---
title: 'CuMnAs: Antiferromagnetic Metal for Spintronics'
url: https://www.emergentmind.com/topics/antiferromagnetic-metal-cumnas
type: topic
---

# CuMnAs: Antiferromagnetic Metal for Spintronics

Antiferromagnetic metal CuMnAs is a class of Mn-based compounds that display robust antiferromagnetic order, high Néel temperature, and a tunable semimetallic to semiconducting electronic structure. Both bulk and epitaxial thin film forms of CuMnAs—including orthorhombic, tetragonal, and hexagonal polymorphs—have become reference materials in the development of antiferromagnetic spintronics. These compounds exhibit electrically and optically switchable order parameters via spin–orbit torques and magnetoelastic coupling, and possess a range of topological and nonlinear electronic responses.

## 1. Crystal Structure, Phase Stability, and Sample Preparation

CuMnAs exists in several crystallographically distinct structures. The stable orthorhombic phase (`Pnma`) is realized in bulk CuMnAs and CuMnP, while a metastable tetragonal phase (`P4/nmm`) can be stabilized via epitaxial growth on lattice-matched III–V substrates (e.g., GaAs, GaP) or on Si [1402.3624]. A recently identified hexagonal phase, Cu$_{0.82}$Mn$_{1.18}$As, broadens the structural landscape [1908.01758].

| Polymorph        | Space Group | Magnetic Structure        | Key Features      |
|------------------|------------|--------------------------|-------------------|
| Orthorhombic     | Pnma       | Collinear AFM (bc-plane) | Semimetal–semi.   |
| Tetragonal       | P4/nmm     | In-plane/L$_{Néel}$ AFM  | Spintronic active |
| Hexagonal        | P6$_3$/mmc | 120° Triangular AFM      | In-plane isotropy |

Phase-pure tetragonal CuMnAs is challenging to synthesize in bulk due to a strong tendency for phase separation and competition from the orthorhombic structure; an excess of Cu is often required to avoid orthorhombic contamination [2204.00966]. Thin films are conventionally grown using molecular beam epitaxy (MBE), but industry-compatible routes such as magnetron sputtering have also enabled high-quality, electrically switchable films [1903.12387].

## 2. Antiferromagnetic Order and Magnetic Transitions

Both orthorhombic and tetragonal CuMnAs are robust collinear antiferromagnets with high Néel temperatures, in contrast to the weak (T$_N$ ≈ 50 K) antiferromagnetic order of cubic semi-Heusler CuMnSb [1102.5373]. In the tetragonal phase, neutron diffraction and XMLD confirm in-plane staggered ordering of Mn moments transforming within the $\Gamma_{5}^{-}$ representation [1402.3624]. 

Energy differences between FM and AFM configurations—calculated via DFT as E$_{\mathrm{FM}}$ – E$_{\mathrm{AFM}}$ ≈ 109 meV/f.u. (tetragonal) and ≈ 241 meV/Mn-atom (orthorhombic)—predict $T_N$ well above room temperature [1102.5373, 1402.3624]. Monte Carlo simulations based on DLM-extracted exchange integrals yield T$_N$ ≈ 480–495 K, strongly corroborated by experiment [1707.08478, 1809.06239].

In both tetragonal and orthorhombic phases, the AFM transition is accompanied by magnetoelastic coupling: lattice parameters exhibit discontinuities at T$_N$ and at lower-temperature transitions to weak ferromagnetic or canted states, evidenced by both XRD and calorimetry [2204.00966, 1709.03394, 1806.08334]. Some compositions (Cu$_{1.18}$Mn$_{0.82}$As, CuMn$_{0.964}$As$_{1.036}$) show further transitions to weak ferromagnetism near room temperature.

## 3. Electronic Structure and Topological Properties

DFT calculations for orthorhombic CuMnAs indicate that it lies at the brink of a semimetal–semiconductor transition, exhibiting a small but finite density of states (DOS) at E$_F$ [1102.5373]. The carrier concentration is high and predominantly p-type, but mobility is anomalously low and effective masses are large (m* ≈ 1.5 of m$_e$), signifying “massive fermion” behavior rather than Dirac/Weyl-like dispersion [1709.03394].

Theoretical proposals for Dirac semimetallicity require preservation of specific symmetries (e.g., screw axis S$_{2z}$); in real crystals, symmetry breaking due to magnetic easy axis selection or canting gaps the Dirac points and generates a more conventional semimetallic state [1709.03394, 1806.08334]. Step-edge As deficiency in thin films leads to zigzag reconstructions, enhancing spin polarization and creating localized edge states with elevated magnetic moments—a critical factor for topological responses and surface magnetism [1907.13171]. 

In the orthorhombic phase, nodal lines and gapped Dirac points close to E$_F$ contribute strong (spin) Berry curvature, giving rise to a prominent, anisotropic spin Hall effect ($\sigma^{S,γ}_{\alpha\beta}$), while anomalous Hall conductivity is symmetry-forbidden in the ground state, but can be large under external magnetic fields [2104.13704].

## 4. Defects, Phase Separation, and Magnetotransport

Systematic ab initio calculations and XRD analysis identify low-energy Mn and Cu vacancies and antisite defects as the dominant defect types in tetragonal CuMnAs [1708.06916, 1809.06239]. Their presence substantially affects resistivity, with Mn$_{\text{Cu}}$ antisites producing particularly pronounced virtual bound states at E$_F$. Experimentally observed room-temperature and low-temperature resistivities (≈160 µΩ·cm and 90 µΩ·cm, respectively) are in good agreement with defect-informed modeling [1809.06239].

High-resolution diffraction reveals nanoscale phase separation—coherent stripe-like domains with compositionally- and magnetically-distinct regions—arising via (pseudo-)spinodal decomposition, especially in non-stoichiometric and Cu-rich samples [2204.00966]. This phase separation modifies both exchange interactions and local anisotropy, resulting in inhomogeneous transport and magnetic behavior.

## 5. Electrical, Optical, and Thermal Control of the Néel Vector

CuMnAs thin films enable current-induced reorientation of the Néel vector via the intrinsic Néel-order spin–orbit torque (NSOT), arising due to the inversion-partner symmetry of the Mn sublattices [1607.08478, 1903.12387]. The action of NSOT is to generate local effective fields on the sublattices ($\mathbf{H}^{(A)}_{\text{eff}} = +\chi J$, $\mathbf{H}^{(B)}_{\text{eff}} = -\chi J$), which rotate the Néel vector ($\mathbf{L}$) perpendicular to the applied current. 

Switching is clearly detected through anisotropic magnetoresistance (AMR) and planar Hall effects. Thermal activation governs both the domain reorientation and relaxation: the energy barrier for switching (E$_B = K_{4\parallel} V_g$) is surmounted via a combination of NSOT and local Joule heating [1903.12387, 2106.05000]. Both orthogonal and polarity-driven current pulse schemes effect switching with distinct retention, reproducibility, and signal-to-noise properties [2106.05000].

Terahertz-pulse-induced ultrafast switching can be optically gated via transient photoconductivity in the substrate, allowing for spatially-localized suppression of magnetic reorientation with femtosecond precision and ~100 nm resolution [2106.08828]. Magneto-Seebeck microscopy (MSE) further extends the read-out toolkit, providing table-top imaging of 90°/180° domain wall motion [2004.05460].

## 6. Magnetic Domain Engineering, Anisotropy, and Device Integration

Patterning and strain engineering are effective levers for domain engineering in CuMnAs thin films [2302.09550]. Lithographically-defined edges impose surface anisotropy, while magnetoelastic coupling (destressing energy due to strain incompatibility) propagates the edge effect microns into the film. The effective domain wall width varies exponentially with distance from the patterned edge:
$$
\frac{1}{d_\mathrm{DW}^2} = \frac{1}{D^2} (1 - a\, e^{-x/el} )
$$
This interplay is captured by a combined model for exchange, magnetocrystalline, edge, and destressing energies. Compared to Mn$_2$Au, which has a much higher bulk anisotropy, CuMnAs shows pronounced susceptibility to shape and strain effects.

Such elastic and anisotropic phenomena are vital considerations when designing antiferromagnetic memory and logic elements, especially given the critical role of equilibrium domain configuration in setting switching characteristics and device reproducibility.

## 7. Nonlinear Hall Effect, Topological Phenomena, and Quench Switching

The intrinsic nonlinear Hall effect (INHE) in tetragonal CuMnAs serves as a direct, relaxation time–independent probe of the Néel vector. The key second order conductivity tensor is [2106.12695]:
$$
\sigma^{(\alpha\beta\gamma)}_{\rm INH} = 2e^3 \sum_{n \neq m} \mathrm{Re} \int \frac{d^3k}{(2\pi)^3} \frac{v^\alpha_n {\cal A}^\beta_{nm}{\cal A}^\gamma_{mn}}{\epsilon_n - \epsilon_m} \frac{\partial f(\epsilon_n)}{\partial \epsilon_n} - (\alpha \leftrightarrow \beta)
$$
This INHE can reach mA/V$^2$ and depends sensitively on both chemical potential and temperature, peaking near band edge crossings described by a tilted massive Dirac model. The non-Drude, T-odd INHE component allows detection of 180° Néel vector flips in PT-symmetric antiferromagnets, directly enabling electrical readout in spintronic devices. Symmetry analysis identifies 53 magnetic point groups supporting INHE.

Quench switching—the creation of metastable, resistive high-domain-wall-density states by rapid heating/cooling above/below T$_N$—has been demonstrated in both CuMnAs and Mn$_2$As [2411.01930]. The relaxation follows a superposition of stretched exponentials with time constants obeying an Arrhenius law, $\tau = \tau_0 \exp(E_b / k_BT)$, with $E_b$ proportional to $T_N$. The multilevel, long-lived (hours-scale at room temperature in Mn$_2$As) resistivity states open routes toward neuromorphic and analog memory functionalities.

## References

- [1102.5373]: "CuMn-V compounds: a transition from semimetal low-temperature to semiconductor high-temperature antiferromagnets"
- [1402.3624]: "Tetragonal phase of epitaxial room-temperature antiferromagnet CuMnAs"
- [1607.08478]: "Imaging current-induced switching of antiferromagnetic domains in CuMnAs"
- [1709.03394]: "Massive fermions with low mobility in antiferromagnet orthorhombic CuMnAs single crystals"
- [1806.08334]: "Spin-flop phase transition in the orthorhombic antiferromagnetic topological semimetal Cu0.95MnAs"
- [1809.06239]: "Tetragonal CuMnAs alloy: role of defects"
- [1903.12387]: "Electrical Néel-order switching in magnetron-sputtered CuMnAs thin films"
- [1907.13171]: "Emerging edge states on the surface of the epitaxial semimetal CuMnAs thin film"
- [1908.01758]: "An in-plane hexagonal antiferromagnet in the Cu-Mn-As system, Cu$_{0.82}$Mn$_{1.18}$As"
- [1911.12381]: "Spin flop and crystalline anisotropic magnetoresistance in CuMnAs"
- [2004.05460]: "Magneto-Seebeck microscopy of domain switching in collinear antiferromagnet CuMnAs"
- [2104.13704]: "Spin and anomalous Hall effects emerging from topological degeneracy in Dirac fermion system CuMnAs"
- [2106.05000]: "Low-Energy Switching of Antiferromagnetic CuMnAs/ GaP Using sub-10 Nanosecond Current Pulses"
- [2106.08828]: "Optically gated terahertz-field-driven switching of antiferromagnetic CuMnAs"
- [2106.12695]: "Intrinsic nonlinear Hall effect in antiferromagnetic tetragonal CuMnAs"
- [2204.00966]: "High-resolution diffraction reveals magnetoelastic coupling and coherent phase separation in tetragonal CuMnAs"
- [2302.09550]: "Magnetic domain engineering in antiferromagnetic CuMnAs and Mn$_2$Au devices"
- [2411.01930]: "Quench switching of Mn2As"

Source: https://www.emergentmind.com/topics/antiferromagnetic-metal-cumnas