Colossal magnetoresistance CMR

The identification and study of colossal magnetoresistance (CMR) materials could be amenable to combinatorial-style searches. Such approaches could be useful for elucidating the structural and electronic phase diagrams of these fascinating materials. Ultimately this could help sort out the apparently complex physics that underlies their behavior. An indication of the value of these approaches was recently provided by Xiang et al. [21]... 

In this article, we discuss spin, charge and orbital orders in transition metal oxides, in particular, in the rare-earth manganites which have become famous since 1993 owing to the phenomenon of colossal magnetoresistance (CMR) exhibited by them (Rao Raveau 1998). We also touch upon the issue of electronic inhomogeneities we discuss the signatures of the presence of such inhomogeneities and theoretical approaches to understand the same. 

Colossal magnetoresistance (CMR) is observed below 300 K in manganese perovskite structures [7] this has not been used in technology. 

The electrical transport properties of rare earth manganites with perovskite-type structure have been extensively studied in recent years because of the colossal magnetoresistance (CMR) effect or potential applications as catalysts. In most cases the general formula of rare earth manganites used in these studies are Ln,, (A,(Mn03, where A is a divalent ion (A = Ba, Sr, Ca, Pb) substituting for La. 

Excluding the cuprate superconductors, manganese per-ovskite oxides that exhibit the so-called colossal magnetoresistance (CMR) effect constitute, probably, the most extensively studied set of materials over the past decade or so. Several review articles exist. ... 

Another area that has been of interest since the development of this field is that of metal oxides. Simple metal oxides such as MgO provide a test bed for new methods. More complex oxides have attracted much interest for their commercially important properties—solid electrolytes, ferroelectrics, catalysts, semiconductors, superconductors, multiferroics. Relatively simple calculations can, for example, track the path of ions through ionic conductors and suggest alternative solids for fuel cells or batteries. Solids with interesting electrical and magnetic properties such as high Tc superconductors and solids showing colossal magnetoresistance (CMR) have been... 

Perovskites have also received much attention since 1986 because the superconducting oxide YBCO contains perovskite structural elements. The importance of this structure was again realized in 1993 when the phenomenon of colossal magnetoresistance (CMR) was discovered in a range of manganate ceramics with a layered perovskite structure similar to that found in YBCO and other high-temperature superconductors. 

In this chapter the focus is upon electronic conductivity in perovskites. The electrons in perovskites are believed to be strongly correlated that is, they do not behave as a classical electron gas, but are the subject to electron-electron interactions. This leads to considerable modification of the collective electron behaviour of the conduction electrons, resulting in metal-insulator transitions, high-temperature superconductivity, half-metals and colossal magnetoresistance (CMR). The effects of strong correlation are important for the 3d, 4d and4f elements. In many ways the topics described here are thus a continuation of the previous chapter on magnetic perovskites, and in truth the two subject areas cannot be separated in a hard and fast maimer. 

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