Collosal Magnetoresistance CMR in Manganites

The magnetoresistance of a solid is the change of resistance that occurs when a magnetic field is applied. The magnetoresistive (MR) ratio is defined as the change in resistance when a magnetic field is apphed to that in zero field  

The physical causes of intrinsic CMR are not yet clear. Originally believed to be associated with superexchange or double exchange, it is now thought that the important factor is the presence of ferromagnetic half-metallicity with majority spin 

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