Magnetic-Field Control of Topological Electronic Response near Room Temperature in Correlated Kagome Magnets

Strongly correlated kagome magnets are promising candidates for achieving controllable topological devices owing to the rich interplay between inherent Dirac fermions and correlation-driven magnetism. Here we report tunable local magnetism and its intriguing control of topological electronic response near room temperature in the kagome magnet ${\mathrm{Fe}}_3{\mathrm{Sn}}_2$ using small angle neutron scattering, muon spin rotation, and magnetoresistivity measurement techniques. The average bulk spin direction and magnetic domain texture can be tuned effectively by small magnetic fields. Magnetoresistivity, in response, exhibits a measurable degree of anisotropic weak localization behavior, which allows the direct control of Dirac fermions with strong electron correlations. Our work points to a novel platform for manipulating emergent phenomena in strongly correlated topological materials relevant to future applications.

Figure 1

${\mathrm{Fe}}_3{\mathrm{Sn}}_2$ structure and representative SANS data. (a) Structure of ${\mathrm{Fe}}_3{\mathrm{Sn}}_2$. (b) Fe breathing kagome lattice with short and long Fe bond lengths (red and blue, 2.59 and 2.75 Å). $a$, $a^{\prime }$, $a^{\prime \prime }$ denote equivalent Fe-Fe bond directions and $\perp$ denotes direction perpendicular to $a$. (c) Instrument setup for our SANS measurements. The neutron intensity is proportional to the square of magnetic moment $M$ that is perpendicular to neutron kinetic momentum transfer $q$. (d)–(g) SANS scattering patterns in zero magnetic field. (f),(g) Formation of bulk local magnetism when increasing temperature above 100 K. (h)–(l) and (m)–(q) Scattering patterns with magnetic fields parallel and perpendicular to the Fe-Fe bond, respectively. (e),(i),(n) are corresponding fits of scattering patterns in (d),(h),(m) using the anisotropic Lattice Lorentzian model [21]. White arrows indicate the direction of Fe-Fe bond $a$.

Figure 2

Magnetic properties. (a) Temperature dependence of the internal magnetic field ($H_{\mathrm{int}}$) and $\mu \mathrm{SR}$ relaxation rate ($\lambda$), showing a phase transition around 100 K. (b) Neutron intensity for domain along $a$, $a^{\prime }$, $a^{\prime \prime }$ at $H_{\perp }=0$ and 0.125 T. (c) Spin direction (magnetic domain) distribution $n$ along $a$, $a^{\prime }$, $a^{\prime \prime }$. Inset shows the change of spin distribution $\mathrm{\Delta }n=n(H)-n(H=0)$ divided by $|\sin ({\varphi }_H-{\varphi }_M)|$, where ${\varphi }_H$ is the magnetic field direction and ${\varphi }_M$ is the angular direction of $a$, $a^{\prime }$, $a^{\prime \prime }$, respectively. $|\mathrm{\Delta }n/\sin ({\varphi }_H-{\varphi }_M)|$ for all spin configuration can be described by an effective three-domain ($J=1$) Brillouin function. (d) Parallel and perpendicular field dependences of magnetic correlation lengths (domain size). A rearrangement of spin correlation at the mesoscopic scale is observed in the case of $H_{\perp }$.

Figure 3

In-plane magnetoresistivity. (a), (b) Angular variation of in-plane magnetoresistivity at 200 K in different magnetic fields for S1 and S2, respectively. The current is fixed along the Fe-Fe bond a (0°) and the magnetic field rotates in the plane. The angle between field and current is shown as the polar axis. Magnitude of the butterfly-wing pattern shows the variation of resistivity from its average value $\mathrm{\Delta }\rho /{\rho }_{\mathrm{avg}}$, where $\mathrm{\Delta }\rho =\rho -{\rho }_{\mathrm{avg}}$. $\rho$ is resistivity at each angle and ${\rho }_{\mathrm{avg}}$ is the averaged resistivity for all field directions. Black arrows indicate $\mathrm{\Delta }\rho /{\rho }_{\mathrm{avg}}$ maximum at angle ${\varphi }_{\max }$. (c) Magnetic field dependence of ${\rho }_{\mathrm{avg}}$, where $\mathrm{\Delta }{\rho }_{\mathrm{avg}}={\rho }_{\mathrm{avg}}(H)-{\rho }_{\mathrm{avg}}(H=0)$. (d) Comparison between Fe moment and $\mathrm{\Delta }\rho /{\rho }_{\mathrm{avg}}$ maximum as a function of field strength. Inset is an illustration of device geometry.

Figure 4

Weak localization conductivity and Dirac band. (a) Magnetic field dependence of conductivity of all field directions (${\varphi }_H$ shown as the color bar) for S1 and S2, respectively. $\mathrm{\Delta }{\sigma }_{2D}={\sigma }_{2D}(H)-{\sigma }_{2D}(H=0)$, as explained in the text. Dashed lines present the upper (green) and lower (yellow) boundaries by Hikami-Larkin-Nagaoka equation [26, 27] for weak localization. (b) Phase coherence characteristic field $H_{\varphi }$ and magnetic domain distribution measured by SANS. (c) Prefactor $\alpha$. (d) Theoretical estimation of single-band $\alpha$ based on Dirac mass [27]. (e) Illustration of massive Dirac band structure with the pseudospin Dirac model [1, 28].