Griffiths-like phase, spin-phonon coupling, and exchange-bias in the disordered double perovskite GdSrCoMnO₆

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We report structural, magnetic, and Raman studies of the disordered double perovskite GdSrCoMnO₆ (GSCM). DC magnetization shows a ferromagnetic transition at TC ≈ 153 K. The inverse susceptibility exhibits a downturn above TC and is consistent with a Griffiths-like regime extending up to TG ≈ 172 K. Raman measurements show a deviation of the phonon frequency from the anharmonic background near the magnetic-ordering region, consistent with spin-phonon coupling. AC susceptibility indicates slow magnetic dynamics below the freezing temperature Tf ≈ 30 K. These results point to magnetic inhomogeneity generated by the random distribution of mixed-valence Co and Mn ions and by the resulting competition between ferromagnetic and antiferromagnetic interactions. In the low-temperature regime, an exchange-bias effect is observed up to 50 K, with an exchange-bias magnitude |HEB| = 379 Oe at 5 K. Structural disorder therefore plays an important role in the magnetic correlations, spin dynamics, and spin-lattice response of GSCM.