Comparison of the order of magnetic phase transitions in several magnetocaloric materials using the rescaled universal curve, Banerjee and mean field theory criteria

Abstract

Magnetocaloric materials with second order phase transition near the Curie temperature can be described by critical phenomena theory. In this theory, scaling, universality, and renormalization are key concepts from which several phase transition order criteria are derived. In this work, the rescaled universal curve, Banerjee and mean field theory criteria were used to make a comparison for several magnetocaloric materials including pure Gd, SmCo1.8Fe0.2, MnFeP0.46As0.54, and La0.7Ca0.15Sr0.15MnO3. Pure Gd, SmCo1.8Fe0.2, and La0.7Ca0.15Sr0.15MnO3 present a collapse of the rescaled magnetic entropy change curves into a universal curve, which indicates a second order phase transition; applying Banerjee criterion to H/σ vs σ2 Arrot plots and the mean field theory relation |ΔSM| ∝ (μ0H/Tc)2/3 for the same materials also determines a second order phase transition. However, in the MnFeP0.46As0.54 sample, the Banerjee criterion applied to the H/σ vs σ2 Arrot plot indicates a first order magnetic phase transition, while the mean field theory prediction for a second order phase transition, |ΔSM| ∝ (μ0H/Tc)2/3, describes a second order behavior. Also, a mixture of first and second order behavior was indicated by the rescaled universal curve criterion. The diverse results obtained for each criterion in MnFeP0.46As0.54 are apparently related to the magnetoelastic effect and to the simultaneous presence of weak and strong magnetism in Fe (3f) and Mn (3g) alternate atomic layers, respectively. The simultaneous application of the universal curve, the Banerjee and the mean field theory criteria has allowed a better understanding about the nature of the order of the phase transitions in different magnetocaloric materials.

The magnetocaloric effect with critical behavior of a periodic Anderson-like organic polymer

“…6(b) presents a nearly parallel linear relation of the ln(ÀDS)-ln(h) curve at T C with n = 0.648 for different V values, which is basically consistent with the experimental observation of perovskite manganites Pr 0.55 Sr 0.45 MnO 3 and Nd 0.55 Sr 0.45 MnO 3 corresponding to the conventional ferromagnets taking the mean field value 2/3. 22,23,36,37 The linear fits in Fig. 6(c) demonstrate the validity of the relationship ÀDS p h 0.648 at around T C that characterizes a second order phase transition, which is close to ÀDS p h 2/3 for conventional ferromagnets obeying the mean field theory.…”

“…6(c) demonstrate the validity of the relationship ÀDS p h 0.648 at around T C that characterizes a second order phase transition, which is close to ÀDS p h 2/3 for conventional ferromagnets obeying the mean field theory. 36,37 Of particular interest is the scaling law related to the critical exponent b, g, and d, which obey the following relation at T = T C : 19,20,22,23 n(T C ) = 1 + (b À 1)/(b + g) = 1 + 1/d(1 À 1/b). (13) Herein, the critical exponents (b, g, and d) are determined by a detailed scaling analysis based on the Arrott-Noakes equation of state, 38 which are defined for the spontaneous magnetization M s (T), inverse initial susceptibility w 0 À1 , and critical isotherm (M(h)) at T C with the reduced temperature t = (T À T C )/T C as follows: 20,24,[38][39][40][41]…”

Tuning Magnetic Entropy Change and Relative Cooling Power in La0.7Ca0.23Sr0.07MnO3 Electrospun Nanofibers

“…Based in Banerjee criterion, a positive or negative slope in ⁄ vs. curves determine the order of the magnetic phase transition. A positive slope indicates a second-order magnetic phase transition, whereas a negative slope indicates a first order magnetic phase transition [21]. From the data obtained, a positive slope is noticed for La0.7Ca0.23Sr0.07MnO3 nanofibers with heat treatments at 973 K, 1073 K and 1173 K, which is a proof of second-order magnetic phase transition.…”

Second-order magnetic critical points at finite magnetic fields: Revisiting Arrott plots

“…Since then, the Banerjee criterion has been widely used whenever indications of temperature-induced first-order transitions were observed, in particular for metamagnetic isothermal magnetic-field measurements [17][18][19][20][21]. As a drawback of the Banerjee criterion, it can be noticed that while the (negative) slope is expected to increase continuously with increasing temperature, as originally pointed out in Banerjee's work [15], this is not observed in most of the experimental examples which use the criterion to propose first-order transitions [21][22][23][24].…”