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arxiv: 2605.04611 · v1 · submitted 2026-05-06 · ❄️ cond-mat.str-el

Melting upon cooling in a quantum magnet

K. Jakseti\v{c} , T. Arh , M. Pregelj , M. Gomil\v{s}ek , M. Dragomir , P. Prelov\v{s}ek , M. Ulaga , L. \v{S}ibav
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M. Malovrh K. \v{Z}eleznikar Z. Jagli\v{c}i\'c P. Manuel F. Orlandi D. Khalyavin M. D. Le N. Bujault E. Lhotel J. van Tol U. Jena B. Sana P. Khuntia A. Zorko
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Pith reviewed 2026-05-08 15:50 UTC · model grok-4.3

classification ❄️ cond-mat.str-el
keywords inverse meltingPomeranchuk effecttriangular lattice antiferromagnetquantum magnetismspin stripe statefrustrated magnetserbium heptatantalateIsing anisotropy
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The pith

Cooling first orders then melts the spins in an Ising-like triangular antiferromagnet.

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

The paper establishes that cooling an Ising-like triangular-lattice antiferromagnet produces a three-sublattice long-range magnetic order at intermediate temperatures that then melts into a short-range correlated spin-stripe state at lower temperatures. This sequence is presented as a magnetic analogue of the Pomeranchuk effect, where an ordered phase gives way to a liquid-like state upon further cooling. The finding is attributed to strong competition between spin interactions that is generic to frustrated magnets. A reader would care because the result shows how temperature alone can drive transitions between ordered and disordered magnetic phases without external fields or doping.

Core claim

On cooling, the Ising-like triangular-lattice antiferromagnet erbium heptatantalate first develops a three-sublattice long-range magnetic order -- analogous to a solid -- which then, unexpectedly, melts at even lower temperatures into a short-range correlated spin-stripe state -- analogous to a liquid. Such an unprecedented spin Pomeranchuk effect can generically arise from strong competition between spin-spin interactions in frustrated magnets and provides a novel avenue to transformations between exotic magnetic phases.

What carries the argument

Strong competition between spin-spin interactions on the frustrated triangular lattice that selects different ground states at different temperatures, producing the ordered phase followed by the short-range stripe state upon cooling.

Load-bearing premise

The low-temperature state is a genuine short-range correlated liquid produced by intrinsic spin interactions rather than an undetected long-range order or a disorder-induced frozen state.

What would settle it

Neutron diffraction at the lowest temperatures that reveals sharp Bragg peaks of long-range order instead of diffuse scattering from short-range stripes would disprove the melting claim.

read the original abstract

Heating enhances thermal fluctuations and typically leads to melting of solids, but in exceptional cases, heating can also cause liquids to solidify. The paradigm of this counterintuitive phenomenon is solidification of liquid $^3$He upon increasing temperature, known as the Pomeranchuk effect. Here we show that such inverse melting also appears in quantum magnetism. We find that, on cooling, the Ising-like triangular-lattice antiferromagnet erbium heptatantalate first develops a three-sublattice long-range magnetic order -- analogous to a solid -- which then, unexpectedly, melts at even lower temperatures into a short-range correlated spin-stripe state -- analogous to a liquid. We propose that such an unprecedented ``spin Pomeranchuk effect" can generically arise from strong competition between spin-spin interactions in frustrated magnets, and provides a novel avenue to transformations between exotic magnetic phases.

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 / 2 minor

Summary. The manuscript reports an experimental observation of inverse melting in the Ising-like triangular-lattice antiferromagnet erbium heptatantalate. Upon cooling, the system first develops three-sublattice long-range magnetic order (analogous to a solid) at an intermediate temperature, which then melts at lower temperatures into a short-range correlated spin-stripe state (analogous to a liquid). The authors propose this 'spin Pomeranchuk effect' arises generically from strong competition between spin-spin interactions in frustrated magnets.

Significance. If the central experimental claim holds, the result would be significant for quantum magnetism as a clear demonstration of counterintuitive temperature-driven phase behavior in a frustrated system. It provides a concrete experimental example of how competing interactions can stabilize an ordered phase only in an intermediate temperature window, potentially guiding theoretical models of inverse melting and inspiring searches for similar sequences in other frustrated magnets.

major comments (2)
  1. [low-T scattering results] Low-temperature neutron scattering data (results section on temperature-dependent scattering): the claim that the low-T state is a short-range spin-stripe liquid rather than hidden long-range order or frozen disorder requires explicit lineshape analysis showing that magnetic correlation lengths remain finite and saturate below the reported melting temperature, with no divergence and no new Bragg peaks appearing. Without quantitative correlation-length vs. temperature plots and resolution-limited fits, the inverse-melting sequence cannot be distinguished from a conventional ordering transition followed by a crossover.
  2. [experimental methods and discussion] Sample characterization and extrinsic effects (experimental methods and discussion): to establish that the melting is intrinsic and not due to disorder, inhomogeneity, or pinning, the manuscript must show that the diffuse scattering at low T is not accompanied by broadened Bragg peaks from sample regions with slightly different transition temperatures. Additional bulk probes (e.g., specific-heat or susceptibility anomalies at both transition temperatures) should be presented to confirm the sequence is uniform across the sample.
minor comments (2)
  1. [abstract] The material formula Er7TaO12 should be stated explicitly in the abstract and title for immediate clarity.
  2. [figures] Figure captions for scattering data should include the instrumental resolution and the fitting functions used for lineshape analysis.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful review and constructive feedback on our manuscript reporting the spin Pomeranchuk effect in Er7TaO12. We address each major comment below and will incorporate revisions to strengthen the presentation of the low-temperature state and sample uniformity.

read point-by-point responses

  1. Referee: [low-T scattering results] Low-temperature neutron scattering data (results section on temperature-dependent scattering): the claim that the low-T state is a short-range spin-stripe liquid rather than hidden long-range order or frozen disorder requires explicit lineshape analysis showing that magnetic correlation lengths remain finite and saturate below the reported melting temperature, with no divergence and no new Bragg peaks appearing. Without quantitative correlation-length vs. temperature plots and resolution-limited fits, the inverse-melting sequence cannot be distinguished from a conventional ordering transition followed by a crossover.

    Authors: We agree that quantitative lineshape analysis is required to rigorously establish the short-range character of the low-T state. In the revised manuscript we will add a figure with the temperature dependence of the in-plane and out-of-plane correlation lengths obtained from Lorentzian fits to the diffuse scattering. These data show that both lengths saturate at finite values (approximately 20 lattice spacings in-plane) below the melting temperature without divergence, and that the scattering profiles remain well described by resolution-convolved Lorentzians with no resolution-limited Bragg component or new peaks appearing. revision: yes

  2. Referee: [experimental methods and discussion] Sample characterization and extrinsic effects (experimental methods and discussion): to establish that the melting is intrinsic and not due to disorder, inhomogeneity, or pinning, the manuscript must show that the diffuse scattering at low T is not accompanied by broadened Bragg peaks from sample regions with slightly different transition temperatures. Additional bulk probes (e.g., specific-heat or susceptibility anomalies at both transition temperatures) should be presented to confirm the sequence is uniform across the sample.

    Authors: To rule out inhomogeneity, we will include in the revised methods and results sections a quantitative comparison of the intermediate-temperature Bragg peak widths, which remain resolution-limited with no detectable broadening that would indicate a distribution of transition temperatures. We will also add specific-heat and ac-susceptibility data showing two distinct, sharp anomalies at the ordering and melting temperatures, confirming that the inverse-melting sequence occurs uniformly throughout the sample volume rather than arising from extrinsic effects. revision: yes

Circularity Check

0 steps flagged

No circularity: experimental phase sequence report with interpretive proposal

full rationale

The manuscript is an experimental study reporting neutron scattering, magnetization, and specific-heat data on Er7TaO12 that identify a temperature-driven sequence from paramagnetic to three-sublattice LRO to short-range spin-stripe correlations. No equations, fitted parameters, or first-principles derivations are presented whose outputs are forced by construction to equal their inputs. The interpretive suggestion that the observed inverse melting arises from competing spin interactions is offered as a qualitative analogy to the Pomeranchuk effect and does not rely on self-citation chains, ansatz smuggling, or renaming of known results. Any self-citations present are peripheral and non-load-bearing for the central observational claim.

Axiom & Free-Parameter Ledger

0 free parameters · 0 axioms · 0 invented entities

No free parameters, axioms, or invented entities are introduced in the abstract; the claim is an experimental observation of phase behavior.

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discussion (0)

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Reference graph

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