Relation between giant volume magnetostriction, colossal magnetoresistance, and crystal lattice softening in manganites La1−x AyMnO3 (A = Ca, Ag, Ba, Sr)

Abstract

Giant volume magnetostriction (GVM) is detected near the Curie temperature T{sub C} in La{sub 1-x}A{sub x}MnO{sub 3} single crystals (A = Ca, Sr, Ba, 0.1 {<=} x {<=} 0.3) and above T{sub C} in La{sub 1-x}Ag{sub y}MnO{sub 3} (x = y = 0.15, 0.2 and x = 0.2, y = 0.1) ceramics (in the latter system, giant volume magnetostriction attains a value of 6.5 x 10{sup -4} in a magnetic field of 8.2 kOe). The behavior of GVM and colossal magnetoresistance (CMR) is found to be the same: both quantities have negative values, the temperature dependences of their absolute values pass through a peak, and the isotherms do not exhibit saturation up to the maximal measuring fields of 130 kOe. In compounds with compositions La{sub 0.7}Ba{sub 0.3}MnO{sub 3} and La{sub 0.85}Ag{sub 0.15}MnO{sub 3}, GVM and CMR were observed at room temperatures (in a magnetic field of 8.2 kOe, GVM attains values of 2.54 x 10{sup -4} and 2 x 10{sup -4} and CMR is equal to 11.6 and 11.2%, respectively). Both phenomena are attributed to the presence of a magnetic (ferromagnetic-antiferromagnetic) two-phase state in these systems, which is associated with a strong s-d exchange. It is found that the maximummore » value of the GVM in single crystals of La{sub 1-x}A{sub x}MnO{sub 3} (A = Ba, Sr, Ca, Ag) depends on the radius R{sub A} of cation A (it is the higher, the larger the difference |R{sub A}-R{sub LA{sup 3}{sup +}}|). The only exception is the compound with A = Ag, in which the pattern is complicated by additional defectiveness. Local disorder in the La{sub 1-x}A{sub x} sublattice, which is associated with the presence of cations with different radii, leads to a displacement of oxygen ions and to crystal lattice softening. The exchange s-d interactions in La{sub 1-x}A{sub x}MnO{sub 3} (A = Ca, Sr, Ba, Ag) are found to be comparable with electrostatic interactions ensuring the existence of the crystal; this facilitates manifestation of the GVM.« less