Magnetoelastic properties of Jahn-Teller crystals with colossal magnetoresistance

摘要

The cooperative Jahn-Teller effect in the low doped La{sub}(1-x)Sr(Ba){sub}xMnO{sub}3 crystals with colossal magnetoresistance is considered. Experimentally observed magnetoelastic properties like metamagnetoelasticity and magnetic field induced structural phase transitions are explained on the basis of the developed microscopic approach. It is proposed that the presence of an excited electronic orbital triplet, located relatively close to the ground Mn{sup}(3+)-electronic state, is fundamentally important for the understanding the experimental magnetic and magnetoelastic data. The existence of the excited triplet state separated by a small energy gap from the ground doublet is in agreement with the Tanabe -Sugano theoretical energy diagrams and is supported by the infrared absorption and Raman scattering measurements. Numerous calculations of the temperature and external magnetic field dependence of different crystal characteristics are made. Those calculations are in qualitative agreement with the experimental results.