Evolution of Griffiths-like Anomaly in Isostructural Swedenborgite Compounds Ho1−xErxBaCo4O7+δ

In this study, we investigate the presence of the Griffiths-like anomaly in the geometrically frustrated antiferromagnet HoBaCo4O7+δ and globally its absence in ErBaCo4O7+δ, despite only small differences in the ionic radii, f-electron occupancy, and the corresponding crystal structures of the Ho3+ and Er3+-members. Previous studies have identified the Griffiths phase in the Dy-analog, DyBaCo4O7+δ, suggesting certain inherent features of this class of materials that regularly give rise to such anomalies. To explore the curious disappearance of such an anomalous feature in ErBaCo4O7+δ, we prepared a series of compounds with varying compositions Ho1−xErxBaCo4O7+δ (0≤x≤1) and systematically studied the evolution of various physical properties as a function of Er-doping. Our experimental studies, including X-ray diffraction (XRD), magnetic, X-ray absorption spectroscopy (XAS), X-ray photoelectron spectroscopy (XPS), heat capacity, and muon spin relaxation spectroscopy (μSR spectroscopy), revealed that while the Griffiths-like anomaly indeed disappears with doping at the macroscopic level, signatures of inhomogeneity are retained in ErBaCo4O7+δ too, at least at the local level. Overall, our results highlight the significant role of ionic radius and local structural distortions in stabilizing the Griffiths phase in this class of systems.