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The self-organized vacancy order in Pr$_9$Ge$_{16}$
Authors:
Jayashani S. T. Wickramasinghe,
Melissa G. Anderson,
Kelci Graville,
Gregory T. McCandless,
Zachary J. Morgan,
Brianna R. Billingsley,
Tai Kong,
Hyunsoo Kim,
Aleksandr V. Chernatynskiy,
Simon G. Mitchell,
Liang Wu,
Julia Y. Chan,
Feng Ye,
Halyna Hodovanets
Abstract:
In this work, we report the discovery of a new crystal structure on the Ge-rich side of the Pr-Ge binary phase diagram. Using a high-temperature flux technique, we grew single crystals of $Pr_9Ge_{16}$, which adopt a previously unreported orthorhombic $Fdd$2 structure type featuring ordered Ge vacancies. We present the anisotropic magnetic properties and identify the crystallographic $b$ axis perp…
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In this work, we report the discovery of a new crystal structure on the Ge-rich side of the Pr-Ge binary phase diagram. Using a high-temperature flux technique, we grew single crystals of $Pr_9Ge_{16}$, which adopt a previously unreported orthorhombic $Fdd$2 structure type featuring ordered Ge vacancies. We present the anisotropic magnetic properties and identify the crystallographic $b$ axis perpendicular to the crystal plane as the magnetic easy axis. Temperature-dependent resistivity measurements reveal metallic behavior with a distinct anomaly at $T_{\mathrm{C}}$ = 14.3 K. Hall resistivity data indicate that electron-like carriers dominate, with a carrier concentration on the order of $10^{27}~\mathrm{m}^{-3}$. The magnetic order is readily suppressed by a magnetic field of approximately 0.4 T applied along the easy $b$ axis.
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Submitted 7 August, 2026; v1 submitted 14 July, 2026;
originally announced July 2026.
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Experimental investigation of altermagnetic order in Cr-doped FeSb2
Authors:
A K M Ashiquzzaman Shawon,
Eoghan Downey,
Shane Smolenski,
Thomas J. Hicken,
Tatenda Kanyowa,
Amir Henderson,
Si Athena Chen,
Mingyu Xu,
Trisha Musall,
Rafael Lopes Sabainsk,
Zachary J. Morgan,
Wei Tian,
Yuan Zhu,
Weiwei Xie,
Elena Gati,
Lu Li,
Zurab Guguchia,
Huibo Cao,
Na Hyun Jo
Abstract:
Altermagnets are a class of materials with compensated magnetic moments, in which spin sublattices are related by specific rotational symmetries other than inversion or translation. This allows time-reversal symmetry to be broken without a net magnetization. Cr-doped FeSb2 has been theoretically proposed as a candidate d-wave altermagnetic system, yet its magnetic ground state has remained unresol…
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Altermagnets are a class of materials with compensated magnetic moments, in which spin sublattices are related by specific rotational symmetries other than inversion or translation. This allows time-reversal symmetry to be broken without a net magnetization. Cr-doped FeSb2 has been theoretically proposed as a candidate d-wave altermagnetic system, yet its magnetic ground state has remained unresolved. Here, we synthesize single crystals of Fe1-xCrxSb2 and investigate their electrical transport and magnetic properties, with a focus on Fe0.85Cr0.15Sb2. Magnetization measurements suggest spin-compensated ordering below ~3.5 K, where magnetic moments align along the crystallographic b-direction. Transport measurements reveal a crossover from large positive to negative magnetoresistance, while an anomalous Hall response emerges below 5 K, indicating time-reversal symmetry breaking. Muon spin relaxation measurements confirm that the magnetic ordering below 3.5 K is bulk in nature. The absence of coherent oscillations in zero-field μSR spectra and of magnetic Bragg intensity in single-crystal neutron diffraction establishes that the magnetically ordered state is short-range or disordered, rather than collinear altermagnetic order. These results demonstrate that Cr-doping alone breaks time-reversal symmetry without stabilizing long-range altermagnetic order in FeSb2.
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Submitted 7 July, 2026; v1 submitted 1 May, 2026;
originally announced May 2026.
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Uniaxial strain tuned magnetism of the altermagnet candidate h-FeS
Authors:
Weiliang Yao,
Feng Ye,
Zachary J. Morgan,
Douglas L. Abernathy,
Ruixian Liu,
Sijie Xu,
Yuxiang Gao,
Kevin Allen,
Yuan Fang,
Emilia Morosan,
Qimiao Si,
Pengcheng Dai
Abstract:
Altermagnets are collinear magnetic materials with 'alter'nating local crystalline environments, characterized by joint spin and crystalline symmetries that enable ferromagnetic-like transport properties but with vanishing net magnetization. Hexagonal FeS (h-FeS) is a recently identified altermagnet candidate that shows a spontaneous anomalous Hall effect (AHE) accompanied by a tiny net magnetizat…
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Altermagnets are collinear magnetic materials with 'alter'nating local crystalline environments, characterized by joint spin and crystalline symmetries that enable ferromagnetic-like transport properties but with vanishing net magnetization. Hexagonal FeS (h-FeS) is a recently identified altermagnet candidate that shows a spontaneous anomalous Hall effect (AHE) accompanied by a tiny net magnetization. Here, we show that both the spontaneous AHE and magnetization can be effectively suppressed by an in-plane compressive strain. Since neutron diffraction measurements show that the applied uniaxial strain only modifies the in-plane domain population but does not affect the in-plane magnetic structure, the major effect of the applied strain is to tune the small $c$-axis ferromagnetic moment. Our results demonstrate a strong correlation between the tiny net magnetization and the spontaneous AHE in h-FeS, and show that uniaxial strain provides an effective knob to tune both properties in this altermagnet candidate for spintronic applications.
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Submitted 16 February, 2026;
originally announced February 2026.
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Non-Altermagnetic Origin of Exchange Bias Behaviors in Incoherent RuO$_2$/Fe Bilayer Heterostructures
Authors:
Shelby S. Fields,
Joseph C. Prestigiacomo,
Cory D. Cress,
Nicholas G. Combs,
Olaf van 't Erve,
Patrick G. Callahan,
Keith E. Knipling,
Michelle E. Jamer,
Frank M. Abel,
Feng Ye,
Arianna Minelli,
Zachary J. Morgan,
Haile Ambaye,
Masaaki Matsuda,
Avishek Maity,
Valeria Lauter,
Steven P. Bennett
Abstract:
Initially identified as a promising altermagnetic (AM) candidate, rutile RuO$_2$ has since become embroiled in controversy due to contradictory findings of modeling and measurements of the magnetic properties of bulk crystals and thin films. For example, despite observations of a bulk non-magnetic state using density functional theory, neutron scattering, and muon spin resonance measurements, patt…
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Initially identified as a promising altermagnetic (AM) candidate, rutile RuO$_2$ has since become embroiled in controversy due to contradictory findings of modeling and measurements of the magnetic properties of bulk crystals and thin films. For example, despite observations of a bulk non-magnetic state using density functional theory, neutron scattering, and muon spin resonance measurements, patterned RuO$_2$ Hall bars and film heterostructures display magnetotransport signatures of magnetic ordering. Among the characteristics routinely cited as evidence for AM is the observation of exchange bias (EB) in an intimately contacted Fe-based ferromagnetic (FM) layer, which can arise due to interfacial coupling with a compensated antiferromagnet. Within this work, the origins of this EB coupling in Ru-capped RuO$_2$/Fe bilayers are investigated using polarized neutron diffraction, polarized neutron reflectometry, cross-sectional transmission electron microscopy, and super conducting quantum interference device measurements. These experiments reveal that the EB behavior is driven by the formation of an iron oxide interlayer containing Fe$_3$O$_4$ that undergoes a magnetic transition and pins interfacial moments within Fe at low temperature. These findings are confirmed by comparable measurements of Ni-based heterostructures, which do not display EB coupling, as well as magnetometry of additional Fe/Ru bilayers that display oxide-driven EB coupling despite the absence of the epitaxial RuO$_2$ layer. While these results do not directly refute the possibility of AM ordering in RuO$_2$ thin films, they reveal that EB, and related magnetotransport phenomena, cannot alone be considered evidence of this characteristic in the rutile structure due to interfacial chemical disorder.
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Submitted 26 September, 2025;
originally announced September 2025.
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Long-lived dynamics of the charge density wave in TiSe2 observed by time-resolved neutron diffraction
Authors:
K. Dharmasiri,
S. S. Philip,
D. Louca,
S. A. Chen,
M. D. Frontzek,
Z. J. Morgan,
C. Hua
Abstract:
We use time-resolved elastic neutron scattering combined with laser heating to probe the temporal evolution of periodic lattice distortions (PLD) due to the formation of a charge density wave (CDW) state in 1T-TiSe$_{2}$ under extreme non-equilibrium conditions. Below the transition temperature, the PLD is manifested as a 2x2x2 superlattice superimposed on the average Bragg structure. Following ra…
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We use time-resolved elastic neutron scattering combined with laser heating to probe the temporal evolution of periodic lattice distortions (PLD) due to the formation of a charge density wave (CDW) state in 1T-TiSe$_{2}$ under extreme non-equilibrium conditions. Below the transition temperature, the PLD is manifested as a 2x2x2 superlattice superimposed on the average Bragg structure. Following rapid energy deposition with the laser, kinetic bottlenecks lead to a separation of timescales between the superlattice and the underlying lattice response. The superlattice melts on a characteristic timescale of approximately 3 s, whereas the average lattice responds more slowly to heating. Upon removal of the heat source, the Bragg lattice recovers within approximately 11 s, while the superlattice re-establishes on nearly twice that timescale. These results reveal an asymmetric evolution of short- and long-range order under extreme non-equilibrium conditions, in which local PLD correlations are destroyed prior to, and recover more slowly than, the average lattice structure.
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Submitted 25 June, 2026; v1 submitted 18 September, 2025;
originally announced September 2025.
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Temporal and spatial separations between spin glass and short-range order
Authors:
Margarita G. Dronova,
Feng Ye,
Zachary J. Morgan,
Yishu Wang,
Yejun Feng
Abstract:
Broken-symmetry-induced order parameters account for many phenomena in condensed matter physics. For spin glasses, such a framework dictates its theoretical construction, whereas experiments have only established dynamical behaviors such as frequency dependent magnetic susceptibility and aging but not the thermodynamic phase. Experimental techniques have limitations when the spin glass is probed a…
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Broken-symmetry-induced order parameters account for many phenomena in condensed matter physics. For spin glasses, such a framework dictates its theoretical construction, whereas experiments have only established dynamical behaviors such as frequency dependent magnetic susceptibility and aging but not the thermodynamic phase. Experimental techniques have limitations when the spin glass is probed as an isolated state. To resolve this conundrum, we create an evolution from long-range order using a well-controlled tuning of the disorder on a spinel's sublattice. Cross-referencing a series of specimens at both long (milliseconds to seconds) and short (picosecond) time scales illustrates the relationship between spin glass and long- and short-range orders. The dynamics of short- and long-range order formations are not affected by disorder, as revealed by neutron magnetic diffuse scattering, however the ranges of these orderings are changed by the introduced disorder. Across all specimens, the inflection point of the correlation length's temperature dependence fully matches with the peak in heat capacity, while spin glass can freeze either below or well above this characteristic temperature of spin order formation. Our results identify an uncorrelated coexistence of the two and attribute components of the spin glass to individual spins at domain walls between spin clusters.
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Submitted 10 July, 2025;
originally announced July 2025.
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Emergent hidden order in ice: frustration and glassiness from slow hydrogen dynamics
Authors:
Tianran Chen,
D. Jonathan P. Morris,
Isaac C. Ownby,
Anjana Samarakoon,
Arnab Banerjee,
Feng Ye,
Douglas L. Abernathy,
Zachary J. Morgan,
Joseph Lanier,
Konrad Siemensmeyer,
Bastian Klemke,
D. Alan Tennant
Abstract:
Frustrated systems can host hidden order, in which weak interactions select correlated structure from a highly degenerate manifold. Water ice Ih is the canonical example of such a manifold, yet whether its hydrogen disorder conceals local structure beyond the Bernal-Fowler ice rules has remained controversial. Here, using high-resolution inelastic neutron scattering on single-crystal heavy ice, we…
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Frustrated systems can host hidden order, in which weak interactions select correlated structure from a highly degenerate manifold. Water ice Ih is the canonical example of such a manifold, yet whether its hydrogen disorder conceals local structure beyond the Bernal-Fowler ice rules has remained controversial. Here, using high-resolution inelastic neutron scattering on single-crystal heavy ice, we identify strongly anisotropic librational phonons dispersing uniaxially along the crystallographic c axis - a spectroscopic signature inaccessible to bulk-averaging probes. A physics-guided analysis reveals that these excitations encode a hidden partial order: correlated polar armchair chains driven by a shallow stereochemical bias that creates an imperfectly flat energy landscape. This bias promotes nanoscale polar domains, yet frustrated topology prevents their straightforward coarsening into the ice XI ground state, trapping the system in a rugged configurational landscape that, within the experimentally constrained model, retains finite residual entropy even in the limit of infinitely slow cooling. These findings show that ice Ih is not a simple disordered solid, but a frustrated, partially ordered hydrogen network with glass-like arrest on a crystalline lattice, providing a microscopic framework that reconciles thermodynamic theory with spectroscopic observations.
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Submitted 13 August, 2026; v1 submitted 18 March, 2025;
originally announced March 2025.