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arxiv: 2605.00540 · v1 · submitted 2026-05-01 · ❄️ cond-mat.str-el

Incommensurate Magnetic Ordered Phase with Enhanced Low-Temperature Magnetic Specific Heat in SmAu₃Al₇

Ryuji Higashinaka , Takuma Iwami , Kohsuke Saitou , Takashi U. Ito , Chihiro Tabata , Koji Kaneko , Takashi Ohhara , Ryoji Kiyanagi
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Akiko Nakao Jumpei G. Nakamura Wataru Higemoto Akihiro Koda Shinsaku Kambe Yuji Aoki Tatsuma D. Matsuda
This is my paper

Pith reviewed 2026-05-09 18:41 UTC · model grok-4.3

classification ❄️ cond-mat.str-el
keywords SmAu3Al7incommensurate magnetic orderneutron scatteringmuon spin rotationlong-range ordermagnetic specific heatstrongly correlated electrons
0
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The pith

Muon spin rotation and neutron scattering establish that the magnetic order in SmAu3Al7 is a spatially homogeneous long-range incommensurate state unchanged below the 0.9 K transition.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper uses neutron scattering on single crystals to detect magnetic Bragg peaks with an incommensurate propagation vector below 2.8 K. Muon spin rotation measurements detect spontaneous internal fields whose spectral shape matches this incommensurate order and shows no anomalies at the lower transition of 0.9 K. These observations rule out earlier suggestions of a partially disordered state. A sympathetic reader would care because clarifying the homogeneous character of the order helps explain the enhanced low-temperature magnetic specific heat reported for this material.

Core claim

Neutron scattering and muon spin rotation measurements on single-crystal SmAu3Al7 reveal magnetically ordered states associated with successive transitions at TN = 2.8 K and T* = 0.9 K. Magnetic Bragg peaks appear below TN with an incommensurate propagation vector q = (0.30, 0, 1.33). μSR detects spontaneous internal fields below TN, and the spectral shape is consistent with the IC magnetic ordering. No anomalies are observed at T*, indicating that the magnetic structure remains essentially unchanged below and above T*. The magnetic order is revealed to be a spatially homogeneous long-range ordered state, rather than a partially disordered state proposed in earlier studies.

What carries the argument

The incommensurate propagation vector q = (0.30, 0, 1.33) from neutron scattering together with the μSR spectral shape that confirms a uniform distribution of spontaneous internal fields.

If this is right

  • The magnetic structure does not change across the T* = 0.9 K transition.
  • The enhanced low-temperature magnetic specific heat is connected to the incommensurate magnetic order rather than to partial disorder.
  • Earlier models proposing a partially disordered magnetic state below TN are inconsistent with the combined neutron and μSR data.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • The T* transition may involve a small change in ordered-moment size or orientation that lies below the resolution of the present μSR measurements.
  • Related rare-earth intermetallic compounds with similar lattice parameters could be checked for analogous incommensurate orders that produce enhanced specific heat without requiring disorder.
  • Higher-resolution neutron scattering or local-probe measurements below 0.9 K could test whether the specific-heat enhancement arises from soft modes associated with the incommensurate modulation.

Load-bearing premise

That the absence of anomalies in the μSR spectra at T* = 0.9 K and the consistency of the spectral shape with IC ordering together prove the magnetic structure is unchanged and spatially homogeneous throughout the sample.

What would settle it

Observation of additional Bragg peaks, a shift in the propagation vector, or the appearance of multiple distinct internal-field components in μSR below T* = 0.9 K would indicate a change in structure or the presence of disorder.

Figures

Figures reproduced from arXiv: 2605.00540 by Akihiro Koda, Akiko Nakao, Chihiro Tabata, Jumpei G. Nakamura, Kohsuke Saitou, Koji Kaneko, Ryoji Kiyanagi, Ryuji Higashinaka, Shinsaku Kambe, Takashi Ohhara, Takashi U. Ito, Takuma Iwami, Tatsuma D. Matsuda, Wataru Higemoto, Yuji Aoki.

Figure 1
Figure 1. Figure 1: (Color online) (a) Crystal structure of SmAu3Al7 in the hexagonal representation, drawn using the VESTA program.9) (b) and (c) Temperature dependence of the magnetic specific heat, Cmag/T, and magnetic susceptibilities, reproduced from Ref.6) view at source ↗
Figure 2
Figure 2. Figure 2: (Color online) (a) Neutron scattering intensity map of the reciprocal (h 0 l) plane of SmAu3Al7 at 0.3 K (phase II), extracted from diffraction data collected on SENJU. Reflections indicated by arrows and circles correspond to nuclear and magnetic Bragg reflections, respectively. The two concentric ring-like features correspond to the (1 1 1) and (2 0 0) Debye-Scherrer rings from the copper sample holder. … view at source ↗
Figure 3
Figure 3. Figure 3: One-dimensional cuts along (a) (1.7, 0, l) and (b) (h, 0, 0.66) through the magnetic Bragg peak near (1.7, 0, 0.66), measured in phase II (0.3 K). Solid line represents the results of Gaussian fit view at source ↗
Figure 4
Figure 4. Figure 4: (Color online) θ-2θ scans through the magnetic Bragg peaks at (a) (2, 0, 2) - q, (b) (2, 0, 2) + q, and (c) (2, 0, -4) + q measured in phases I and II. The ratio of integrated intensities, I1.2 K/I0.3 K, is approximately 0.6 for all magnetic reflections. 10/10 view at source ↗
Figure 5
Figure 5. Figure 5: (Color online) (a) ZF-µSR spectra of SmAu3Al7 measured at 5.1, 2.0, and 0.31 K. The solid curves represent the best fits using Eq. (1). (b) Temperature dependence of the high-field cutoff of the continuous distribution of local magnetic fields at the muon site, Bmax. The normalized Bmax values (right axis) are compared with the normalized square roots of the magnetic scattering intensities obtained from th… view at source ↗
Figure 1
Figure 1. Figure 1: 11/10 view at source ↗
Figure 2
Figure 2. Figure 2: 800 750 700 650 600 550 Intensity (count/(300 sec)) 0.4 0.5 0.6 0.7 0.8 0.9 l (r.l.u.) (1.7, 0, l) 800 750 700 650 600 550 500 1.5 1.6 1.7 1.8 1.9 h (r.l.u) (h, 0, 0.66) (a) (b) view at source ↗
Figure 3
Figure 3. Figure 3: 12/10 view at source ↗
Figure 4
Figure 4. Figure 4: 0.1 0.08 0.06 0.04 0.02 0 A - ABG 0 1 2 3 4 5 Time (µs) ZF-µSR 5.1 K 2.1 K 0.31 K 1 0 㲋Imag(T) Imag(0), B max(T) B max(0) 0 1 2 3 4 T (K) 15 10 5 0 Bmax (mT) T* TN 㲋Imag(T) / Imag(0)) Bmax(T). Bmax(T) / Bmax(0) (a) (b) view at source ↗
Figure 5
Figure 5. Figure 5: 13/10 view at source ↗
read the original abstract

Neutron scattering and muon spin rotation ($\mu$SR) measurements on single-crystal SmAu$_3$Al$_7$ reveal magnetically ordered states associated with successive transitions at $T_{\rm N}$ = 2.8 K and $T^*$ = 0.9 K. Magnetic Bragg peaks appear below $T_{\rm N}$ with an incommensurate (IC) propagation vector ${\bf q}$ = (0.30, 0, 1.33). $\mu$SR detects spontaneous internal fields below $T_{\rm N}$, and the spectral shape is consistent with the IC magnetic ordering. No anomalies are observed at $T^*$, indicating that the magnetic structure remains essentially unchanged below and above $T^*$. The magnetic order is revealed to be a spatially homogeneous long-range ordered state, rather than a partially disordered state proposed in earlier studies. The possible connection between the IC magnetic order and the enhanced low-temperature magnetic specific heat is discussed.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 1 minor

Summary. The manuscript reports neutron scattering and μSR measurements on single-crystal SmAu₃Al₇, revealing incommensurate magnetic Bragg peaks below T_N = 2.8 K with propagation vector q = (0.30, 0, 1.33). μSR detects spontaneous internal fields whose spectral shape is stated to be consistent with IC ordering, with no anomalies observed at T* = 0.9 K. This leads to the conclusion that the magnetic order is a spatially homogeneous long-range ordered state (rather than the partially disordered state proposed in earlier work), with discussion of a possible link to the enhanced low-temperature magnetic specific heat.

Significance. If substantiated, the result clarifies the ground state of this rare-earth intermetallic, resolving prior ambiguity between homogeneous IC order and partial disorder using complementary single-crystal probes. The absence of change across T* and consistency with IC lineshapes would support models linking the order to thermodynamic anomalies. Strengths include the use of single crystals and two standard techniques (neutron diffraction for coherence length, μSR for local fields) on the same samples.

major comments (2)
  1. [Abstract] Abstract: The central claim that the order is a 'spatially homogeneous long-range ordered state, rather than a partially disordered state' rests on the qualitative statement that the μSR 'spectral shape is consistent with the IC magnetic ordering' and the absence of anomalies at T*. This is load-bearing for the distinction from earlier studies, yet no quantitative lineshape fits (e.g., to the expected Bessel-function distribution for IC order), error bars, or explicit upper limits on any static paramagnetic or disordered volume fraction are provided.
  2. [μSR measurements] μSR results: The lack of discontinuity at T* = 0.9 K constrains only the dominant ordered component; without reported relaxation rates, asymmetry amplitudes, or volume-fraction analysis across the full temperature range, possible minority disordered subpopulations or weak additional channels at T* remain unexcluded.
minor comments (1)
  1. [Abstract] The abstract refers to 'enhanced low-temperature magnetic specific heat' and its possible connection to the IC order, but does not specify whether new specific-heat data are presented or if the discussion relies solely on literature values; a brief statement or reference in the abstract would improve clarity.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for the careful and constructive review of our manuscript. The comments highlight important aspects of the μSR analysis that can be clarified and strengthened. We address each point below and indicate the revisions we will make.

read point-by-point responses

  1. Referee: [Abstract] Abstract: The central claim that the order is a 'spatially homogeneous long-range ordered state, rather than a partially disordered state' rests on the qualitative statement that the μSR 'spectral shape is consistent with the IC magnetic ordering' and the absence of anomalies at T*. This is load-bearing for the distinction from earlier studies, yet no quantitative lineshape fits (e.g., to the expected Bessel-function distribution for IC order), error bars, or explicit upper limits on any static paramagnetic or disordered volume fraction are provided.

    Authors: We agree that the distinction from prior work on partial disorder benefits from more quantitative support. The neutron data establish long-range IC order via resolution-limited Bragg peaks at the reported q-vector. For μSR, the observed lineshape is consistent with the incommensurate modulation (as expected from the Bessel-function distribution for a single-q IC structure), and the full initial asymmetry is recovered in the ordered state with no residual paramagnetic component visible. While explicit multi-site Bessel fits are complicated by the crystal structure and multiple muon stopping sites, we will add an explicit upper bound (<5%) on any static disordered or paramagnetic volume fraction derived from the asymmetry amplitude, together with error bars on the fitted internal-field parameters. We will revise the abstract and expand the μSR discussion accordingly. revision: partial

  2. Referee: [μSR measurements] μSR results: The lack of discontinuity at T* = 0.9 K constrains only the dominant ordered component; without reported relaxation rates, asymmetry amplitudes, or volume-fraction analysis across the full temperature range, possible minority disordered subpopulations or weak additional channels at T* remain unexcluded.

    Authors: We accept that a fuller temperature-dependent analysis strengthens the claim. Our data show that both the internal-field distribution and the total asymmetry amplitude remain continuous across T*, with no additional relaxation channel or loss of asymmetry that would indicate a minority disordered phase. We will add a supplementary figure (or expanded panel) displaying the temperature dependence of the asymmetry amplitude, the mean internal field, and the relaxation rate from 0.3 K to 4 K. This will explicitly demonstrate that the ordered volume fraction is temperature-independent and accounts for the entire sample both above and below T*, with no detectable anomalies at 0.9 K. revision: yes

Circularity Check

0 steps flagged

No circularity: purely observational experimental report

full rationale

This is an experimental paper reporting neutron scattering and μSR data on SmAu₃Al₇. Magnetic Bragg peaks establish the incommensurate propagation vector q=(0.30,0,1.33) below TN=2.8 K, and μSR spectra show spontaneous fields whose shape is stated to be consistent with IC order, with no feature at T*=0.9 K. The claim of spatially homogeneous long-range order (versus prior partial-disorder proposals) follows directly from these observations and their comparison to external benchmarks; no derivations, model equations, fitted parameters renamed as predictions, or self-citation chains are present. The paper contains no load-bearing steps that reduce to their own inputs by construction.

Axiom & Free-Parameter Ledger

0 free parameters · 2 axioms · 0 invented entities

The central claims rest on standard interpretations of neutron Bragg peaks and μSR internal-field distributions in magnetic materials; no free parameters or new entities are introduced.

axioms (2)
  • domain assumption Neutron scattering detects magnetic Bragg peaks whose positions directly yield the magnetic propagation vector.
    Standard assumption in condensed-matter magnetism experiments.
  • domain assumption μSR spectra whose shape is consistent with an incommensurate modulation indicate a spatially homogeneous magnetic order.
    Common interpretation in μSR studies of ordered magnets.

pith-pipeline@v0.9.0 · 5550 in / 1393 out tokens · 29081 ms · 2026-05-09T18:41:06.940791+00:00 · methodology

discussion (0)

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Reference graph

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