Low-field magnetic properties of La1-xCaxMnO3 (0 <= x <= 0.4)

Magnetic properties of cubic La1-xCaxMnO3 (0 less than or equal to x 0.4) a re investigated between T = 5 and 310 K in the external field of 2 G. The d ependence of the ferromagnetic transition temperature on,x is analyzed with the model of spin polarons associated with electronic localization and ele ctron-electron interaction. The bandwidth of the localized electrons is fou nd to be W = 1.90 +/- 0.05 eV. In the samples with x < 0.2 and the Mn4+ con centration c < 0.26, a transition to a canted antiferromagnetic spin state is observed. The dependence of the transition temperature, T,, on c can be well described by a model including the Mn3+-Mn3+ superexchange and the Mn3 +-Mn4+ double-exchange interactions. In the samples with,x less than or equ al to 0.2 and c less than or equal to 0.22 the value of the critical expone nt, y = 1.21 +/- 0.05, is obtained for the temperature dependence of the ze ro-field-cooled susceptibility function chi(-1) (T) similar to (T - T-C)(y) , for T > T-C. (C) 2000 Elsevier Science B.V. All rights reserved.