Identification of a Griffiths singularity in a geometrically frustrated antiferromagnet

We report the observation of a Griffiths Phase in the geometrically frustrated antiferromagnet DyBaCo${}_4$O${}_{7+\delta }$. Its onset is determined using measurements of the thermoremanent magnetization, which is shown to be superior to conventional in-field measurement protocols for the identification of the Griffiths Phase. Within this phase, the temporal relaxation of magnetization exhibits a functional form which is expected for Heisenberg systems, reflecting the nature of spin interactions in this class of materials. Interestingly, the effective Co${}^{2+}$/Co${}^{3+}$ ratio tailored by varying the oxygen non-stoichiometry $\delta$ is only seen to influence the antiferromagnetic ordering temperature ($T{}_N$), leaving the Griffiths Temperature ($T{}_G$) invariant.