Room temperature intrinsic anomalous Hall effect in disordered half-metallic ferromagnetic quaternary Heusler alloy CoRuFeSi

TL;DR

This work shows that the quaternary Heusler alloy CoRuFeSi exhibits a robust, room-temperature intrinsic anomalous Hall effect governed by Berry curvature, even in the presence of significant Co--Ru antisite disorder. Combining arc-melt synthesis, structural and magnetic characterization, and first-principles calculations, the authors identify a nodal-line semimetal electronic structure in the ordered phase and demonstrate that disorder redistributes Berry curvature, reducing the AHC from the ordered value while preserving half-metallicity. The intrinsic AHE remains large (σxy ≈ 74–98 S/cm across 5 K–300 K), making CoRuFeSi a promising disorder-tolerant ferromagnet for spintronic and Hall-based devices. The study also provides a framework for understanding how disorder modulates topological transport in Heusler compounds via Berry-curvature engineering.

Abstract

Quaternary Heusler alloys offer a versatile platform for engineering magnetic and topological transport phenomena through chemical flexibility and tunable disorder. Here, we report a comprehensive experimental and theoretical investigation of the magnetic, magnetotransport, and anomalous Hall properties of the quaternary Heusler alloy CoRuFeSi. The compound crystallizes in the LiMgPdSn-type structure with significant Co--Ru antisite disorder and exhibits soft ferromagnetism with a saturation magnetization of $4.21~μ_{\mathrm{B}}/\mathrm{f.u.}$ at low temperature and a Curie temperature well above room temperature. Hall measurements reveal a robust anomalous Hall effect persisting up to 300~K, with an anomalous Hall conductivity of $\sim 74$~S/cm that is nearly temperature independent. Scaling analysis demonstrates that the anomalous Hall response is dominated by the intrinsic Berry-curvature mechanism. First-principles calculations identify CoRuFeSi as a topologically nontrivial nodal-line semimetal in its ordered phase. Incorporation of experimentally relevant Co--Ru antisite disorder redistributes the Berry curvature and quantitatively reproduces the experimentally observed anomalous Hall conductivity, while preserving half-metallicity. These results establish CoRuFeSi as a disorder-tolerant half-metallic ferromagnet with a sizable intrinsic anomalous Hall effect at room temperature, highlighting its potential for spintronic and Hall-based device applications.

Figures (9)

• Figure 1: Room temperature powder x-ray diffraction data of CoRuFeSi refined with Rietveld refinement. Vertical bars indicate the Bragg's reflection (pink), and the blue line indicates the difference between the observed data and the calculated data. The insets show a zoomed view near (111) and (200) superlattice reflection peaks for different kinds of orderings. (i) XRD pattern with Y-type ordering, (ii) XRD pattern with 50$\%$ swap between the Co and Ru atom, and (iii) XRD pattern with 50$\%$ swap between the Fe and Si atom. Refinement considering 50$\%$ disorder between octahedral site atoms Fe and Si in configuration (i). (b) Primitive unit cell corresponding to the fitted structure. (c) The bulk cubic Brillouin zone.
• Figure 2: Isothermal magnetization $M(H)$ of CoRuFeSi measured at 4 K, showing soft-ferromagnetic behavior.
• Figure 3: Temperature dependent longitudinal resistivity ($\rho_{xx}(T)$) with a schematic drawing of the technique of measurement used for Hall voltage ($V_H$ ) and longitudinal voltage ($V_{xx}$ ) measurements. $\rho_{xx}(T)$. Inset shows the variation of resistivity under magnetic fields of 0 T, 3 T, and 9 T.
• Figure 4: (a) and (b) Magnetoresistance (MR) vs H and Hall resistivity ($\rho_{xy}$) vs H at different temperatures, respectively. (c) Isothermal magnetization taken at 4, 50, 100 and 300 K for CoRuFeSi.
• Figure 5: (a) Temperature dependence of the ordinary Hall coefficient $R_0$ (inset shows the corresponding temperature variation of the carrier density). (b) Temperature dependence of the anomalous Hall resistivity $\rho_{xy}^{A}$. (c) log--log plot of $\rho_{xy}^{A}$ vs $\rho_{xx}$, where the red solid line represents a linear fit to the data. (d) Anomalous Hall conductivity (AHC) as a function of magnetic field for different temperatures. (e) Temperature dependence of the AHC $\sigma_{xy}$ and longitudinal conductivity ($\sigma_{xx}$), and (f) $\rho_{xy}^{A}$ vs $\rho_{xx}$ with fitting to Eq. (3), shown by the red dashed line.