The Magic of Manganites: Novel Fundamental and Practical Properties
La1-x(Ca,Sr,Ba)xMnO3 is prototypical example of manganese-oxide systems, where the electrons are highly correlated and display a wide variety of interesting physical properties due to the interplay of the charge, spin, lattice, and orbital degrees of freedom. The undoped (x=0) material is an antiferromagnetic insulator in its ground state, but for x~1/3 the material becomes a ferromagnetic metal. The transition with increasing temperature from ferromagnet to paramagnet is coincident with a metal insulator transition, which can be readily controlled with a magnetic field producing Colossal MagnetoResistance (CMR). We will explain the physics controlling this behavior (with a bit of history) and present our neutron and x-ray scattering results on this class of materials. One of the emerging features of these materials is their propensity to form intrinsically inhomogeneous structures on a variety of length scales, from full scale phase separation to nanoscale polarons in the CMR regime, the latter behavior being analogous to polar nanoregions in relaxor ferroelectrics, and spin and charge stripes in cuprates. The CMR work on manganites naturally evolved into the general realm of manganite multiferroics, which are insulators that exhibit both ferroelectricity and magnetic order. Typically these two disparate phenomena are mutually exclusive, making multiferroics rare, and rarer still are multiferroics where these two order parameters exhibit strong coupling. Recent work on multiferroics and related manganite systems will be presented, including "CMR" materials at higher doping (x>1/2) where charge/orbital ordering dominates and some become multiferroics. Potential uses for the above systems for magnetic recording, spintronics applications, and rechargeable batteries will be pointed out.
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