Magnetocaloric and critical behavior studies in (Nd1-xYx)2CoMnO6 (x = 0.0 to 0.6) double perovskites

Abstract

This study explores the double perovskite compounds (Nd_1-xY_x)₂CoMnO₆ (x = 0.0–0.6), with a focus on their structural, and magnetic properties. The magnetocaloric effect and critical behavior are highlighted in the magnetic studies. The samples are synthesized using the gel combustion method and confirmed to crystallize in a monoclinic structure (P2₁/n space group). With increasing Y concentration, a reduction is observed in the lattice parameters, unit cell volume, crystallite size, and grain size. The paramagnetic (PM) to ferromagnetic (FM) transition temperature (T_C) is observed to be 176 K in the parent sample and 122 K in the x  = 0.6 sample. The long- range FM ordering is primarily driven by the super-exchange interaction between Co²⁺ and Mn⁴⁺ ions, mediated through oxygen. Raman studies performed at low temperatures (around T_C) provide insights into the spin-phonon coupling. Magnetization curves with a maximum field of 9 kOe were measured for x  = 0.0 and 0.4 samples around their respective T_C values to investigate the magnetocaloric effect. Arrott plots indicate that both samples exhibit second-order PM-FM phase transitions near T_C. For the parent sample, the maximum magnetic entropy change (−Δ $S_M^{\max }$) and the relative cooling power (RCP) were determined to be 4.75J/kgK and 177.2 J/kg, respectively at 9 T. Moreover, the critical behavior was analyzed using modified Arrott plots, and the critical exponents (β, γ, δ) were calculated. The validity of these determined critical exponents was confirmed through scaling hypothesis.