Structural and magnetic phases of topological kagome metal Fe$_3$Sn$_2$ under pressure

Abstract

We investigate the pressure-induced evolution of crystal structure and magnetism in the kagome ferromagnet Fe$_3$Sn$_2$ by combining X-ray diffraction, X-ray Emission Spectroscopy, X-ray Magnetic Circular Dichroism, and spin-polarized density functional theory calculations. X-ray diffraction reveals a structural phase transition above $\sim$20~GPa, which coincides with a pronounced reduction of the local Fe magnetic moment evidenced by X-ray emission spectroscopy, indicating a high-spin to low-spin transition. While XES probes the amplitude of the local moment, XMCD provides direct information on the orientation of the ordered magnetic moments and uncovers a rich pressure--temperature magnetic phase diagram. At room temperature, a collinear ferromagnetic phase with moments aligned along the $c$ axis persists up to the structural transition. At low temperature, a tilted magnetic configuration remains stable to significantly higher pressures, while at intermediate temperatures pressure stabilizes the low-temperature magnetic phase at the expense of the high-temperature one. Spin-polarized first-principles calculations show that, although isotropic ferromagnetic exchange interactions remain robust under compression, pressure enhances spin--orbit--driven magnetic anisotropy and Dzyaloshinskii--Moriya interactions, favoring non-collinear magnetic configurations. Our results demonstrate that pressure reshapes the magnetic energy landscape of Fe$_3$Sn$_2$ by coupling lattice, spin state, and relativistic magnetic interactions, establishing hydrostatic pressure as an effective control parameter to engineer magnetic anisotropy and potentially topological phases in kagome materials.

Figures (7)

• Figure 1: (Color online) High-pressure X-ray diffraction analysis. (a) Color map showing the pressure evolution of X-ray diffraction patterns, revealing the emergence of additional peaks above 22 GPa, indicative of a structural phase transition. (b) Pressure dependence of the refined lattice parameters a (black symbols) and c (red symbols) obtained from Lebail refinement using the $R\bar{3}m$ space group up to the transition pressure. (c) Unit cell volume as a function of pressure (black squares) fitted with a third-order Birch–Murnaghan equation of state (solid black line). (d) Experimental high pressure (35.1 GPa) diffractogramm (black points) together with Le Bail fit (red line) using only the high pressure space group $Pnma$. The blue line is the difference between experimental data and fitted curve.
• Figure 2: (Color online) (a) Fe K$_\beta$ x-ray emission in $Fe_3Sn_2$ as a function of pressure measured at 300 K. The difference with 0 GPa is also plotted. (b) Evolution of the Integrated Amplitude Difference of the XES spectra as function of pressure (in black) compared to the evolution of the dichroic signal associated to ferromagnetism (in red).
• Figure 3: (Color online) (a-c) : X-ray absorption spectra and associated dichroic signal at Fe K-edge, performed at 1.3 T and 300, 30 and 100 K respectively. Dichroic signals are multiplied by a factor of 500 for a sake of visibility. The green area correspond to the intensity reported in panel (d). (d) Evolution of the ferromagnetic component along the $c$ axis deduced from the dichroic area (in green in (a-c)) and normalized to 2 $\mu_B$ at ambient condition (300 K and 0 GPa), for 30 K (blue), 100 K (green) and 300 K (red).
• Figure 4: Comparison between experimental and theoretical structural parameters of $Fe_3Sn_2$ under pressure. (a) Pressure dependence of the unit-cell volume. (b) Pressure dependence of the lattice parameters. Experimental data are compared with results obtained from density functional theory calculations, highlighting the agreement across the pressure-induced structural transition.
• Figure 5: Colour representation of dominant exchange interactions in the unit cell of Fe$_3$Sn$_2$.