Water, vacancies, and competing exchange interactions in Prussian blue analogues: a neutron diffraction study of field and dehydration-driven magnetic transitions
Abstract
We report a neutron diffraction study of the structural and magnetic properties of a family of ferro- and ferrimagnetic Prussian blue analogues (PBAs), A4[Fe(CN)6]2.7 (A = Co, Mn, Ni), Rb2Ni4[Fe(CN)6]3.3, and Mn4[Cr(CN)6]2.7, as a function of temperature (2--450~K) and applied magnetic field. All bimetallic compounds of the Fm3̅m family exhibit a broad diffuse feature at low scattering angle, which we identify, through comparison with the cation-stabilized Rb2NiFe framework, as an intrinsic signature of correlated vacancies and their associated interstitial water. High-temperature diffraction reveals a continuous crossover from positive to negative thermal expansion in CoFe and MnFe upon dehydration, while NiFe remains structurally robust up to 450~K. At low temperature, all compounds order in a collinear ferrimagnetic state with propagation vector k=(0,0,0), except MnFe, which adopts a partially frustrated magnetic structure with k=(1,0,0). A moderate magnetic field of Bc = 1.3~T drives a spin reorientation in MnFe toward the collinear k=(0,0,0) ferrimagnetic state common to the other compounds; the same transition is independently induced by dehydration. A minimal Heisenberg model shows that this transition results from a near-compensation between antiferromagnetic Mn--Fe coupling and a geometrically frustrated antiferromagnetic Mn--Mn interaction on the face-centered-cubic Mn sublattice, placing MnFe in the vicinity of a magnetic compensation point. These results resolve a longstanding ambiguity in the interpretation of the Fe K-edge XMCD response of MnFe-based PBAs, and establish water content as a key parameter controlling both the structural and magnetic stability of this family of materials, with direct relevance to their use as battery electrodes.
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BibTeX
@misc{dhami2026water,
title = {{Water, vacancies, and competing exchange interactions in Prussian blue analogues: a neutron diffraction study of field and dehydration-driven magnetic transitions}},
author = {N. S. Dhami and C. V. Colin and V. Nassif and O. Fabelo and T. Nait and A. Bleuzen and A. Bordage and V. Balédent},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.08976},
eprint = {2609.08976},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.08976},
note = {CC BY 4.0},
}
RIS
TY - UNPB
TI - Water, vacancies, and competing exchange interactions in Prussian blue analogues: a neutron diffraction study of field and dehydration-driven magnetic transitions
AU - N. S. Dhami
AU - C. V. Colin
AU - V. Nassif
AU - O. Fabelo
AU - T. Nait
AU - A. Bleuzen
AU - A. Bordage
AU - V. Balédent
PY - 2026
DA - 2026/09/08
PB - arXiv
DO - 10.48550/arxiv.2609.08976
UR - https://arxiv.org/abs/2609.08976
AB - We report a neutron diffraction study of the structural and magnetic properties of a family of ferro- and ferrimagnetic Prussian blue analogues (PBAs), A_4[Fe(CN)_6]_2.7 (A = Co, Mn, Ni), Rb_2Ni_4[Fe(CN)_6]_3.3, and Mn_4[Cr(CN)_6]_2.7, as a function of temperature (2--450~K) and applied magnetic field. All bimetallic compounds of the Fm3̅m family exhibit a broad diffuse feature at low scattering angle, which we identify, through comparison with the cation-stabilized Rb_2NiFe framework, as an intrinsic signature of correlated vacancies and their associated interstitial water. High-temperature diffraction reveals a continuous crossover from positive to negative thermal expansion in CoFe and MnFe upon dehydration, while NiFe remains structurally robust up to 450~K. At low temperature, all compounds order in a collinear ferrimagnetic state with propagation vector k=(0,0,0), except MnFe, which adopts a partially frustrated magnetic structure with k=(1,0,0). A moderate magnetic field of B_c = 1.3~T drives a spin reorientation in MnFe toward the collinear k=(0,0,0) ferrimagnetic state common to the other compounds; the same transition is independently induced by dehydration. A minimal Heisenberg model shows that this transition results from a near-compensation between antiferromagnetic Mn--Fe coupling and a geometrically frustrated antiferromagnetic Mn--Mn interaction on the face-centered-cubic Mn sublattice, placing MnFe in the vicinity of a magnetic compensation point. These results resolve a longstanding ambiguity in the interpretation of the Fe K-edge XMCD response of MnFe-based PBAs, and establish water content as a key parameter controlling both the structural and magnetic stability of this family of materials, with direct relevance to their use as battery electrodes.
ER -