Effect of Cr substitution on structural, magnetic, magnetocaloric and critical behaviors of La0.7Y0.05Ba0.25MnO3 perovskite manganite

Abstract

A thorough investigation was conducted into the structural, magnetic, and critical properties of La 0.7 Y 0.05 Ba 0.25 Mn 1-x Cr x O 3 (x = 0 and 0.15) perovskite manganite synthesized using the sol-gel method. The samples possess an orthorhombic structure with the Pnma space group according to X-ray diffraction (XRD) patterns. The average ion radii of the B-site cation (< r B >), the unit cell volume ( V ), and <θ Mn,Cr – O – Mn,Cr > bond angle decreased with Cr substitution. While the average bond distance, < d Mn,Cr – O >, and Goldschmidt tolerance factor ( t G ) increased. The samples present a magnetic transition from a paramagnetic (PM) phase to a ferromagnetic (FM) phase at Curie temperature ( T C ). Addition of Cr to La 0.7 Y 0.05 Ba 0.25 MnO 3 decreased the T C value from 310 K (for x = 0 sample) to 258 K (for x = 0.15 sample). Using Banerjee's criteria, second-order phase transitions were determined for the samples. Both samples showed significant maximum entropy change | Δ S M max | and relative cooling power (RCP) whose values decreased from (6.40 J Kg −1 K −1 and 231 J Kg −1 for x = 0) to (4.45 J Kg −1 K −1 and 185 J Kg −1 for x = 0.15), respectively. These values indicate that the La 0.7 Y 0.05 Ba 0.25 Mn 1-x Cr x O 3 manganites exhibit favourable magnetocaloric effect (MCE) and demonstrate promising potential for application as materials in magnetic refrigeration technology. The estimated critical exponents ( β , γ , and δ ) for the x = 0 sample align with the 3D-Ising model, while for x = 0.15, they closely resemble the 3D-Heisenberg model. This shift in the universality class can be attributed to the interplay between competing ferromagnetic double-exchange and antiferromagnetic super-exchange interactions that exist within the prepared samples.

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