Critical behavior of Nd0.67Ba0.33Mn1−xFexO3 (x=0 and 0.02) manganites

Abstract We used Banerjee’s criteria, modified Arrott plots and scaling hypothesis to analyze magnetic-field dependences of magnetization near the ferromagnetic–paramagnetic (FM–PM) phase-transition temperature ( T C ) of Nd 0.67 Ba 0.33 Mn 1− x Fe x O 3 ( x =0 and 0.02) manganites. Experimental results reveal that the two samples undergo a second-order phase transition and a critical exponents values ( β =0.326±0.005, γ =1.244±0.033, δ =4.740 at T C =145 K for x =0 and β =0.509±0.013, γ =1.140±0.117 and δ =3.011 at T C =134 K for x =0.02) slightly shifting from those of the 3D-Ising model and the mean field model, respectively. These exponents indicate that the exchange interaction J ( r ) ranges from r − 5 and r − 4.5 for x =0 (respectively J ( r ) r − 5 , for x =0.02). This is due to the fact that the substitution of Fe ions into the Mn site leads to the formation of a larger proportion of Mn 4+ with respect to Mn 3+ which reduces the ferromagnetic double-exchange interaction of Mn 3+ –Mn 4+ couples. By investigating the field dependence of the magnetic entropy change Δ S M , it was possible to evaluate the critical exponents of the magnetic phase transitions. Their values are in good agreement with those obtained from the critical exponents using a modified Arrott method.