Crystal symmetry and pressure effects on the properties of mixed-valence manganites

A lattice structure effect on the magnetic and magnetotransport properties of La0.7Ca0.3-xSrxMnO3 lanthanum manganites have been studied. The Curie temperature-pressure coefficient increased almost linearly under an applied pressure as dT(c)/dP approximate to 14 K/GPa and as dT(c)/dP approximate to 7.5 K/GPa in the orthorhombic and rhombohedral structures, respectively. This is caused by the different pressure effect on the Mn-O bond distances and on the Mn-O-Mn bond angles in those phases. The anomalous low value of dT(c)/dP(approximate to 3.5 K/GPa) for La0.7Ca0.15Sr0.15MnO3 composition and a jump of the magnetoresistance maximum value at the concentrational Pbnm <----> R (3) over barc phase transition were observed and discussed. (C) 2002 Elsevier Science B.V. All rights reserved.