Landau theory and critical behavior near the ferromagnetic-paramagnetic transition temperature in Pr0.63A0.07Sr0.3MnO3 (A=Pr, Sm and Bi) manganites

In this work, we are interested in the study of the critical behavior and the Landau theory of Pr0.63A0.07Sr0.3MnO3 (A=Pr, Sm and Bi) compounds. The critical exponents of all our samples were studied using the magnetic field dependent isothermal magnetization around Curie temperature TC, based on various techniques. The validity of our critical exponents is confirmed by the scaling analysis. The study revealed that tricritical mean field model is the best for calculating the critical exponents for all our samples. The substitution of praseodymium by samarium and bismuth does not change the universality class. Using Landau theory, we have confirmed that the magnetic transition around TC is of second-order. An agreement was found between the (-ΔS) values estimated by Landau theory and those obtained using Maxwell relation for a magnetic field equal to 2 T, which shows the validity of this theory for all our compounds. The deviation obtained for bismuth and samarium based samples below TC can be attributed to the existence of some antiferromagnetic domains in the ferromagnetic phase.