Two types of chemical-pressure effects on the Verwey-type transition in BaSmFe2O5 are studied, viz., ionic-size contractions at the Ba and Sm sites. Whereas the replacement of Sm by the smaller Eu and Gd atoms increases the transition temperature TV from 232 K to 264 K, the Sr-for-Ba substitution decreases it from 232 K to 180 K for x=0.15 in (Ba1-xSrx)SmFe2O5. Of various structural parameters determined by synchrotron x-ray diffraction above T V, the magnitude of the orthorhombic distortion (=b-a) is found to correlate with TV in a manner that unifies both substitution schemes. It is suggested that when an increase in b-a above TV is achieved by means of the structural substitution, it makes it easier for the dxz Fe2+ orbital ordering to occur below TV.
|Journal||Physical Review B - Condensed Matter and Materials Physics|
|Publication status||Published - 1 Oct 2004|
|MoE publication type||A1 Journal article-refereed|