@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 = {C4},

pubstate = {published},

tppubtype = {article}

}

@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 Fe2⁢Mo3⁢O8 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 Fe2⁢Mo3⁢O8 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 = {A1, C4},

pubstate = {published},

tppubtype = {article}

}

@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 = {A1, C4},

pubstate = {published},

tppubtype = {article}

}