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Inelastic Neutron Scattering Study on Skyrmion host compound GaV4Se8
Magnetic skyrmions have been extensively studied as a promising candidate for spintronics devices. The Néel-type skyrmion lattice (SkL) was found to be stabilized in a wider magnetic field-temperature range in polar Dzyaloshinskii-Moriya (DM) helimagnet GaV4Se8 [1,2] after first discovered in isostructural GaV4S8 [3]. The magnetic field-temperature phase diagrams of these materials were reproduced by first principal calculation and speculated to be differentiated by magnetic anisotropy [4]. GaV4Se8 undergoes a Jahn-Teller-type structural transition from space group F-43m to R3m at Ts=41 K [1]. Below Tc=18 K, a cycloidal spin structure with modulation wavelength 19.4 nm is realized in zero field, while a triangular SkL with lattice constant 22.4 nm is emerged by critical field Hc = 0.1 T, followed by a saturated forced-ferromagnetic phase above Hsat = 0.4 T [2].
In this study, an inelastic neutron scattering experiment was performed on the GaV4Se8 powder at zero magnetic field using HRC spectrometer at J-PARC to identify the spin Hamiltonian. Spin wave excitation with the band energy of 8 meV was observed, as shown in Fig.1(a), and approximately reproduced by an isotropic Heisenberg spin Hamiltonian using linear spin-wave theory (LSWT) considering a V4 molecular form factor, as shown in Fig. 1(b). Compared to the isostructural GaV4S8, in GaV4Se8, the stronger isotropic interaction with negligible small single-ion anisotropy is in consistent with first principal calculation [4], indicating an enlarged SkL regime in temperature range. The high critical magnetic fields of both start and end of SkL phase are attributed to the small single-ion anisotropy and the strong DM interactions in GaV4Se8. This work was published in Journal of the Physical Society of Japan [5].
References:
[1] Y. Fujima et al., Phys. Rev. B 95, 180410 (2017).
[2] S. Bordács et al., Sci. Rep. 7, 7584 (2017).
[3] I. Kézsmárki et al., Nat. Mater. 14, 1116-1122 (2015).
[4] D. A. Kitchaev et al., Phys. Rev. B 101, 054409 (2020).
[5] Z. Liu, R. Ide, T. Arima, S. Itoh, S. Asai, and T. Masuda, J. Phys. Soc. Jpn. 93, 124707 (2024).
Fig.1 (a) INS powder spectrum with incident energy Ei=25 meV after background subtraction. (b) Simulation of convoluted powder spectrum using LSWT after fitting.
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