Evidence for Spin Glass Transition in Hexagonal $DyMnO_{3}$ without Substitutional Disorder

The magnetic interactions in the multiferroic hexagonal (h-) REMnO3 with magnetic RE3+ ions are geometrically frustrated, but only long-range ordering transitions have been reported so far. Using dc and ac susceptibility measurements on well-characterized single crystals of h-DyMnO3, we present here evidence for a spin glass (SG) transition around the spin-reordering transition at TDy3+ ≈ 7 K. This transition is shown to exhibit history-dependent irreversibility, de Almeida–Thouless line in the T–H plane, and critical slowing down of spin dynamics as per Vogel–Fulcher and power law. We have also confirmed that the SG phase exhibits nonexponential decay of thermoremanent magnetization, as well as memory and rejuvenation effects. The SG phase of h-DyMnO3 is unconventional as it occurs without any apparent disorder, like in other geometrically frustrated systems, but bears perfect phenomenological similarities with the SG phases in disordered systems. Using low-temperature X-ray diffraction studies, we also present experimental evidence for magnetoelastic coupling, which we believe is the source of randomness required for SG transition in the geometrically frustrated h-DyMnO3 in the absence of any substitutional disorder