First-order-like ferromagnetic transition in (La1-yPry)1-x(Ca1-zSrz)xMnO3 (x ∼ 0.25)

The magnetization M(T), electrical resistivity rho(T) and thermal conductivity kappa(T) have been measured for the manganese oxides, R(0.75)A(0.25)MnO(3) (R = La1-yPry: A = Ca1-zSrz) (0 less than or equal to y less than or equal to 1.0, 0 less than or equal to z less than or equal to 1.0). Two types of the first-order-like ferromagnetic transition have been verified; the transition shows no hysteresis for 1.345 less than or equal to r(RA) less than or equal to 1.362 Angstrom (r(RA) = average ionic radius of R-A site), while it accompanies hysteresis for 1.320 < r(RA) < 1.345 Angstrom. For r(RA) > 1.362 Angstrom and r(RA) < 1.320 Angstrom, the ferromagnetic transition is of the second order. The order of the transition may be closely correlated with the strength of the electron-phonon coupling as Millis et al. have predicted. (C) 2000 Elsevier Science B.V. All rights reserved.