磁电阻效应的一种手段。
