Abstract
Byline: M. Khlifi (a), A. Tozri (a), M. Bejar (a), E. Dhahri (a), E.K. Hlil (b) Keywords: Manganite; Critical behavior; Critical exponent; Phase transition The critical behavior associated with the magnetic phase transition has been investigated by magnetization isotherms in La.sub.0.8Ca.sub.0.2MnO.sub.3 and La.sub.0.8Ca.sub.0.1a .sub.0.1MnO.sub.3 (a is the calcium deficiency). The critical exponents are estimated by various techniques such as the Modified Arrott plot, Kouvel-Fisher plot and critical isotherm technique. The critical exponents values for La.sub.0.8Ca.sub.0.2MnO.sub.3 are very close to those found out by the 3D-Ising model ([beta]=0.328, [gamma]=1.180, and [delta]=4.826 at an average T.sub.C =181.676K). Moreover, the estimated critical exponents of La.sub.0.8Ca.sub.0.1a .sub.0.1MnO.sub.3 are consistent with the prediction of the 3D-Heisenberg model ([beta]=0.357, [gamma]=1.167, and [delta]=4.802 at an average T.sub.C =178.182K). We noted that the critical exponents [gamma] are almost similar to the value of the mean-field theory which can be explained by the existence of a long-range dipole-dipole interaction. Following the Harris criterion, we deduced that the disorder in our case is relevant, which can be the cause of the change in the universality class. Author Affiliation: (a) Laboratoire de Physique Appliquee, Faculte des Sciences de Sfax, Universite de Sfax, BP 1171, Sfax 3000, Tunisie (b) Institut Neel, CNRS -- Universite J. Fourier, BP 166, 38042 Grenoble, France Article History: Received 27 January 2012; Revised 12 February 2012