Combination of long range magnetic ordering, pressure-induced spin-crossover transition and light induced excited spin state trapping (LIESST) in a single cyanide-bridged FeNb compound has led to the first observation of a LIESST–based photo-magnetic effect under high hydrostatic pressure and low temperature. Under ambient pressure FeNb shows long range magnetic ordering at Tc = 9 K (ferrimagnetic) with large net magnetization (9.6 μB), magnetic hysteresis and relatively strong antiferromagnetic superexchange interactions between the high-spin FeII (S = 2) and NbIV (S = ½) centers: JFeNb = -3.1 cm-1 (H = -2.JFeNb.SFe.SNb). When the compound is subjected to high external pressure some of the FeII centers undergo spin-crossover transition and become diamagnetic (low-spin, S = 0) leading to the change of the magnetic ordering from ferrimagnetic to antiferromagnetic/metamagnetic at 5-10 kbar with large decrease of the magnetization below 9 K (Figure 1a). FeNb shows also a distinct piezochromic effect at room temperature (Figure 1b). Irradiation of the FeNb under 5-7 kbar using blue laser light (λ = 473 nm) results in the observation of an immediate spontaneous magnetization with critical temperature at ca. 8 K and magnetic hysteresis. Such a significant increase of magnetization is attributed to a photo-magnetic effect under pressure. It is fully reversible: heating to 50 K under 5-7 kbar restores the antiferromagnetic state and releasing the pressure restores the original long range magnetic ordering.

Multifunctionality at extreme conditions: spin cross-over photomagnetic behavior induced by pressure

249th National Meeting (2015)

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