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Inelastic X-ray scattering with meV energy resolution (IXS) is an ideal tool to measure collective excitations in solids and liquids. In non-resonant scattering condition, the cross-section is strongly dominated by lattice vibrations (phonons). However, it is possible to probe additional degrees of freedom such as magnetic fluctuations that are strongly coupled to the phonons. The IXS spectrum of the coupled system contains not only the phonon dispersion but also the so far undetected magnetic correlation function. Here we report the observation of strong magnon–phonon coupling in LiCrO2 that enables the measurement of magnetic correlations throughout the Brillouin zone via IXS. We find electromagnon excitations and electric dipole active two-magnon excitations in the magnetically ordered phase and heavily damped electromagnons in the paramagnetic phase of LiCrO2. We predict that several (frustrated) magnets with dominant direct exchange and non-collinear magnetism show surprisingly large IXS cross-section for magnons and multi-magnon processes.

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“…Similar minima were previously observed in several TLAs such as CuCrO 2 (refs 24, 25), α -CaCr 2 O 4 (ref. 26) and LuMnO 3 (ref. 27).…”

Section: Resultsmentioning

confidence: 99%

Electromagnon dispersion probed by inelastic X-ray scattering in LiCrO2

et al. 2016

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“…However, precise numerical calculations for the spin-1=2 TLHAF, which take into account nearest-neighbor interactions only [24][25][26], indicate that quantum fluctuations are not enough to suppress magnetic ordering and the actual ground state is a noncollinear long-range ordered spin structure. Experiments on various spin-S triangular-lattice antiferromagnets have overwhelmingly confirmed this picture [27][28][29][30], with a few noteworthy exceptions [31][32][33]. Several perturbations from the pure TLHAF have been proposed to enhance quantum fluctuations: next-nearest neighbor (NNN) interactions [34][35][36][37][38], ring-exchange terms [39,40], and anisotropic exchange [41][42][43][44], although it remains theoretically unclear if the latter mechanism alone can stabilize a QSL [45][46][47][48].…”

Section: Introductionmentioning

confidence: 96%

Hierarchy of Exchange Interactions in the Triangular-Lattice Spin Liquid YbMgGaO4

et al. 2018

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The spin-1=2 triangular lattice antiferromagnet YbMgGaO 4 has attracted attention recently as a quantum spin-liquid candidate with the possible presence of off-diagonal anisotropic exchange interactions induced by spin-orbit coupling. Whether a quantum spin liquid is stabilized or not depends on the interplay of various exchange interactions with chemical disorder that is inherent to the layered structure of the compound. We combine time-domain terahertz spectroscopy and inelastic neutron scattering measurements in the field-polarized state of YbMgGaO 4 to obtain better insight of its exchange interactions. Terahertz spectroscopy in this fashion functions as a high-field electron spin resonance and probes the spin-wave excitations at the Brillouin zone center, ideally complementing neutron scattering. A global spin-wave fit to all our spectroscopic data at fields over 4 T, informed by the analysis of the terahertz spectroscopy linewidths, yields constraints on the disorder-averaged g factors and exchange interactions. Our results paint YbMgGaO 4 as an easy-plane XXZ antiferromagnet with the combined and necessary presence of subleading next-nearest neighbor and weak anisotropic off-diagonal nearest-neighbor interactions. Moreover, the obtained g factors are substantially different from previous reports. This work establishes the hierarchy of exchange interactions in YbMgGaO 4 from high-field data alone and thus strongly constrains possible mechanisms responsible for the observed spin-liquid phenomenology.

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“…4D INS is applied quite frequently to inorganic magnetic compounds or metals, where mostly antiferromagnetic (AFM), extended systems are studied , . Impressively complete plots of the magnon dispersion branches in ordered systems can be recorded relatively quickly , , . The technique is also ideally suited for studying the magnetic correlations in frustrated, disordered systems, where features are typically broad both in energy E and Q space, and are thus difficult if not impossible to identify from measurements at few points or in a limited ( E , Q ) range , , , .…”

Section: Introductionmentioning

confidence: 99%

“…[4,[7][8][9][10][11][12] Impressively complete plots of the magnon dispersion branches in ordered systems can be recorded relatively quickly. [7,8,[13][14][15] The technique is also ideally suited for studying the magnetic correlations in frustrated, disordered systems, where features are typically broad both in energy E and Q space, and are thus difficult if not impossible to identify from measurements at few points or in a limited (E,Q) range. [10,11,16,17] Even localized modes, resembling excitations in spin clusters, such as antiferromagnetic fluctuations of hexagons in the cubic spinel ZnCr 2 O 4 were detected.…”

Section: Introductionmentioning

confidence: 99%

Inelastic Neutron Scattering Intensities of Ferromagnetic Cluster Spin Waves

Prša

Waldmann

2019

Eur J Inorg Chem

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Inelastic neutron scattering (INS) is the key method for studying magnetic spectra. For ferromagnetic molecular nanomagnets the ferromagnetic cluster spin wave theory (FCSWT) exactly describes the low‐energy excitations from the ferromagnetic ground state. We provide a procedure starting from these molecular spin wave modes and ending with the experimentally observable INS spectra. The formulas for powder and single‐crystal spectra of isotropic and anisotropic ferromagnetic molecules are given. The INS interference pattern can be written in terms of “basis functions” fixed by the molecular geometry. We argue that this decomposition explicates the INS data when the spin wave modes are known and, vice versa, suggests a method to directly determine the quantum wavefunctions of the spin wave excitations based on the INS interference pattern. The calculation of INS observables is exemplified on three molecules: the Mn7 disc, the Mn10 supertetrahedron, and the Mn6 single molecule magnet.

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Magnetic Soft Modes in the Distorted Triangular Antiferromagnetα−CaCr2O4

Cited by 30 publications

References 28 publications

Electromagnon dispersion probed by inelastic X-ray scattering in LiCrO2

Electromagnon dispersion probed by inelastic X-ray scattering in LiCrO2

Hierarchy of Exchange Interactions in the Triangular-Lattice Spin Liquid YbMgGaO4

Inelastic Neutron Scattering Intensities of Ferromagnetic Cluster Spin Waves

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