When a metal-organic framework melts into glass, it becomes magnetic at room temperature, showing that atomic disorder can create magnetism in lightweight materials made from common elements.
(Nanowerk Spotlight) Magnetic materials sit quietly at the core of modern technology. They drive motors, store digital information, and guide the smallest sensors. Yet almost all rely on heavy, rigid compounds such as iron oxides or metallic alloys that are costly to process and difficult to adapt for flexible or lightweight applications.
Scientists working with metal organic frameworks (MOFs), have explored an alternative: magnets made from modular building blocks that can be chemically tuned almost like molecular construction sets. MOFs are composed of metal atoms linked by organic molecules, forming highly ordered lattices with large internal surface areas. Their structures can be tailored for uses that range from gas storage to catalysis.
None of these frameworks, however, managed to sustain magnetism at room temperature. The obstacle lies in their architecture. The organic linkers that connect the metal centers hold them too far apart, weakening the electronic interactions that align magnetic spins. When these interactions are weak, heat quickly randomizes the spins and the material becomes magnetically neutral.
Researchers tried strengthening the couplings by changing linkers, substituting heavier atoms, or embedding magnetic particles, but magnetism always disappeared as the temperature increased.
A different idea changes the physical state instead of the chemistry. Some MOFs can be heated until they melt and then rapidly cooled into glasses. When this happens, their ordered frameworks collapse into disordered networks. The atoms remain bonded but lose their repeating pattern. In this amorphous form, metal atoms can move closer together and their bond angles can shift.
These small rearrangements alter how unpaired electrons on neighboring metals interact, sometimes creating new routes for magnetic order. Disorder, in this case, becomes part of the design rather than a defect.
This concept has now been confirmed in a study published in Advanced Science (“Room‐Temperature Ferromagnetism in an Iron‐Based Zeolitic Imidazolate Framework Glass”). Researchers report that an iron based zeolitic imidazolate framework, when melted and quenched into glass, becomes weakly ferromagnetic at room temperature and remains magnetic up to 487 kelvin. The crystalline version of the same compound shows only antiferromagnetism, a state where neighboring spins cancel each other.
The finding shows that the transition from crystal to glass can generate magnetic behavior that does not exist in the ordered material, suggesting a path toward lightweight magnetic materials made from common elements.
Phase transitions and glass formation in an iron-based zeolitic imidazolate framework. A) Thermogravimetry (mass %) (red) and isobaric heat capacity (Cp) (black) curves of the as-synthesized Fe-ZIF crystal at the upscan rate of 10 K min−1. Inset: the glass transition in Fe-ZIF glass (Tg = 464 K). B) Schematic representation of structural evolution in Fe-ZIF during heating and melt-quenching (upper panel), along with optical images of the as-synthesized crystalline sample, the sample heated to 593 K, and the melt-quenched product (lower panel). (Image: Reprinted from DOI:10.1002/advs.202516465, CC BY) (click on image to enlarge)
The research focuses on an iron imidazolate compound written as Fe(Im)₂, where Im stands for imidazolate, a nitrogen containing molecule that links iron atoms. In its crystalline form, the framework contains a mix of tetrahedral and octahedral iron sites that determine how the metal bonds with nitrogen. The material was synthesized without solvent, heated to 705 kelvin until molten, and then cooled quickly to form a glass.
Measurements identified a glass transition at 464 kelvin, confirming that the product was a true amorphous solid. Microscopy showed smooth fracture surfaces typical of glass, and X ray diffraction confirmed the loss of long-range order.
Magnetic testing revealed a sharp contrast between the two states. At 300 kelvin, the crystal responded linearly to an applied magnetic field and showed almost no hysteresis, consistent with antiferromagnetism. Its Curie Weiss analysis gave a negative Weiss temperature of −27 kelvin, again indicating antiferromagnetic coupling between iron centers.
The glass, by contrast, displayed a clear hysteresis loop with a coercive field of 510 oersted and a remanent magnetization of 0.38 electromagnetic units per gram. The loop remained open even at ±20 000 oersted, which is typical of weak ferromagnetism where spins are not perfectly opposed but slightly tilted. The magnetic order persisted up to 487 kelvin, confirming that it was intrinsic and thermally stable.
Weak ferromagnetism arises when spins that usually cancel are canted at a small angle, leaving a residual magnetization. This canting often results from an asymmetric exchange called the Dzyaloshinskii–Moriya interaction, which appears when local symmetry around magnetic atoms is broken. Glasses naturally lack symmetry at the atomic level, making such effects possible. To uncover the mechanism, the researchers combined computer modeling with several spectroscopic methods.
Density functional theory, a quantum mechanical modeling approach, examined small fragments of the Fe–imidazolate network. The calculations showed that in the ordered crystal, the first and second neighboring iron atoms couple antiferromagnetically through the imidazolate bridges, with exchange energies of −1.5334 and −0.4040 millielectronvolts. A third pair more than seven angstroms apart interacts only weakly. This pattern favors antiparallel spin alignment in the crystal. For the glass to display ferromagnetism, these couplings must become unbalanced through structural distortion or changes in spin state.
Spectroscopic data support this picture. X ray photoelectron spectra confirm that iron remains in the +2 oxidation state throughout, ruling out redox effects. Raman spectra, which track vibrations of iron–nitrogen bonds, show that the crystal contains both high spin and intermediate spin sites. When heated to form an intermediate phase, the iron centers shift to low spin states with fewer unpaired electrons.
In the glass, the spectra indicate a return to uniform high spin Fe²⁺, where each iron atom carries several unpaired electrons that strengthen magnetic coupling. Mössbauer spectroscopy, which senses the local environment of iron nuclei, confirms this transformation. The crystal contains two types of sites, the intermediate phase shows two low spin signals, and the glass displays a single high spin signal with consistent parameters. The uniform high spin state increases local magnetic moments and enhances overall exchange interactions.
Further structural analysis using high energy X ray pair distribution functions shows that the average iron to iron distance contracts from 6.20 to 6.00 angstroms during vitrification. A reduction of 0.20 angstrom increases orbital overlap between neighboring iron atoms through the imidazolate bridges. Shorter distances strengthen magnetic exchange, while the absence of symmetry removes the restriction that previously forced spins to oppose one another. These combined changes produce a slightly canted spin arrangement that generates weak ferromagnetism.
Thermal analysis clarifies how this transformation unfolds. Between 480 and 571 kelvin, the crystalline framework loses some imidazolate molecules, converting part of the structure into corner sharing tetrahedra. Even after this step, the material remains antiferromagnetic up to 593 kelvin. Only when it melts and solidifies into a glass does the magnetic state change to ferromagnetic. This sequence identifies structural disorder as the key factor, not ligand loss alone.
At a practical level, the measured properties are significant. The coercivity of 510 oersted and the critical temperature of 487 kelvin indicate stable magnetic domains that function well above room temperature. The unsaturated magnetization loop implies many small domains that are weakly coupled, typical of canted antiferromagnets. Such materials could support compact data storage, magnetic sensors, and low power switching devices. Because framework glasses are light, moldable, and chemically tunable, they can be processed into thin films or patterned components more easily than traditional magnetic solids.
In plain terms, the study links structure, spin state, and atomic spacing. The iron framework changes from a crystal where spins cancel each other to a glass where shorter distances and uniform high spin states allow the spins to tilt slightly. That tilt creates a measurable magnetic moment that remains stable at normal conditions. All experimental and theoretical observations fit this mechanism.
The result challenges the assumption that atomic order is required for magnetism. It shows that controlled disorder can stabilize magnetic behavior in materials made from abundant elements and flexible chemistry. By clarifying how spin state and structure interact in a glassy network, the work outlines a strategy for designing new magnetic frameworks that operate at room temperature. These materials could expand the options available for spintronic and sensing technologies while using lighter and more adaptable compounds than conventional magnets.
For authors and communications departmentsclick to open
Lay summary
Prefilled posts
Nanowerk Newsletter
Get our Nanotechnology Spotlight updates to your inbox!
Thank you!
You have successfully joined our subscriber list.
Become a Spotlight guest author! Join our large and growing group of guest contributors. Have you just published a scientific paper or have other exciting developments to share with the nanotechnology community? Here is how to publish on nanowerk.com.
