Pressure induced switching of magnetic interaction and magneto-barocaloric effect in a cobalt(II)-niobium(IV) molecular ferromagnet.

This proposal seeks to examine pressure-induced changes in the magnetic properties of the 3D coordination polymer {[CoII(pyrazole)4]2[NbIV(CN)8]·4H2O}n, a soft ferromagnet below Tc = 5 K. Magnetic measurements under pressure show a Tc decrease to 3.5 K at 0.3 GPa, followed by a reversal to 5.1 K at 1.2 GPa. Conversely, magnetization declines consistently across the pressure range, indicating a potential modification of magnetic ordering. Magneto-barocaloric effect measurements reveal a significant entropy change tied to pressure variations. Single-crystal X-ray diffraction identifies structural modifications and a phase transition near 0.4 GPa. To investigate how external pressure alters magnetic properties and to elucidate the magneto-barocaloric effect, we propose XAS/XMCD measurements at the Nb L2,3 edges at 2.0–3.0 K under applied pressures of 0.25, 0.5, and 1.3 GPa, using a diamond anvil cell at ESRF ID12—the only beamline worldwide capable of probing these edges.