Low magnon damping of a EuSe film down to millikelvin temperatures

arXiv:2610.21733 · cond-mat.mtrl-sci, cond-mat.mes-hall · Submitted 2026-10-15 · Read on arXiv

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Introduction to the show: ident: Quantum Radio. Generated commentary on the latest quantum physics and condensed matter papers.

Kai: Today's paper: "Low magnon damping of a EuSe film down to millikelvin temperatures".

Mira: The gist: The intrinsic ferromagnetic resonance (FMR) linewidth of an epitaxial EuSe film on a diamagnetic BaF2 substrate decreases upon cooling,

Kai: First, who's behind it and why it matters.

Title and authors: Kai: So we're talking about this paper now, "Low magnon damping of a EuSe film down to millikelvin temperatures". We're looking at how magnetic losses in these materials behave when you get really cold.

Mira: Yeah, it’s interesting because europium chalcogenides are already considered promising candidates for magnonics, but understanding the intrinsic damping mechanism is still pretty fuzzy.

Lev: From an error correction standpoint, low loss is critical because thermal noise and dissipation can really kill the fidelity of any quantum operation we try to do.

Kai: Exactly. This paper characterizes an epitaxial film of metamagnet EuSe on a diamagnetic BaF2 substrate using both magnetometry and broadband ferromagnetic resonance measurements down to thirty millikelvin <ref:2610.21733#pg2>.

Mira: And what they found is that the intrinsic linewidth of the ferromagnetic resonance decreases as you cool it down, and then it actually becomes temperature independent at high frequencies up to seven hundred fifty millikelvin <ref:2610.21733#pg3>.

Lev: That suggests low magnon damping in this material, which is a key parameter for its application in quantum magnonics.

Kai: They found that the linewidth also decreases with increasing frequency and increasing magnetic field, which is a behavior we see when we compare it to some of the standard ferromagnetic materials.

Mira: And at thirty millikelvin, they measured a resonance field of one thousand twenty-eight milliTesla corresponding to a magnon lifetime of two nanoseconds and an upper bound for the Gilbert damping parameter of one point one times ten to the minus three <ref:2610.21733#pg3>.

Lev: So that two nanosecond lifetime is a specific number we can actually work with when designing our hardware, which is good information.

Kai: What's really striking is that this behavior is consistent with a magnon lifetime of two nanoseconds, which gives us some concrete numbers to use.

Mira: They also pointed out that the linewidth below the Néel temperature TN decreases as frequency increases and levels off above about forty-five gigahertz <ref:2610.21733#pg3>.

Lev: That leveling off suggests there’s an intrinsic limit to how much damping we can expect in this regime, which helps us set expectations for real-world implementation.

Title and authors: Kai: When we look at how this compares to other materials, they found that the linewidth of the field-aligned film decreases with increasing frequency and field.

Mira: The diamagnetic BaF2 substrate eliminates a stray-field mechanism that you often have to deal with in other systems, like YIG, which is a big advantage.

Lev: That lack of damping increase down to thirty millikelvin on the BaF2 substrate rules out the mechanism that dominates low-temperature damping in YIG films on paramagnetic garnets <ref:2610.21733#pg2>.

Kai: The paper also found that the residual linewidth at high fields, which doesn't depend neither on temperature nor frequency, is consistent with an inhomogeneous distribution of local resonance fields.

Mira: So they conclude that this residual broadening is extrinsic rather than being caused by thermally populated magnons or temperature-dependent scattering processes.

Lev: That means the main source of loss isn't what you can easily control just by cooling things down, which simplifies our noise budget analysis significantly.

Kai: The paper states that the effective magnetization equals the full spin-only moment at high temperatures, where the resonance is that of paramagnons of the field-polarized paramagnetic phase.

Mira: That points toward a material behavior where you can leverage paramagnon properties in this specific regime for your quantum applications.

Lev: So, if we look at how they analyzed the data, it seems they determined that an upper bound for the Gilbert damping parameter is one point one times ten to the minus three by using measured linewidths at sixty-eight gigahertz and thirty millikelvin which are reported as five point five milliTesla corresponding to a magnon lifetime of two nanoseconds <ref:2610.21733#pg3>.

Kai: That connection between those specific measurements and the resulting upper bound is pretty direct, which is helpful for validating our own models.

Mira: They also suggested that the effective magnetization equals the full spin-only moment at high temperatures, where the resonance is that of paramagnons of the field-polarized paramagnetic phase.

Kai: They also suggested that this behavior is consistent with a magnon lifetime of two nanoseconds, which is a specific number we can actually work with when designing our hardware.

Title and authors: Kai: They also found that the intrinsic linewidth approaches a constant value above about forty-five gigahertz, which they link to a magnon lifetime of two nanoseconds <ref:2610.21733#pg3>.

Mira: This suggests that above that frequency, the damping doesn't change much anymore because you're hitting some fundamental limit in this material.

Lev: That suggests that we can focus our error correction efforts on operating within those specific frequency bands where the damping is most predictable.

Kai: They also mentioned comparing a five hundred nanometer film to a two hundred forty nanometer film, and that the linewidth of the five hundred nanometer film exceeds that of the two hundred forty nanometer film in common frequency ranges by a factor of one point one to one point nine at equal temperatures <ref:2610.21733#pg3>.

Mira: This comparison helps establish that the decrease with frequency is observed in two EuSe films of different thickness, which confirms it's a property of EuSe films rather than just some specific sample setup.

Kai: They also found that the intrinsic linewidth decreases with increasing frequency and field, which is a characteristic of this material compared to other Gilbert-damped ferromagnets.

Mira: And because they saw that no significant strain is present in the film, it suggests both transition fields, BT and AFM to FiM transition field follow the phase diagram within ten milliTesla.

Lev: That lack of significant strain is a good thing because strain can introduce extra scattering channels that we have to model when we try to design our devices.

Kai: Overall, this paper on "Low magnon damping of a EuSe film down to millikelvin temperatures" points toward using these materials as a versatile platform for quantum magnonics and spintronics.

Mira: It seems like they’ve provided some really solid constraints on the intrinsic losses that we need when designing these systems.

Kai: So, this research on "Low magnon damping of a EuSe film down to millikelvin temperatures" gives us a clearer picture of how we can engineer these systems for lower dissipation.

Mira: It really does provide some solid constraints on the intrinsic losses that we need when designing these systems.

Lev: And for us, it means we have better parameters to include in our error correction overhead calculations.

The paper's summary: Kai: So, to recap, this paper looked at how magnetic losses in an epitaxial film of europium selenide behave when you cool it down to thirty millikelvin temperatures and found that the intrinsic damping stays very low.

Mira: Exactly what they found is that the internal friction, or magnon damping, decreases as you lower the temperature and also as you increase the frequency of your resonance.

Lev: That low damping is important because when we’re building quantum devices, we need things to stay coherent for a long time; this suggests EuSe has some good properties for that.

Kai: They measured that at thirty millikelvin, they got a resonance field of one thousand twenty-eight milliTesla which corresponds to a magnon lifetime of two nanoseconds.

Mira: And the authors used those measurements to get an upper bound for the Gilbert damping parameter, which is about one point one times ten to the minus three.

Lev: Two nanoseconds lifetime is a concrete number we can actually use in our error correction overhead calculations, so that's solid info for us.

Kai: They also pointed out that this behavior is consistent with that two nanosecond lifetime they measured, which gives us some specific numbers to work with.

Mira: They noted that the intrinsic linewidth approaches a constant value above about forty-five gigahertz, which suggests there’s an intrinsic limit to how much damping we can expect in that frequency range.

Lev: That leveling off means for frequencies above forty-five gigahertz, you don't need to worry about temperature changing the loss as much.

Kai: They also found that when they compared a five hundred nanometer film to a two hundred forty nanometer film, the linewidth of the longer one was bigger by about one point one to one point nine at equal temperatures.

Mira: That comparison shows that it’s not just some fluke for one sample; the decrease in linewidth with frequency actually holds true for EuSe films of different thicknesses.

Lev: That confirms it's a property of the material itself, not just how we made this specific film, which is good for scaling up our hardware designs.

Kai: They also saw that because there’s no significant strain in the film, both the transition field to antiferromagnetic and from antiferromagnetic to ferrimagnetic phases happen within ten milliTesla.

Mira: That lack of strain is a nice thing because strain can introduce extra scattering channels that we have to model when we try to design our devices.

Lev: So, if you look at how they analyzed the data, they determined that this residual broadening at high fields doesn't depend on temperature or frequency; it’s consistent with an inhomogeneous distribution of local resonance fields.

Kai: That means the extra width we see isn't from thermally excited magnons, which simplifies our noise budget analysis a lot.

Mira: They concluded that this remaining broadening is extrinsic, meaning it comes from other things besides the intrinsic material properties they were measuring directly.

Lev: That’s good because it means we can focus our error correction efforts on controlling those specific local field variations instead of just fighting general thermal noise.

Kai: The paper states that at high temperatures, the effective magnetization equals the full spin-only moment, which means the resonance is actually coming from paramagnons in that field-polarized phase.

Mira: That points toward a material behavior where you can leverage those paramagnon properties in this specific regime for your quantum applications.

Lev: So, if we look at how they analyzed the data, they determined that an upper bound for the Gilbert damping parameter is one point one times ten to the minus three by using measured linewidths at sixty-eight gigahertz and thirty millikelvin which are reported as five point five milliTesla corresponding to a magnon lifetime of two nanoseconds.

Kai: That connection between those specific measurements and the resulting upper bound is pretty direct, which is helpful for validating our own models.

Mira: They also suggested that this behavior is consistent with a magnon lifetime of two nanoseconds, which gives us some concrete numbers to use when designing our hardware.

Lev: That suggests that above forty-five gigahertz, the damping doesn't change much anymore because you're hitting some fundamental limit in this material.

Kai: So, this research on low magnon damping of a EuSe film down to millikelvin temperatures gives us a clearer picture of how we can engineer these systems for lower dissipation.

Mira: It really does provide some solid constraints on the intrinsic losses that we need when designing these systems.

Lev: And for us, it means we have better parameters to include in our error correction overhead calculations.

The paper's improvements: Kai: So, we've heard about the paper showing low intrinsic damping in EuSe films down to thirty millikelvin temperatures, and now we're looking at what they suggest for making this even better.

Mira: They look at how they can use the data from two different film thicknesses to get a more accurate picture of the frequency dependence.

Lev: That comparison is useful because it helps confirm that the damping decreases with frequency across different sample sizes, which strengthens their case that it’s a material property and not just some random setup artifact.

Kai: They are using this thickness comparison to better predict those intrinsic linewidth values, which is key because we need reliable numbers for our modeling.

Mira: That gives us a way to get a more precise estimate of the Gilbert damping parameter, which they say provides an upper bound of one point one times ten to the minus three.

Lev: An upper bound is helpful, but what matters for real hardware is that it tells us the maximum overhead we need to plan for in our error correction schemes.

Kai: They also confirm that their analysis points toward extrinsic loss mechanisms being responsible for the residual broadening at high fields, which means we don't have to worry as much about thermal noise dominating low-temperature damping.

Mira: That’s a big deal because if we can isolate the intrinsic loss from the extrinsic stuff, it tells us exactly what fundamental limits are on this material.

Lev: It simplifies our design process because we can focus on engineering away those specific extrinsic effects instead of trying to fix general thermal scattering everywhere.

Kai: They also look at how they can map out magnetic phase transitions by analyzing the field and temperature dependence of the metamagnetic steps in EuSe.

Mira: That phase diagram mapping is important because it shows how fields below zero point two five tesla switch the material between different magnetic states, like antiferromagnetic, ferrimagnetic, and ferromagnetic phases.

Lev: Having a clear map of those transitions helps us understand the magnetic landscape we’re working with when designing hybrid quantum systems.

Kai: By understanding this phase diagram, we can better choose our operating points for maximum coherence.

Mira: So, they are suggesting that this material is a versatile platform because it has these controllable magnetic phases and low intrinsic losses across a wide frequency range.

Conclusion: Kai: So, to wrap up this paper on "Low magnon damping of a EuSe film down to millikelvin temperatures," we found that EuSe is promising for quantum magnonics because the intrinsic losses are very low at these cold temperatures.

Mira: Right, it really shows that if you choose your material carefully, you can get some predictable behavior where the loss doesn't explode as you cool things down.

Lev: For hardware design, knowing that the damping parameter is bounded by one point one times ten to the minus three gives us a solid starting point for our error correction overhead calculations.

Kai: They’ve shown that this material offers a zero-field state without any net moment or stray field, which is exactly what we want for building stable quantum systems.

Mira: And they identified that the residual broadening we see at high fields is extrinsic, which means it isn't caused by thermally excited magnons at all.

Lev: That’s good because it simplifies our noise budget analysis a lot; we can focus on controlling those specific local field variations instead of fighting general thermal scattering everywhere.

Kai: Overall, this work gives us concrete numbers for the intrinsic linewidth and tells us that EuSe can be a versatile platform for spintronics and quantum magnonics.

Mira: It’s important because it sets clear expectations for how much dissipation we should actually anticipate when we start building devices with these materials.

Lev: From an error correction standpoint, knowing the magnon lifetime is around two nanoseconds means we have a specific timescale to work within for our qubit operations.

Kai: So, the main thing here is that EuSe has this low intrinsic damping across a broad range of frequencies and temperatures.

Mira: That’s what really matters because it moves us closer to using these materials reliably in quantum hardware.

Lev: We still have to figure out how to scale up the growth of these epitaxial films without introducing too much strain or defects.

Kai: Next time, we’re going to look at how this low loss compares when we introduce other magnetic materials or maybe explore a different way to engineer the film structure itself.

Rostyslav O. Serha, Jan Hofer, Khrystyna O. Levchenko, Andreas Ney, Sergej O. Demokritov, Gunther Springholz, §Andrii V. Chumak

Faculty of Physics, University of Vienna · Institute of Semiconductor and Solid State Physics, Johannes Kepler University Linz · Institute of Applied Physics, University of Münster

cond-mat.mtrl-sci, cond-mat.mes-hall

Submitted: 2026-10-15

Updated: 2026-10-15

License: http://creativecommons.org/licenses/by/4.0/

Importance score: 91/100

The gist: The gist: The intrinsic ferromagnetic resonance (FMR) linewidth of an epitaxial EuSe film on a diamagnetic BaF2 substrate decreases upon cooling, becomes temperature independent at high frequencies

Key concepts

Intrinsic FMR Linewidth: This is the fundamental width of the magnetic resonance peak in the material itself. It is measured by analyzing how the signal dip changes with frequency and field. A decrease in this linewidth as you increase frequency or field indicates low magnon damping, meaning energy loss through spin waves is minimal.
Magnon Damping: Magnon damping refers to the process where spin waves (magnons) lose energy and decay over time. Low damping is crucial for quantum applications because it means the magnons can persist for a long time, allowing them to carry quantum information without rapidly losing coherence.
Zero-Field State: EuSe exhibits a unique state below its Néel temperature where it has no net magnetic moment and no stray field. This property is highly desirable in quantum systems as it eliminates external magnetic interference, making the material an attractive platform for hybrid quantum devices.
Gilbert Damping Parameter: This parameter quantifies how quickly magnetization precesses (rotates) around the effective magnetic field. The paper suggests that for EuSe at low temperatures and high fields, this parameter is bounded by a value of 1.1 x 10^-3, which is consistent with a magnon lifetime of 2 nanoseconds.

Summary

The gist: The intrinsic ferromagnetic resonance (FMR) linewidth of an epitaxial EuSe film on a diamagnetic BaF2 substrate decreases upon cooling, becomes temperature independent at high frequencies up to 750 mK, and decreases with increasing frequency and field, suggesting low magnon damping in this material

Material Properties of EuSe

Europium chalcogenides are magnetic semiconductors whose moment of 7 µB per Eu2+ ion stems from a half-filled 4f shell with zero orbital momentum, so that spin-orbit coupling and intrinsic damping are expected to be weak The family spans the ferromagnets EuO and EuS, the metamagnet EuSe and the antiferromagnet EuTe In EuSe, the ferromagnetic nearest-neighbor exchange J1 and the antiferromagnetic next-nearest-neighbor exchange J2 nearly cancel, so that several stacking orders of the ferromagnetic (111) sheets are almost degenerate Its saturation magnetization of up to 1100 kA/m is more than five times that of YIG at low temperatures Below the N´eel temperature TN ≈ 4.6 K, the spins order antiferromagnetically (AFM I, AFM II), a small in-plane field stabilizes the ferrimagnetic ↑↑↓ phase, and a field of about 0.2 T aligns all spins In zero field below TN, EuSe thus carries no net moment and no stray field, which is attractive next to superconducting elements

Experimental Setup and Measurements

The research characterized an epitaxial film of the metamagnet EuSe on diamagnetic BaF2 by magnetometry and broadband ferromagnetic resonance from 10 K down to 30 mK The film was grown by molecular beam epitaxy on a BaF2(111) substrate, as described in Ref. 23 The static magnetization was measured by vibrating sample magnetometry (VSM) in a physical property measurement system (PPMS, Quantum Design) between 1.8 and 10 K with the field in the film plane, in up and down sweeps up to 2.5 T For FMR spectroscopy, a 3 mm wide piece of the film was placed face down on a coplanar waveguide The measurements were performed in the PPMS at frequencies from 15 to 70 GHz, and from 30 mK to 1.8 K in a dilution refrigerator with a superconducting vector magnet at frequencies up to 67.7 GHz Each FMR trace was fitted with a complex Lorentzian on a complex linear background, which yields the resonance field Bres and the loaded full linewidth at half maximum (FWHM) ∆BL The intrinsic linewidth is obtained from the depth D of the symmetrized transmission dip, in dB, as ∆B = ∆BL 10−D/20

Magnon Damping Analysis

The magnon damping of EuSe, a key parameter for its application in quantum magnonics, remains largely unexplored The intrinsic FMR linewidth decreases with increasing frequency and field, and below 750 mK it no longer depends on temperature At 30 mK, 68 GHz and 1.8 T, it reaches 5.5 mT, which corresponds to a magnon lifetime of 2 ns and to an upper bound of 1.1 × 10−3 for the Gilbert damping parameter This behavior is consistent with a magnon lifetime of 2 ns The linewidth below TN decreases with increasing frequency and approaches a constant value above about 45 GHz

Comparison with Other Materials

In contrast to a Gilbert-damped ferromagnet, the linewidth of the field-aligned film decreases with increasing frequency and field The diamagnetic substrate eliminates this stray-field mechanism, which for YIG required the design of a novel and complex diamagnetic substrate EuSe on BaF2 shows no damping increase down to 30 mK The residual linewidth at high fields, which depends neither on temperature nor on frequency, is consistent with an inhomogeneous distribution of local resonance fields Compared with Permalloy at 10 K, EuSe is broader below 30 GHz but four times narrower at 66 GHz, and near 70 GHz its linewidth is still about 15 times larger than that of YIG films on diamagnetic garnet substrates at low temperatures

Conclusion on Damping

The temperature independence up to 750 mK constrains the nature of the residual broadening, arguing against thermally populated magnons and temperature-dependent scattering processes as its dominant origin The remaining broadening is extrinsic, and the narrower lines of purified bulk crystals indicate that it can be reduced further by materials development The effective magnetization equals the full spin-only moment at high temperatures, where the resonance is that of paramagnons of the field-polarized paramagnetic phase This material makes EuSe a versatile platform for quantum magnonics and spintronics

How it works

The magnetic properties stem from a half-filled 4f shell with zero orbital momentum, leading to expected weak spin-orbit coupling and intrinsic damping.
The material exhibits multiple magnetic phases including antiferromagnetic, ferrimagnetic, and ferromagnetic states reached with fields below 0.25 T.
The FMR linewidth decreases with increasing frequency and field, which is a characteristic of the film's behavior compared to Gilbert-damped ferromagnets.
The lack of damping increase down to 30 mK on the BaF2 substrate rules out the mechanism that dominates low-temperature damping in YIG films on paramagnetic GGG.
The intrinsic linewidth approaches a constant value above about 45 GHz, consistent with a magnon lifetime of 2 ns and an upper bound of 1.1 × 10−3 for the Gilbert damping parameter at high field and low temperature.

Key Findings

**- The FMR linewidth decreases upon cooling, is temperature independent at high frequencies up to 750 mK, and decreases with increasing frequency and field. This behavior is consistent with a magnon lifetime of 2 ns. **

**- The material provides a zero-field state without net moment and stray field while fields below 0.25 T switch it between AFM, FiM, and FM phases. **

**- The intrinsic linewidth is determined by the depth D of the symmetrized transmission dip, yielding an upper bound for the Gilbert damping parameter of 1.1×10−3. **

**- The observation that no significant strain is present in the film is suggested because both transition fields, BT and AFM to FiM transition field, follow the phase diagram within 10 mT **

**- The linewidth of the 500 nm film exceeds that of the 240 nm film in common frequency ranges by a factor of 1.1 to 1.9 at equal temperatures. **

**- The decrease with frequency is observed in two EuSe films of different thickness, indicating it is a property of EuSe films rather than a particular sample or measurement setup.

Improvements for AI systems

Bold header: Improved Material Characterization for Quantum Magnonics

The improved system can accurately predict magnon lifetimes by utilizing the intrinsic FWHM values derived from comparing 240 nm and 500 nm film data, as this comparison shows that the decrease of the linewidth with increasing frequency is thus observed in two EuSe films of different thickness.

Bold header: Enhanced Damping Parameter Estimation

The system can calculate an upper bound for the Gilbert damping parameter by using the measured linewidths at 68 GHz and 30 mK, which are reported as 5.5 mT, corresponding to a magnon lifetime of 2 ns.

Bold header: Suppression of Extrinsic Loss Mechanisms

The AI can identify and quantify the contribution of extrinsic broadening by recognizing that the residual linewidth at high fields, which depends neither on temperature nor on frequency, is consistent with an inhomogeneous distribution of local resonance fields, thereby confirming that the residual broadening is extrinsic.

Bold header: Phase Diagram Prediction for Hybrid Systems

The system can map magnetic phase transitions by analyzing the field and temperature dependence of the metamagnetic steps in EuSe, which allows for the design of materials where fields below 0.25 T switch it between antiferromagnetic, ferrimagnetic and ferromagnetic phases.

Bold header: Quantum Information Interface Design

The improved system can optimize designs for hybrid quantum systems by leveraging the property that EuSe provides a zero-field state without net moment and stray field, making it a candidate material for hybrid quantum systems and quantum magnonics.

Abstract

The rapid development of quantum magnonics over the past decade has created a demand for magnetic materials that keep their magnon losses low at millikelvin temperatures and add functionality beyond that of the established iron garnets and ferromagnetic metals. The europium chalcogenides are natural candidates - they are magnetic semiconductors whose moment of 7,μ B per Eu 2+ ion stems from a half-filled 4f shell with zero orbital momentum, so that spin-orbit coupling and intrinsic damping are expected to be weak. Here we characterize an epitaxial film of the metamagnet EuSe on diamagnetic BaF 2 by magnetometry and broadband ferromagnetic resonance from 10 K down to 30 mK. EuSe combines a saturation magnetization of 1100 kA/m with antiferromagnetic, ferrimagnetic and ferromagnetic phases that are reached with fields below 0.25 T. In contrast to a Gilbert-damped ferromagnet, the linewidth of the field-aligned film decreases with increasing frequency and field, and below 750 mK it no longer depends on temperature. At 30 mK, 68 GHz and 1.8 T, it reaches 5.5 mT, close to the values of bulk single crystals, which corresponds to a magnon lifetime of 2 ns and to an upper bound of 1.1 times10-3 for the Gilbert damping parameter. These properties make EuSe and the europium chalcogenides promising materials for hybrid quantum systems and quantum magnonics.

Sources

Novel diamagnetic garnet-type substrate single crystals for ultralow-damping yttrium iron garnet Y3Fe5O12 films at cryogenic temperatures