Evidence for complex multistability in photomagnetic cobalt hexacyanoferrates from combined magnetic and synchrotron x-ray diffraction measurements

Abstract

Cobalt hexacyanoferrates, which exhibit thermally induced and photo-induced spin transitions, have been extensively studied as model materials for molecular-based photomagnetic solids. Synchrotron x-ray diffraction ͑XRD͒ experiments combined with magnetic measurements were used here to get some new insights in their diagram of phase transformation. For a Na 0.32 Co͓Fe͑CN͒ 6 ͔ 0.74 · 3.4H 2 O sample composition, the hightemperature ͑HT͒ phase could be efficiently trapped by rapid cooling, thus allowing a comparison with the photo-induced phase directly formed at low temperature by light irradiation. In terms of magnetic behavior, the two metastable phases strongly differ with lower critical temperature and magnetization values but higher decay temperature for the HT quenched phase. As only a slight change in the lattice constant with no symmetry breaking is reported from XRD, the differences between the two phases are discussed on the basis of local and disordered tilting of the ͓Fe͑CN͒ 6 ͔ polyhedral units.

Metastable state of the photomagnetic Prussian blue analog K0.3Co[Fe(CN)6]0.77Chong1, Itoi2, Boukheddaden3 et al. 2011Phys. Rev. BSelf Cite250200View full textAdd to dashboardCite

“…The present data for the Q and LTPX states qualitatively agree with the previous observations made for the Na-compound 10 . The Q state possesses a lower T C , a higher T relax and a smaller M s values for comparable HS fraction.…”

“…A possible explanation is based on the structural data reported in Ref. 10, which shows that the Q state undergoes an electronic relaxation towards a "Q-relaxed" state prior to the structural relaxation towards the LT state. The cooperativity associated with this latter transformation is missing during the electronic transformation observed by magnetic measurements.…”

“…Short-range structural modifications in A x Co[Fe(CN) 6 ] y · zH 2 O (A: alkali metal) PBAs were observed in 1998 by EXAFS 8,9 , but complete analysis of the long-range aspects remain to be investigated. These structural modifications are obviously involved in the multistability previously reported for some PBAs 10 , and might play a key role in the control of the photo-induced magnetic phases.…”

Microscopic Origin for Multistability in a Photomagnetic CoFe Prussian Blue Analogue

“…[5,6] The control of the switching properties of these compounds can be chemically achieved by introducing or replacing counterions, solvent, or guest molecules. [13,14] In this paper, we compare the thermally populated and photoinduced states of the Na 2 Co 4 [Fe(CN) 6 ] 3.3 ·14H 2 O Prussian blue analogue (PBA) (labeled Na 2 CoFe in the following). While some studies point out symmetry breaking in spin transition sys- [ tems, [9][10][11][12] some other structural distortions remain unexplained in switchable coordination networks.…”

“…However, the existence of multistability in closed switchable systems made of crystallographically equivalent switching sites remains a controversial topic. While some studies point out symmetry breaking in spin transition systems,9–12 some other structural distortions remain unexplained in switchable coordination networks 13,14…”