Abstract
The critical behaviour of Pr0.5Sr0.5−xAgxMnO3 (0 ≤ x ≤ 0.2) samples around the paramagnetic–ferromagnetic phase transition is studied based on isothermal magnetization measurements. The assessments based on Banerjee's criteria reveal the samples undergoing a second-order magnetic phase transition. Various techniques such as modified Arrott plot, Kouvel–Fisher method, and critical isotherm analysis were used to determine the values of the ferromagnetic transition temperature TC, as well as the critical exponents of β, γ and δ. The values of critical exponents, derived from the magnetization data using the Kouvel–Fisher method, are found to be (β = 0.43 ± 0.002, 0.363 ± 0.068 and 0.328 ± 0.012), (γ = 1.296 ± 0.007, 1.33 ± 0.0054 and 1.236 ± 0.012) for x = 0.0, 0.1 and 0.2, respectively. This implies that the Pr0.5Sr0.5−xAgxMnO3 with 0 ≤ x ≤ 0.2 systems does not belong to a single universality class and indicates that the presence of magnetic disorder in the system must be taken into account to fully describe the microscopic interaction of these manganites. With these values, magnetic-field dependences of magnetization at temperatures around TC can be well described following a single equation of state for our samples. From magnetic entropy change (ΔSM), 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 plot (MAP). We used the scaling hypotheses to scale the magnetic entropy change and heat capacity changes to a universal curve respectively for Pr0.5Sr0.5−xAgxMnO3 samples.
Highlights
IntroductionThe study of phase transitions in manganites is of special importance, since the relationship between the ferromagnetism, colossal magnetoresistance (CMR) and magnetocaloric effect (MCE) have been a topic of great interest due to the complexity of their magnetic phase diagram
Since the discovery of colossal magnetoresistance (CMR) in perovskite-manganites, extensive efforts have been carried out theoretically and experimentally to investigate the physical properties of these materials.[1,2,3]. These oxide systems showing multifunctional properties have always had a fascination with science and technology and this has developed into research interests due to the rich fundamental physics and their presence in useful applications including magnetocaloric effect (MCE).[4,5,6]
The study of phase transitions in manganites is of special importance, since the relationship between the ferromagnetism, CMR and MCE have been a topic of great interest due to the complexity of their magnetic phase diagram
Summary
The study of phase transitions in manganites is of special importance, since the relationship between the ferromagnetism, CMR and MCE have been a topic of great interest due to the complexity of their magnetic phase diagram. Ferromagnetic Pr-based manganites are intrinsically inhomogeneous, both above and below FM–PM transition temperature (TC) due to coexistence of FM and antiferromagnetic (AFM) interactions.[14] to get more information about FM–PM transition nature, it is important to study in detail the critical exponents associated with the transition.[15] This analysis can provide us the order, the universality class, and the effective dimensionality of the phase transition around the Curie temperature TC.[16] This practice of assigning such universal classes based on theoretical spin–spin interaction models (like mean eld, 3D- Ising or 3D- Heisenberg) has been useful in trying to discern the intricacies of magnetic transitions in real systems.[17] Several experimental studies of critical phenomena were previously made on ferromagnetic manganites.[18,19,20,21] the critical behaviour of manganites near the PM–FM phase transition by using a variety of techniques have yielded a wide range of values for the critical exponent b. Scaling analysis was used in order to check the validity of these exponents
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