This work stands somewhat apart: its nearest neighbor in the archive is a study of magnetic resonance in chromium oxide, but thematically it aligns with a group of works on graphene, superconductivity, and quantum-like models. Around it, magnetic fans, hidden symmetries, and topological states in low-dimensional magnets have already been explored. However, Cu2(OH)3Br stands out for its rare combination of ferromagnetic and antiferromagnetic chains, where collective magnons and fractional spinons coexist. The question of how an external field rearranges these interacting subsystems remained open.
Single crystals of Cu2(OH)3Br were grown by the hydrothermal method. Magnetization was measured in static fields up to 14 T and pulsed fields up to 45 T at temperatures from 1.45 K. Terahertz spectroscopy was performed using a Martin–Puplett interferometer and a helium-3-cooled bolometer in fields up to 17 T, and up to 31 T with a Fourier spectrometer. Raman spectra were recorded with 515 nm laser excitation in fields up to 7 T. Radiation polarization was controlled by waveplates, and the magnetic field was applied along the three crystallographic axes.
For fields perpendicular to the chains (B∥a and B∥c*), spin-flop transitions occur at 5.4 T and 5.8 T, respectively, at which the excitation spectrum sharply rearranges: low-field modes disappear and new branches β, γ, δ appear. For fields along the chains (B∥b), no spin-flop occurs, but at a critical field of 16.3 T the ferromagnetic subsystem polarizes and the spectrum simplifies to a single broad mode κ that hardens with field. Raman spectroscopy revealed a magnon at 4 meV and a spinon continuum in the range 5–10 meV, as well as phonon modes. Upon crossing the Néel point (9.3 K), the magnon disappears while the spinon continuum persists up to high temperatures.
Unlike neighboring works that studied individual magnons or spinons in homogeneous systems, this study for the first time traces in detail the evolution of coexisting collective and fractional excitations across field-induced phase transitions in a coupled ferro-antiferromagnetic chain system. Polarization-resolved terahertz spectroscopy allowed separating the contributions of different subsystems and observing how their coupling weakens in strong fields. This provides direct experimental access to magnon-spinon interactions, which previously were only inferred from neutron data.
The topic could develop toward inelastic neutron scattering in magnetic fields to directly measure the excitation dispersion in disordered phases. It would also be interesting to investigate how spinons behave under dimensional reduction when the coupling between chains is broken. Theoretical models that include magnon-spinon interactions could be refined based on the obtained spectra.
The results will impact the physics of low-dimensional quantum magnets and the understanding of fractional excitations in strongly correlated systems.
Perform inelastic neutron scattering in magnetic fields above the critical values to measure the spinon spectrum in the disordered phase. Also, investigate the temperature dependence of excitations near the Néel point to look for signs of quantum criticality.
This work directly addresses the problem of coexistence and interaction of collective (magnon) and fractional (spinon) excitations in low-dimensional quantum magnets. It shows how an external field controls the balance between these two types of excitations, which is important for understanding quantum phase transitions and dimensional reduction in coupled chain systems.
This section is addressed to the author of the paper and their colleagues. Neighbouring works were found by meaning-based search across our archive, not by word overlap. We do not review: we show the field around the work.
What the work does
This work investigates the magnetic restructuring in the quasi-two-dimensional quantum magnet Cu2(OH)3Br with coexisting ferromagnetic and antiferromagnetic chains. Using terahertz and Raman spectroscopy, the evolution of magnons and spinons was tracked in fields up to 31 T at temperatures below the Néel point. Sharp spectral rearrangements were found at spin-flop transitions, along with a continuous evolution when the field is applied along the chains, indicating a weakening of the coupling between subsystems.
Where its strength is
The rare combination of ferromagnetic and antiferromagnetic chains provides direct experimental access to the interaction between collective and fractional excitations. Polarization-resolved terahertz spectroscopy made it possible to separate the contributions of different subsystems and to see how their coupling weakens in strong fields.
Where it could go next
Worth trying
Why this may matter
Understanding the interaction of magnons and spinons in coupled chain systems may clarify the mechanisms of phase transitions in low-dimensional quantum magnets and point to new functional capabilities of materials with coexisting subsystems.
Nearby works in our archive
The archive is sparse around this work: the closest review is only 0.55, against a usual 0.64. It looks like few have drilled nearby.
The crystal Cu2(OH)3Br is known as botallackite and was first described in 1948. Its structure resembles a ladder of copper ions, where ferromagnetic and antiferromagnetic 'rungs' alternate.