Quantum Ferromagnets Without the Usual Tricks: Unraveling the True Nature of Magnetism

Iron pyrite crystal structure illustrating quantum ferromagnetic behavior

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For nearly a century, physicists have tried to unravel one of the deepest puzzles in condensed matter science: what really causes magnetism? From refrigerator magnets to magnetic memories and superconductors, the interplay of electrons that gives rise to magnetic order is still not completely understood. A recent study challenges long-standing assumptions by revealing that purely quantum mechanical effects within electrons themselves — without any help from the atomic lattice — can explain complex magnetic behavior previously attributed to lattice vibrations or spin–phonon coupling.

This research, reported by Lorna Brigham for Physics World and detailed in the paper “Magnon Damping and Mode Softening in Quantum Double-Exchange Ferromagnets” (Rep. Prog. Phys. 88 068001, 2025), represents a significant step toward understanding the true quantum origins of ferromagnetism.

Rethinking Magnetism: The Quantum View

Traditionally, magnetic materials are described as systems where localized electrons on atoms carry tiny magnetic moments (spins), while mobile conduction electrons move through the crystal. The interaction between these two populations of electrons — one fixed, one itinerant — gives rise to “double-exchange” ferromagnetism. This mechanism explains how materials such as manganites can become magnetic and exhibit spectacular effects like colossal magnetoresistance, where electrical resistance changes dramatically under a magnetic field.

However, experimental results over the past two decades have revealed several anomalies that classical models cannot explain. Using techniques like neutron scattering, scientists have observed that the collective spin waves (known as magnons) in these materials do not behave as expected. Their characteristic energies soften (decrease), and their sharp, well-defined peaks blur into diffuse continua — as if the magnons are losing their coherence.

Previously, such effects were blamed on phonons — vibrations of the crystal lattice — or on complicated couplings between spin, charge, and orbital motion. But new simulations show that these “usual tricks” are not necessary to explain the mystery. The strange magnetic dynamics can emerge naturally from the quantum nature of the spins themselves.

Quantum Spins Take Center Stage

The international research collaboration — including Adriana Moreo and Elbio Dagotto (University of Tennessee, USA), Takami Tohyama (Tokyo University of Science, Japan), and Marcin Mierzejewski and Jacek Herbrych (Wrocław University of Science and Technology, Poland) — took a fully quantum mechanical approach. Instead of treating spins as classical “arrows,” the team modeled them as true quantum entities capable of fluctuation, entanglement, and superposition.

Using two powerful frameworks — a quantum Kondo lattice model and a two-orbital Hubbard model — the researchers simulated how electrons and spins interact without any semiclassical approximations. Their results reveal a fascinating dual behavior of the electronic system:

The interaction between magnons and this incoherent continuum naturally explains why magnons lose coherence and energy — a phenomenon long observed in experiments but never fully understood until now.

Magnons Meet Quantum Decoherence

The simulations show that as magnons propagate through the quantum material, they scatter off the fluctuating local triplet excitations near the Fermi level. This process creates a Stoner-like continuum of spin excitations — a kind of quantum background “buzz” — that damps the magnons and leads to energy softening. Importantly, this damping is purely electronic in origin. No lattice vibrations or phonon interactions are required.

This finding challenges decades of theoretical models and opens a new chapter in the study of magnetism. It implies that quantum decoherence of spin waves is an intrinsic property of certain electronic systems, not a side effect of structural imperfections or thermal noise.

Beyond Manganites: Implications for Quantum Materials

While the study focuses on manganite-like systems, its implications are far broader. Similar mechanisms could operate in iron-based superconductors, ruthenates, and heavy-fermion compounds — all systems where magnetic order and superconductivity coexist or compete. Even in materials without permanent magnetic moments, strong electronic correlations can generate emergent magnetism with similar quantum characteristics.

This purely electronic mechanism could also help scientists design new quantum ferromagnets and exotic materials where magnetism can be tuned by controlling electron correlations instead of lattice distortions. The discovery bridges the gap between quantum magnetism, spintronics, and correlated electron physics, pointing to potential applications in high-performance magnetic memory and quantum computation devices.

From Classical Spins to Quantum Entanglement

The work represents a conceptual shift in how magnetism is understood. By discarding the classical approximation and fully embracing the quantum behavior of localized spins, researchers have shown that the electron’s quantum personality alone is sufficient to produce complex magnetic dynamics. This realization could help unify the theoretical frameworks describing magnetism, superconductivity, and correlated electron behavior.

“Our study reveals that quantum effects intrinsic to the spin system can explain the anomalies seen in experiments,” says co-author Elbio Dagotto. “It’s a purely electronic mechanism — no need to invoke lattice vibrations or external perturbations.”

Quantum Ferromagnetism Reimagined

These insights not only deepen our understanding of magnetism but also mark an exciting step toward engineering quantum materials that operate on principles of coherence, entanglement, and intrinsic quantum disorder. The ability to model and predict such effects paves the way for developing next-generation spintronic devices and even quantum magnets for information processing.

By bringing quantum mechanics to the heart of ferromagnetism, researchers are rewriting a story that began nearly a century ago — proving that even one of physics’ oldest mysteries can still surprise us with new quantum layers.

Original article source: Physics World – “Quantum Ferromagnets Without the Usual Tricks” (November 2025).

This blog article was prepared with the help of AI technologies to enhance accessibility and public understanding of scientific research.

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