Short-Range Magnetic Correlations and Thermally Assisted Spin Tunnelling in Distorted Diamond Lattices RTaO₄ (<i>R</i> = Tb and Dy)

Rare earth-based frustrated systems provide an excellent platform to study novel magnetic phenomena owing to their localized moment and unquenched orbital momentum. Here, we present a comprehensive investigation of crystallographic and thermodynamic properties of TbTaO₄ and DyTaO₄, wherein the magnetic ions form a distorted diamond structure. The former exhibits a crossover from short-ranged magnetic correlations to long-ranged antiferromagnetic ordering at ∼2.2 K, while the latter manifests only short-ranged magnetic correlations down to 1.8 K. Interestingly, a field-induced frequency dependence is observed in AC susceptibility in both cases, similar to that observed in spin ice systems. Analysis using the Casimir-duPre plot and Arrhenius law confirms that the origin behind this spin relaxation is thermal in nature, with activation energy close to the first excited crystal electric field gap. Our studies suggest that the observed frequency-dependent behavior is not only limited to spin ice materials, but it is a generic phenomenon in a broader class of rare earth-based frustrated magnetic systems.