Griffiths-like phase, spin-phonon coupling, and exchange-bias in the disordered double perovskite GdSrCoMnO${}_6$

Abstract

We report structural, magnetic, and Raman studies of the disordered double perovskite GdSrCoMnO${}_6$~(GSCM). DC magnetization shows a ferromagnetic transition at $T_C\approx 153$~K. The inverse susceptibility exhibits a downturn above $T_C$ and is consistent with a Griffiths-like regime extending up to $T_G\approx 172$~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 $T_f\approx 30$~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 $|H_{EB}|=379$~Oe at 5~K. Structural disorder therefore plays an important role in the magnetic correlations, spin dynamics, and spin-lattice response of GSCM.

13 pages, 10 figures