Spontaneous Anomalous Hall Effect at Room Temperature in Antiferromagnetic Material NbMnAs

Abstract

Recent studies have shown that certain antiferromagnetic (AFM) materials with the same symmetry breaking as ferromagnets can generate sufficiently large ferromagnetic (FM) responses. Here, we report that the new AFM material NbMnAs exhibits a large anomalous Hall effect (AHE) at zero field and at room temperature, despite having only a small net magnetization. A polycrystalline sample of NbMnAs, likely close to stoichiometric composition, exhibited an AFM state with a small spontaneous magnetization of approximately $6 \times 10^{-3} μ_{\rm B}$/Mn and the AHE below $T_{\rm N}=354\,{\rm K}$. In contrast, single crystals of NbMnAs obtained by a flux method exhibited a deficiency at the As site, {which resulted} in a decrease in $T_{\rm N}$ and an increase in spontaneous magnetization. Although improvement of the single-crystal growth is still required, our study reveals that NbMnAs is a novel material capable of exhibiting significant FM responses derived from antiferromagnetism at room temperature.

Figures (3)

• Figure 1: (a) Orthorhombic crystal structure of NbMnP and NbMnAs. The Mn atoms form zigzag chains along the $b$-axis. (b) XRD patterns for NbMnP$_{1-x}$As$_{x}$. Each $x$ was determined by XRF measurements. The black line represents the simulated pattern for NbMnAs, which has the same space group as NbMnP. The symbols indicate impurity phases: $\star$: NbAs, +: NbP, -: Nb, and ?: an unknown phase. (c) Substitution dependence of the unit-cell volume. The continuous increase in volume with increasing As content was observed.
• Figure 2: (Color online) (a) Temperature dependence of the magnetization at 0.1T, (b) substitution dependence of $T_{\rm N}$ and (c) hysteresis loops for the polycrystalline samples. A small but distinct increase in magnetization appears below $T_{\rm N}$. For NbMnAs, a drop in magnetization is observed due to the superconductivity of the Nb impurity. The continuous increase in $T_{\rm N}$, as well as the unit-cell volume, suggests that the magnetically ordered states of NbMnP and NbMnAs are described by the same symmetry. (d) Temperature dependence of the magnetization at 0.1T and (e) hysteresis loops for the single crystals. A distribution of $T_{\rm N}$ was observed, ranging from 290340K. The spontaneous magnetization is about ten times larger than that of the polycrystalline sample, which is presumed to originate from As deficiency.
• Figure 3: (a) Temperature dependence of a proportion of the electrical resistance $R(T)$ in $R(300K)$ for the polycrystalline NbMnAs with $T_{\rm N}=354$ K. (b) Hysteresis loop of $\rho_\mathrm{H}$ for the polycrystalline NbMnAs. (c) Temperature dependence of $\rho$ for the polycrystalline and single-crystal NbMnAs. Red lines are guide to data points of polycrystals. (d) Hysteresis loop of $\rho_\mathrm{H}$ for the single-crystal NbMnAs. (e) Temperature dependence of $\rho_\mathrm{AHE}$ for the polycrystalline and single-crystal NbMnAs and single-crystal NbMnP.(f) Temperature dependence of $\sigma_\mathrm{AHE}$ for the single-crystal NbMnAs.