Magnetic Transitions in Irradiated CrSBr: Resonant Raman Scattering ✛
Context
Layered CrSBr has attracted attention as a platform for quantum technologies due to the strong anisotropy of its magnetic, electronic, and optical properties. Within each layer it is ferromagnetic, while between layers it is antiferromagnetic, with a Néel temperature of about 132 K. Controlling magnetic phases typically requires external fields or complex methods. Ion irradiation offers a route to permanently modify exchange interactions through defect creation, but reliably identifying the resulting phases remains a challenge, especially for thin flakes. This work fits into a line of research where irradiation and optical methods are applied to magnetic van der Waals materials, but it emphasizes polarization-resolved Raman scattering as a sensitive probe.
Methods
CrSBr crystals were grown by chemical vapor transport and exfoliated onto SiO2/Si substrates. Samples were irradiated with helium ions at energies of 8 and 1 keV, with doses chosen for a uniform damage profile (DPA 0.01 and 0.02). Temperature-dependent polarization-resolved Raman spectroscopy was performed with 1.96 eV excitation over the range 4–200 K with an angular resolution of 4°. Magneto-optical measurements were carried out at 4.7 K in a vector magnet with the field along the b-axis. Analysis of polar intensity dependences allowed extraction of the Raman tensor components.
Results
In pristine CrSBr, the b-component of the Raman tensor shows a sharp jump at 132 K—the transition to the antiferromagnetic phase. In irradiated samples, two dips are observed: around 40 K (TD) and 105–110 K (TC). The transition at TC is attributed to the establishment of modified antiferromagnetic or ferromagnetic order from the paramagnetic state. The transition at TD likely arises from ferromagnetic ordering of defects, spin freezing, or an anisotropy crossover. The magnitude of the anomalies increases with irradiation dose and decreases with sample thickness. Magneto-optics shows that a single irradiation weakens antiferromagnetic order, while double irradiation in the bulk region leads to a fully ferromagnetic state with no field response.
Implications
This work demonstrates that polarization-resolved Raman spectroscopy is sensitive to changes in the scattering tensor induced by magnetic ordering and can distinguish transitions invisible in phonon frequency spectra. Unlike neighboring studies that used magnetometry or neutron scattering, here a fast, non-destructive optical method applicable to thin flakes is proposed. This expands the toolkit for studying defect-engineered magnetic phases in two-dimensional materials.
Future development
Further research could focus on elucidating the nature of the transition at 40 K—for example, through spin dynamics measurements or local probing of defects. A systematic study of the dependence of magnetic phases on ion type and energy, as well as layer thickness, is also possible. Further development of the method will enable real-time tracking of magnetic transitions under changing external conditions.
Impact
The results are important for spintronics and quantum technologies, where precise control of magnetic states in low-dimensional materials is required. The method can be extended to other layered magnets.
Next steps
A detailed investigation of the microscopic mechanism of the transition at 40 K is planned, involving additional techniques. Irradiation parameters will also be optimized to achieve targeted magnetic phases.
Key open problems
The nature of the low-temperature transition in irradiated CrSBr remains an open question: it may be related to ferromagnetic ordering of defects, spin freezing, or changes in magnetic anisotropy. This resonates with the broader problem of understanding the role of defects in the magnetism of two-dimensional materials.
The knowledge machine's view
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
The authors irradiated layered CrSBr with helium ions and, using polarization-resolved Raman spectroscopy, detected two magnetic transitions at ~40 K and 105–110 K, associated with defect-engineered phases. Magneto-optical measurements confirmed the suppression of antiferromagnetic order and the emergence of a ferromagnetic state at high doses.
Where its strength is
The strength of the work lies in the fact that the polarization-resolved Raman signal proved sensitive to changes in the scattering tensor at magnetic transitions, allowing discrimination of phases invisible in phonon frequency spectra. This provides a fast, non-destructive optical method for probing defect-engineered magnetic states in thin layers.
Where it could go next
- It might be interesting to compare the observed magnetic transitions with results from studies on switching magnetic states via guest molecules, which also explore controlling magnetic order through external stimuli.based on: How Guest Molecules Flip a Magnet arXiv:2602.20940
- A related approach uses local optical probes to visualize magnetic textures; adapting such methods could map defect-engineered phases in CrSBr with high spatial resolution.based on: Tiny Beacons Inside a Magnet arXiv:2601.17516
- Exploring the connection between irradiation-induced defects and transport properties, as in work on magnetoresistance in graphene heterostructures, could complement understanding of how defects affect electronic states.based on: Magnetic resistance in a graphene sandwich arXiv:2608.11389v1
Worth trying
- Test whether the observed transitions persist in samples with different irradiation doses and ion energies.
- Apply polarization-resolved Raman spectroscopy to other layered magnetic materials modified by irradiation to check the method's universality.
- Correlate temperature-dependent Raman response with magnetometry and neutron scattering data to clarify the nature of the phases at 40 K and 105–110 K.
Why this may matter
Developing methods to control magnetic phases in two-dimensional materials is important for spintronic devices and quantum technologies, where local manipulation of magnetic order without external fields is required.
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Original abstract
as written by the authors arXiv:2608.18909v1
Controlling magnetic phases and accurately determining their transition temperatures are essential for the development of low-dimensional magnetic materials. Here, we demonstrate that He$$^+$$ ion irradiation provides a versatile route for engineering magnetic phases in layered CrSBr and establish temperature-dependent polarization-resolved Raman spectroscopy as a sensitive optical probe for identifying irradiation-induced magnetic phase transitions. We reveal that the magnetic response of the modified CrSBr is governed by both irradiation dose and crystal thickness. The temperature evolution of the Raman tensor elements resolves the antiferromagnetic transition in pristine CrSBr at T$$_N \approx 132$$ K as well as irradiation-induced magnetic transitions at T$$_C \approx 105-110$$ K and T$$_D \approx 40$$ K corresponding to ferromagnetic and defect-related magnetic phase transitions. Complementary magneto-optical measurements confirm the progressive suppression of antiferromagnetic order and the emergence of new defect-engineered magnetic phases, including pure ferromagnetic behavior at high irradiation doses. These findings establish irradiated CrSBr as a platform for controllable magnetic phase engineering while demonstrating polarization-resolved Raman spectroscopy as a rapid, non-destructive, and broadly applicable method for probing magnetic phase transitions in van der Waals magnets.
The helium ions used for irradiation are the same alpha particles emitted during radioactive decay, but here they serve as a tool for precise material modification.
The idea of controlling material properties via irradiation echoes science fiction plots where radiation alters matter, yet here the process is controlled and reproducible.
Key numbers
- Néel temperature of pristine CrSBr: 132 K
- Transition temperature TC in irradiated samples: 105–110 K
- Transition temperature TD in irradiated samples: 40 K
- Excitation energy for Raman spectroscopy: 1.96 eV
- Irradiation dose (single): 3.8×1013 – 1.5×1014 cm^-2