Invar effect accompanying charge order in La0.25Ca0.75MnO3

Abstract

To determine the role of the Jahn-Teller effect in the orbital and charge ordering of mixed crystals of the strongly correlated La1-xCaxMnO3 system, we have used the diffraction of synchrotron radiation and the subsequent Rietveld analysis of diffraction patterns in order to obtain structural data for La0.25Ca0.75MnO3 compound in the temperature range from 90 to 325 K with a step of ∼2 K. For the first time for this compound, an Invar effect was observed below the charge-order temperature. In the entire temperature range, atomic displacements were analyzed and correlations between charge ordering and deformational modes were made, on the basis of which the secondary role of the Jahn-Teller effect in observed structure distortions was established. A hypothesis of a spin crossover in the vicinity of the charge-ordering temperature is proposed that describes adequately both the obtained structural data and the results of measurements of the macroscopic magnetic and elastic properties of the studied compound as well as related materials with charge ordering.