La_(0.7)Ca_(0.3-x)Sr_xMnO_3 Manganites: Effect of Structure on the Magnetic and Transport Properties

摘要

The effect of lattice structure on the magnetic and transport properties of La_(0.7)Ca_(0.3-x)Sr_xMnO_3 (x = 0; 0.03; 0.06; …; 0.3) lanthanum manganites have been studied. Curie temperature pressure coefficient, dT_c/dP, showed the dependence on x value. Temperature T_c increased almost linearly under applied pressure as dT_c/dP ≈ 7.5 K/GPa in the orthorhombic (Pbnm) and rhombohedral (R3c) phases, respectively. The value of dT_c/dP (≈3.5 K/GPa) showed a minimum and a temperature of the resistance maximum, T_p(x), showed a change of slope at x = 0.15, corresponding to the concentration structural phase transition. Differences between the values of dT_c/dP and slopes of T_p versus x in Pbnm and R(3-bar)c phases are explained by the different effect of external pressure on the Mn-O bond length and Mn-O-Mn bond angle, and by the different internal pressure effect in those phases, respectively.