Emergence of spin–phonon coupling in a Gd-doped Y₂CoMnO₆ double perovskite oxide: a combined experimental and <i>ab initio</i> study

We present Raman spectroscopy results backed by first-principles calculations and investigate the nature of possible spin-phonon coupling (SPC) in a Gd-doped Y₂CoMnO₆ (YGCMO) double perovskite oxide. The influence of Gd substitution, A-site ordering and anti-site disorder is also studied. YGCMO exhibits anti-site disorder leading to both ferromagnetic (between Co and Mn) and antiferromagnetic interactions (Co-Co, Mn-Mn, and Gd-Co/Mn), making the SPC quite intriguing. Analysis of the temperature-dependent phonon frequencies for the stretching modes of YGCMO indicates that SPC here possibly emerges from the simultaneous presence of competing ferromagnetic and antiferromagnetic interactions. The SPC strength comes out to be 0.29 cm^-1. Our density functional theory (DFT) calculations show that phonon modes shifted towards lower frequency with Gd doping. Similarly, A-site ordering and anti-site disorder significantly alter the Raman spectra. Experimental findings are also corroborated by first-principles DFT calculations, which indicate that anti-site disorder and Gd doping enhance SPC in YGCMO. This implies the strong influence of A-site cationic radii and B-site (Co/Mn) ordering on SPC in the bulk double perovskite systems. The phonon dynamics of YGCMO are, therefore, correlated with magnetic ordering, indicating potential applications in spintronic devices.