Highly nonlinear magnetoelectric effect in buckled-honeycomb antiferromagnetic Co4Ta2O9

High-spin Co3+ in cobalt oxyhydroxide for efficient water oxidation

Cobalt oxyhydroxide (CoOOH) is a promising catalytic material for oxygen evolution reaction (OER). In the traditional CoOOH structure, Co3+ exhibits a low-spin state configuration ([Formula: see text]), with electron transfer occurring in face-to-face [Formula: see text] orbitals. In this work, we report the successful synthesis of high-spin state Co3+ CoOOH structure, by introducing coordinatively unsaturated Co atoms. As compared to the low-spin state CoOOH, electron transfer in the high-spin state CoOOH occurs in apex-to-apex [Formula: see text] orbitals, which exhibits faster electron transfer ability. As a result, the high-spin state CoOOH performs superior OER activity with an overpotential of 226 mV at 10 mA cm-2, which is 148 mV lower than that of the low-spin state CoOOH. This work emphasizes the effect of the spin state of Co3+ on OER activity of CoOOH based electrocatalysts for water splitting, and thus provides a new strategy for designing highly efficient electrocatalysts.

Large magnetodielectric coupling in the vicinity of metamagnetic transition in 6Hperovskite Ba3GdRu2O9

The 6H-perovskites Ba₃RRu₂O₉(R = rare earth element) demonstrate the magnetodielectric (MD) coupling as a manifestation of 4d-4fmagnetic interactions. Here, a detailed study of the structural, magnetic, heat capacity, and MD properties of the 6H-perovskite Ba₃GdRu₂O₉is reported. The signature of long-range antiferromagnetic (AFM) ordering ∼14.8 K (T_N) is evident from the magnetization and heat capacity studies. TheT_Nshifts towards the lower temperature side, apart from splitting in two with the application of the magnetic field. Field-dependent magnetization at 2 K shows three metamagnetic transitions with the opening of small hysteresis in different regions. A new transition atT₁emerges after the onset of the first metamagnetic transition. Complex magnetic behavior is observed in different magnetic field regions whereas these field regions themselves vary with the temperature. Dielectric response recorded at zero and 80 kOe field exhibits the development of MD coupling well aboveT_N. The MD coupling (∼4.5% at 10 K) is enhanced by 25% as compared to the Dy counterpart. Effect of complex magnetic behavior is also conveyed in the MD results where the maximum value of MD coupling is observed in the vicinity of 10 K (onset ofT₁) and near the second metamagnetic transition. Our investigation suggests that both Gd and Ru moments align simultaneously atT_N. Short-range magnetic ordering is possibly responsible for MD coupling aboveT_N.