2026
|
Ohanyan, V.; Richter, J.; Sekania, M.; Giambattista, L.; Andreanov, A.; Kollar, M. Flat bands in the J1-J2-J3 XXZ sawtooth chain Journal Article Phys. Rev. B 113, 214418 (2026). @article{ohanyanFlatBandsJ_1J_2J_32026,
title = {Flat bands in the J_{1}-J_{2}-J_{3} XXZ sawtooth chain},
author = {V. Ohanyan and J. Richter and M. Sekania and L. Giambattista and A. Andreanov and M. Kollar},
url = {https://link.aps.org/doi/10.1103/byv6-h2m2},
doi = {10.1103/byv6-h2m2},
year = {2026},
date = {2026-06-04},
urldate = {2026-06-01},
journal = {Phys. Rev. B},
volume = {113},
number = {21},
pages = {214418},
abstract = {We consider a generalization of the XXZ model on the sawtooth spin chain with Dzyaloshinskii-Moriya interactions in which all exchange constants (symmetric, antisymmetric, and axial anisotropy) are different for the three different bonds of each triangle. We derive and resolve algebraic constraints on the exchange constants ensuring the appearance of a flat band in the one-magnon spectrum. The properties of the corresponding flat magnon bands and localized magnon states are analyzed. We further construct the mapping of the flat-band conditions for the Dzyaloshinskii-Moriya constants onto the Katsura-Nagaosa-Balatsky parameters. Based on the mapping, the possibility of the electric-field-driven flat bands with the aid of the magnetoelectric coupling is examined.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We consider a generalization of the XXZ model on the sawtooth spin chain with Dzyaloshinskii-Moriya interactions in which all exchange constants (symmetric, antisymmetric, and axial anisotropy) are different for the three different bonds of each triangle. We derive and resolve algebraic constraints on the exchange constants ensuring the appearance of a flat band in the one-magnon spectrum. The properties of the corresponding flat magnon bands and localized magnon states are analyzed. We further construct the mapping of the flat-band conditions for the Dzyaloshinskii-Moriya constants onto the Katsura-Nagaosa-Balatsky parameters. Based on the mapping, the possibility of the electric-field-driven flat bands with the aid of the magnetoelectric coupling is examined. |  |
Schilberth, F.; Kondákor, M.; Ukolov, D.; Pawbake, A.; Vasin, K.; Ercem, O.; Prodan, L.; Tsurkan, V.; Tsirlin, A. A.; Faugeras, C.; Lemmens, P.; Penc, K.; Kézsmárki, I.; Bordács, S.; Deisenhofer, J. Optical phonons as a testing ground for spin group symmetries Journal Article npj Quantum Mater. 11, 26 (2026), datadoi: 10.5281/zenodo.16751739. @article{schilberthOpticalPhononsTesting2025,
title = {Optical phonons as a testing ground for spin group symmetries},
author = {F. Schilberth and M. Kondákor and D. Ukolov and A. Pawbake and K. Vasin and O. Ercem and L. Prodan and V. Tsurkan and A. A. Tsirlin and C. Faugeras and P. Lemmens and K. Penc and I. Kézsmárki and S. Bordács and J. Deisenhofer},
url = {https://doi.org/10.1038/s41535-026-00857-9},
doi = {0.1038/s41535-026-00857-9},
year = {2026},
date = {2026-02-17},
urldate = {2026-02-01},
journal = {npj Quantum Mater.},
volume = {11},
pages = {26},
abstract = {Lattice vibrations are highly sensitive to crystal symmetries and their changes across phase transitions. The latter can modify irreducible (co)representations and corresponding infrared and Raman selection rules of phonons. This concept is established for relativistic magnetic point groups, simultaneously transforming spatial and spin coordinates. However, in altermagnets described by non-relativistic spin groups with disjunct symmetry operations for both vector spaces, the phonon selection rules have remained unexplored. Here, we present a detailed study of the infrared- and Raman-active modes in the collinear antiferromagnet and altermagnet candidate Co2Mo3O8. Comparing to ab initio calculations accurately capturing the eigenfrequencies, we identify all expected phonon modes at room temperature and deduce their selection rules using both symmetry approaches. Importantly, we observe the change of selection rules upon antiferromagnetic ordering, agreeing with the relativistic symmetry approach, while the spin group formalism predicts no changes. Therefore, optical phonons sensing the symmetry of the magnetic order can reveal if relevant magnon-phonon coupling is compatible with the spin-group approach or not.},
note = {datadoi: 10.5281/zenodo.16751739},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Lattice vibrations are highly sensitive to crystal symmetries and their changes across phase transitions. The latter can modify irreducible (co)representations and corresponding infrared and Raman selection rules of phonons. This concept is established for relativistic magnetic point groups, simultaneously transforming spatial and spin coordinates. However, in altermagnets described by non-relativistic spin groups with disjunct symmetry operations for both vector spaces, the phonon selection rules have remained unexplored. Here, we present a detailed study of the infrared- and Raman-active modes in the collinear antiferromagnet and altermagnet candidate Co2Mo3O8. Comparing to ab initio calculations accurately capturing the eigenfrequencies, we identify all expected phonon modes at room temperature and deduce their selection rules using both symmetry approaches. Importantly, we observe the change of selection rules upon antiferromagnetic ordering, agreeing with the relativistic symmetry approach, while the spin group formalism predicts no changes. Therefore, optical phonons sensing the symmetry of the magnetic order can reveal if relevant magnon-phonon coupling is compatible with the spin-group approach or not. |  |
Ohanyan, V.; Amiraghyan, L.; Sekania, M.; Kollar, M. Electric-field driven flat bands in the distorted sawtooth chain via the Katsura–Nagaosa–Balatsky mechanism Journal Article Z. Naturforsch. A 81, 289 (2026). @article{ohanyanElectricfieldDrivenFlat2026,
title = {Electric-field driven flat bands in the distorted sawtooth chain via the Katsura–Nagaosa–Balatsky mechanism},
author = {V. Ohanyan and L. Amiraghyan and M. Sekania and M. Kollar},
url = {https://doi.org/10.1515/zna-2025-0381},
doi = {doi:10.1515/zna-2025-0381},
year = {2026},
date = {2026-02-10},
urldate = {2026-02-01},
journal = {Z. Naturforsch. A},
volume = {81},
number = {4},
pages = {289},
abstract = {We investigate flat magnonic bands in a generalized sawtooth-chain model in which three sets of exchange parameters (symmetric Heisenberg exchange, axial Ising anisotropy, and antisymmetric Dzyaloshinskii–Moriya (DM) exchange) are assigned independently to each side of the triangular plaquette. If the effective Dzyaloshinskii–Moriya (DM) interaction parameters are generated via the Katsura–Nagaosa–Balatsky (KNB) mechanism of magnetoelectricity, they become explicit functions of the electric-field magnitude and direction, as well as of the lattice geometry, which in the present case is characterized by two bond angles. We focus on the situation in which these two angles are unequal, corresponding to a distortion of the triangular plaquette. Several electric-field–induced flat-band scenarios in the distorted sawtooth chain are analyzed, and expressions are derived for the electric-field strength required to drive the one-magnon excitations into a flat-band regime when the field is aligned along the lattice bonds. The saturation field and its dependence on the distortion angle are also examined. Finally, we establish a mapping between the flat-band solutions for a general DM interaction and its specific KNB-induced form.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
We investigate flat magnonic bands in a generalized sawtooth-chain model in which three sets of exchange parameters (symmetric Heisenberg exchange, axial Ising anisotropy, and antisymmetric Dzyaloshinskii–Moriya (DM) exchange) are assigned independently to each side of the triangular plaquette. If the effective Dzyaloshinskii–Moriya (DM) interaction parameters are generated via the Katsura–Nagaosa–Balatsky (KNB) mechanism of magnetoelectricity, they become explicit functions of the electric-field magnitude and direction, as well as of the lattice geometry, which in the present case is characterized by two bond angles. We focus on the situation in which these two angles are unequal, corresponding to a distortion of the triangular plaquette. Several electric-field–induced flat-band scenarios in the distorted sawtooth chain are analyzed, and expressions are derived for the electric-field strength required to drive the one-magnon excitations into a flat-band regime when the field is aligned along the lattice bonds. The saturation field and its dependence on the distortion angle are also examined. Finally, we establish a mapping between the flat-band solutions for a general DM interaction and its specific KNB-induced form. | |
Jarc, G.; Tartaglia, G.; Gabriele, F.; Forte, F.; Guarino, A.; Montanaro, A.; Rigoni, E. M.; Khatiwada, N.; Lincetto, C.; Bartolini, G.; Mastropasqua, A.; Mathengattil, S. Y.; Malvestuto, M.; Waqee-Ur-Rehman, M.; Fittipaldi, R.; Deisenhofer, J.; Tsirlin, A. A.; Vecchione, A.; Cuoco, M.; Fausti, D. Raman signatures of a non-reciprocal magnetic phase transition in Ca2RuO4 Unpublished (2026), arXiv.2609.07565. @unpublished{jarc2026ramansignaturesnonreciprocalmagnetic,
title = {Raman signatures of a non-reciprocal magnetic phase transition in Ca_{2}RuO_{4}},
author = {G. Jarc and G. Tartaglia and F. Gabriele and F. Forte and A. Guarino and A. Montanaro and E. M. Rigoni and N. Khatiwada and C. Lincetto and G. Bartolini and A. Mastropasqua and S. Y. Mathengattil and M. Malvestuto and M. Waqee-Ur-Rehman and R. Fittipaldi and J. Deisenhofer and A. A. Tsirlin and A. Vecchione and M. Cuoco and D. Fausti},
url = {https://arxiv.org/abs/2609.07565},
doi = {10.48550/arXiv.2609.07565},
year = {2026},
date = {2026-09-07},
urldate = {2026-09-07},
abstract = {The magnetic behavior of Ca2RuO4 represents a unique puzzle due to the interplay of strong electronic correlations, magneto-elastic interactions, and large spin-orbit coupling. At low temperatures, an anomalous Mott insulating state emerges, characterized by a complex antiferromagnetic order with a collective amplitude excitation of the magnetic moment which has been discussed in analogy with the Higgs mode. We report here evidence of a magnetic first-order phase transition driven by an out-of-plane magnetic field along the crystallographic c-axis of Ca2RuO4. Raman measurements in magnetic field reveal the emergence of mode of magnetic origin and a concomitant modification of the coupling between a phonon and the Higgs amplitude mode. Both the Raman features are characterized by a non-reciprocal hysteresis in magnetic field. Surprisingly, the observed phase transition does not affect the Raman scattering from the in-plane magnons, indicating that the dipolar antiferromagnetic order is preserved. This is consistent with the onset of a new quadrupolar field-controlled state, whose fluctuations structure can trigger an hybridization between the lattice and the magnetic Higgs mode resulting in the observed Raman features.},
note = {arXiv.2609.07565},
keywords = {},
pubstate = {published},
tppubtype = {unpublished}
}
The magnetic behavior of Ca2RuO4 represents a unique puzzle due to the interplay of strong electronic correlations, magneto-elastic interactions, and large spin-orbit coupling. At low temperatures, an anomalous Mott insulating state emerges, characterized by a complex antiferromagnetic order with a collective amplitude excitation of the magnetic moment which has been discussed in analogy with the Higgs mode. We report here evidence of a magnetic first-order phase transition driven by an out-of-plane magnetic field along the crystallographic c-axis of Ca2RuO4. Raman measurements in magnetic field reveal the emergence of mode of magnetic origin and a concomitant modification of the coupling between a phonon and the Higgs amplitude mode. Both the Raman features are characterized by a non-reciprocal hysteresis in magnetic field. Surprisingly, the observed phase transition does not affect the Raman scattering from the in-plane magnons, indicating that the dipolar antiferromagnetic order is preserved. This is consistent with the onset of a new quadrupolar field-controlled state, whose fluctuations structure can trigger an hybridization between the lattice and the magnetic Higgs mode resulting in the observed Raman features. |  |
Schilberth, F.; Vasin, K.; Knauft, M.; Kondákor, M.; Vuckovic, M.; Herrmann, N.; Penc, K.; Minola, M.; Keimer, B.; Martinez, V. A.; Panda, K.; Sirenko, A. A.; Prodan, L.; Tsurkan, V.; Tsirlin, A. A.; Kézsmárki, I.; Deisenhofer, J. Magnetic circular dichroism of THz modes and selection rules of Raman-active optical phonons in the polar altermagnet candidate Mn2Mo3O8 Unpublished (2026), arXiv:2608.01062. @unpublished{schilberth_magnetic_2026,
title = {Magnetic circular dichroism of THz modes and selection rules of Raman-active optical phonons in the polar altermagnet candidate Mn_{2}Mo_{3}O_{8}},
author = {F. Schilberth and K. Vasin and M. Knauft and M. Kondákor and M. Vuckovic and N. Herrmann and K. Penc and M. Minola and B. Keimer and V. A. Martinez and K. Panda and A. A. Sirenko and L. Prodan and V. Tsurkan and A. A. Tsirlin and I. Kézsmárki and J. Deisenhofer},
url = {https://arxiv.org/abs/2608.01062},
doi = {10.48550/arXiv.2608.01062},
year = {2026},
date = {2026-08-02},
urldate = {2026-08-01},
note = {arXiv:2608.01062},
keywords = {},
pubstate = {published},
tppubtype = {unpublished}
}
| |
Leone, L.; Dutta, A.; Heyl, M.; Prati, E.; Torta, P. Solving classical and quantum spin glasses with deep boltzmann quantum states Unpublished (2026), arXiv.2605.15899. @unpublished{leone2026solvingclassicalquantumspin,
title = {Solving classical and quantum spin glasses with deep boltzmann quantum states},
author = {L. Leone and A. Dutta and M. Heyl and E. Prati and P. Torta},
url = {https://doi.org/10.48550/arXiv.2605.15899},
doi = {10.48550/arXiv.2605.15899},
year = {2026},
date = {2026-05-15},
urldate = {2026-05-15},
abstract = {Variational neural network models have achieved remarkable success in solving ground-state problems of quantum many-body systems. However, addressing classical and quantum spin glasses remains challenging, as disorder and energy frustration give rise to an exponentially large number of local energy minima separated by high-energy barriers, hindering the efficiency of conventional Metropolis-based Monte Carlo methods. To bridge this gap, we introduce Deep Boltzmann Quantum States, a class of neural quantum states inspired by deep Boltzmann machines that inherit efficient block Gibbs sampling. We also propose two key advances in the training algorithm. Firstly, we combine natural-gradient updates with state-of-the-art stochastic optimizers. Secondly, we gradually tune the hardness of the problem Hamiltonian by interpolating from an easy to a hard regime, without the need to closely approximate the instantaneous adiabatic state at intermediate times. We match the exact solution or the best available estimate for several instances of classical and quantum Ising spin-glass models with infinite-range interactions and hundreds of spins. We also solve instances of the NP-hard Job Shop Scheduling Problem exceeding the current limitations of quantum annealing hardware. To summarize, deep neural architectures with efficient global update rules and trained within an annealing-like scheme, provide a powerful framework for solving real-world hard combinatorial optimization and for investigating disordered quantum many-body systems.},
note = {arXiv.2605.15899},
keywords = {},
pubstate = {published},
tppubtype = {unpublished}
}
Variational neural network models have achieved remarkable success in solving ground-state problems of quantum many-body systems. However, addressing classical and quantum spin glasses remains challenging, as disorder and energy frustration give rise to an exponentially large number of local energy minima separated by high-energy barriers, hindering the efficiency of conventional Metropolis-based Monte Carlo methods. To bridge this gap, we introduce Deep Boltzmann Quantum States, a class of neural quantum states inspired by deep Boltzmann machines that inherit efficient block Gibbs sampling. We also propose two key advances in the training algorithm. Firstly, we combine natural-gradient updates with state-of-the-art stochastic optimizers. Secondly, we gradually tune the hardness of the problem Hamiltonian by interpolating from an easy to a hard regime, without the need to closely approximate the instantaneous adiabatic state at intermediate times. We match the exact solution or the best available estimate for several instances of classical and quantum Ising spin-glass models with infinite-range interactions and hundreds of spins. We also solve instances of the NP-hard Job Shop Scheduling Problem exceeding the current limitations of quantum annealing hardware. To summarize, deep neural architectures with efficient global update rules and trained within an annealing-like scheme, provide a powerful framework for solving real-world hard combinatorial optimization and for investigating disordered quantum many-body systems. | |
2024
|
Kamenskyi, D.; Vasin, K.; Prodan, L.; Kutko, K.; Khrustalyov, V.; Pavlov, S. G.; Hübers, H. -W. Terahertz Resonant Emission by Optically Excited Infrared-Active Shear Phonons in KY(MoO4)2 Journal Article Adv. Sci. 12, 2407028 (2024). @article{kamenskyi_terahertz_2024,
title = {Terahertz Resonant Emission by Optically Excited Infrared-Active Shear Phonons in KY(MoO_{4})_{2}},
author = {D. Kamenskyi and K. Vasin and L. Prodan and K. Kutko and V. Khrustalyov and S. G. Pavlov and H. -W. Hübers},
url = {https://advanced.onlinelibrary.wiley.com/doi/abs/10.1002/advs.202407028},
doi = {10.1002/advs.202407028},
year = {2024},
date = {2024-11-13},
urldate = {2024-11-01},
journal = {Adv. Sci.},
volume = {12},
number = {2},
pages = {2407028},
abstract = {Abstract The generation of monochromatic electromagnetic radiation in the terahertz (THz) frequency range has remained a challenging task for many decades. Here, the emission of monochromatic sub-THz radiation by optical phonons in the dielectric material KY(MoO4)2 is demonstrated. The layered crystal structure of KY(MoO4)2 causes infrared-active shear lattice vibrations to have energies below 3.7 meV, corresponding to frequencies lower than 900 GHz where solid-state-based monochromatic radiation sources are rare. Directly excited by a 5 ps long broadband THz pulse, infrared-active optical vibrations in KY(MoO4)2 re-emit narrowband sub-THz radiation as a time-varying dipole for tens of picoseconds, which is exceptionally long for oscillators with frequencies below 1 THz. Such a long coherent emission allows for the detection of more than 50 periods of radiation with frequencies of 568 and 860 GHz. The remarkably long decay time together with the chemical stability of the employed material suggests a variety of possible applications in THz technology.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Abstract The generation of monochromatic electromagnetic radiation in the terahertz (THz) frequency range has remained a challenging task for many decades. Here, the emission of monochromatic sub-THz radiation by optical phonons in the dielectric material KY(MoO4)2 is demonstrated. The layered crystal structure of KY(MoO4)2 causes infrared-active shear lattice vibrations to have energies below 3.7 meV, corresponding to frequencies lower than 900 GHz where solid-state-based monochromatic radiation sources are rare. Directly excited by a 5 ps long broadband THz pulse, infrared-active optical vibrations in KY(MoO4)2 re-emit narrowband sub-THz radiation as a time-varying dipole for tens of picoseconds, which is exceptionally long for oscillators with frequencies below 1 THz. Such a long coherent emission allows for the detection of more than 50 periods of radiation with frequencies of 568 and 860 GHz. The remarkably long decay time together with the chemical stability of the employed material suggests a variety of possible applications in THz technology. | |
Vasin, K. V.; Strinić, A.; Schilberth, F.; Reschke, S.; Prodan, L.; Tsurkan, V.; Nurmukhametov, A. R.; Eremin, M. V.; Kézsmárki, I.; Deisenhofer, J. Optical magnetoelectric effect in the polar honeycomb antiferromagnet Fe2Mo3O8 Journal Article Phys. Rev. B 110, 054401 (2024). @article{vasin_optical_2024,
title = {Optical magnetoelectric effect in the polar honeycomb antiferromagnet Fe_{2}Mo_{3}O_{8}},
author = {K. V. Vasin and A. Strinić and F. Schilberth and S. Reschke and L. Prodan and V. Tsurkan and A. R. Nurmukhametov and M. V. Eremin and I. Kézsmárki and J. Deisenhofer},
doi = {10.1103/PhysRevB.110.054401},
year = {2024},
date = {2024-08-01},
urldate = {2024-08-01},
journal = {Phys. Rev. B},
volume = {110},
number = {5},
pages = {054401},
abstract = {The lack of both time-reversal and spatial inversion symmetry in polar magnets is a prerequisite for the occurrence of optical magnetoelectric effects such as nonreciprocal directional dichroism, i.e., a difference in refractive index and absorption for two counter-propagating electromagnetic waves, which has the potential for the realization of optical diodes. In particular, antiferromagnetic materials with magnetic excitations in the THz range such as Fe2Mo3O8 are promising candidates for next-generation spintronic applications. In a combined experimental and theoretical effort we investigated the THz excitations of the polar honeycomb antiferromagnet Fe2Mo3O8 in external magnetic fields and their nonreciprocal directional dichroism, together with the temperature dependence of the electronic transitions in the mid- and near-infrared frequency range. Using an advanced single-ion approach for the Fe ions, we are able to describe optical excitations from the THz to the near-infrared frequency range quantitatively and model the observed nonreciprocal directional dichroism in the THz regime successfully.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
The lack of both time-reversal and spatial inversion symmetry in polar magnets is a prerequisite for the occurrence of optical magnetoelectric effects such as nonreciprocal directional dichroism, i.e., a difference in refractive index and absorption for two counter-propagating electromagnetic waves, which has the potential for the realization of optical diodes. In particular, antiferromagnetic materials with magnetic excitations in the THz range such as Fe2Mo3O8 are promising candidates for next-generation spintronic applications. In a combined experimental and theoretical effort we investigated the THz excitations of the polar honeycomb antiferromagnet Fe2Mo3O8 in external magnetic fields and their nonreciprocal directional dichroism, together with the temperature dependence of the electronic transitions in the mid- and near-infrared frequency range. Using an advanced single-ion approach for the Fe ions, we are able to describe optical excitations from the THz to the near-infrared frequency range quantitatively and model the observed nonreciprocal directional dichroism in the THz regime successfully. | |
2023
|
Ghara, S.; Barts, E.; Vasin, K. V.; Kamenskyi, D.; Prodan, L.; Tsurkan, V.; Kézsmárki, I.; Mostovoy, M.; Deisenhofer, J. Magnetization reversal through an antiferromagnetic state Journal Article Nat. Commun. 14, 5174 (2023). @article{ghara_magnetization_2023,
title = {Magnetization reversal through an antiferromagnetic state},
author = {S. Ghara and E. Barts and K. V. Vasin and D. Kamenskyi and L. Prodan and V. Tsurkan and I. Kézsmárki and M. Mostovoy and J. Deisenhofer},
doi = {10.1038/s41467-023-40722-y},
year = {2023},
date = {2023-08-01},
urldate = {2023-08-01},
journal = {Nat. Commun.},
volume = {14},
number = {1},
pages = {5174},
abstract = {Magnetization reversal in ferro- and ferrimagnets is a well-known archetype of non-equilibrium processes, where the volume fractions of the oppositely magnetized domains vary and perfectly compensate each other at the coercive magnetic field. Here, we report on a fundamentally new pathway for magnetization reversal that is mediated by an antiferromagnetic state. Consequently, an atomic-scale compensation of the magnetization is realized at the coercive field, instead of the mesoscopic or macroscopic domain cancellation in canonical reversal processes. We demonstrate this unusual magnetization reversal on the Zn-doped polar magnet Fe2Mo3O8. Hidden behind the conventional ferrimagnetic hysteresis loop, the surprising emergence of the antiferromagnetic phase at the coercive fields is disclosed by a sharp peak in the field-dependence of the electric polarization. In addition, at the magnetization reversal our THz spectroscopy studies reveal the reappearance of the magnon mode that is only present in the pristine antiferromagnetic state. According to our microscopic calculations, this unusual process is governed by the dominant intralayer coupling, strong easy-axis anisotropy and spin fluctuations, which result in a complex interplay between the ferrimagnetic and antiferromagnetic phases. Such antiferro-state-mediated reversal processes offer novel concepts for magnetization control, and may also emerge for other ferroic orders.},
keywords = {},
pubstate = {published},
tppubtype = {article}
}
Magnetization reversal in ferro- and ferrimagnets is a well-known archetype of non-equilibrium processes, where the volume fractions of the oppositely magnetized domains vary and perfectly compensate each other at the coercive magnetic field. Here, we report on a fundamentally new pathway for magnetization reversal that is mediated by an antiferromagnetic state. Consequently, an atomic-scale compensation of the magnetization is realized at the coercive field, instead of the mesoscopic or macroscopic domain cancellation in canonical reversal processes. We demonstrate this unusual magnetization reversal on the Zn-doped polar magnet Fe2Mo3O8. Hidden behind the conventional ferrimagnetic hysteresis loop, the surprising emergence of the antiferromagnetic phase at the coercive fields is disclosed by a sharp peak in the field-dependence of the electric polarization. In addition, at the magnetization reversal our THz spectroscopy studies reveal the reappearance of the magnon mode that is only present in the pristine antiferromagnetic state. According to our microscopic calculations, this unusual process is governed by the dominant intralayer coupling, strong easy-axis anisotropy and spin fluctuations, which result in a complex interplay between the ferrimagnetic and antiferromagnetic phases. Such antiferro-state-mediated reversal processes offer novel concepts for magnetization control, and may also emerge for other ferroic orders. |  |
