Low-field magnetic properties of La1−Ca MnO3 (0⩽x⩽0.4)
摘要
Magnetic properties of cubic La1−xCaxMnO3 (0⩽x⩽0.4) are investigated between T=5 and 310 K in the external field of 2 G. The dependence of the ferromagnetic transition temperature on x is analyzed with the model of spin polarons associated with electronic localization and electron–electron interaction. The bandwidth of the localized electrons is found to be W=1.90±0.05 eV. In the samples with x<0.2 and the Mn4+ concentration c<0.26, a transition to a canted antiferromagnetic spin state is observed. The dependence of the transition temperature, T1, 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⩽0.2 and c⩽0.22 the value of the critical exponent, γ=1.21±0.05, is obtained for the temperature dependence of the zero-field-cooled susceptibility function χ−1 (T)∼(T−TC)γ, for T>TC.