ICSD and literature search for Fe₃CuAs₂ as a RE-free permanent magnet candidate
ICSD and literature search for Fe₃CuAs₂ as a RE-free permanent magnet candidate
Hey
Fe₃CuAs₂ has no experimental synthesis record — no ICSD entry, no published synthesis. It does exist as a theoretical (DFT-only) entry in the Materials Project as mp-1225133, flagged theoretical: true. So it's been through DFT relaxation, but nobody has actually made the material.
It's the only entry in the Fe-Cu-As chemical system on MP.
You already built two template CIFs on the platform (June 28 and June 30), both relaxed with properties calculated via Ouro routes. Those align well with the MP data.
The MP entry crystallizes in
Hey
Fe₃CuAs₂ has no experimental synthesis record — no ICSD entry, no published synthesis. It does exist as a theoretical (DFT-only) entry in the Materials Project as mp-1225133, flagged theoretical: true. So it's been through DFT relaxation, but nobody has actually made the material.
It's the only entry in the Fe-Cu-As chemical system on MP.
You already built two template CIFs on the platform (June 28 and June 30), both relaxed with properties calculated via Ouro routes. Those align well with the MP data.
The MP entry crystallizes in
The closest known relatives in the broader Cu₂Sb-type family:
CuMnAs (P4/nmm): collinear AFM, T_N ≈ 480–507 K. Extensively studied for antiferromagnetic spintronics (Wadley et al., Nature 2014). Tetragonal phase is metastable, stabilized by epitaxial growth on GaAs/GaP/Si or Cu excess.
Mn₂As (Cu₂Sb type): AFM. Recent 2025 work (Olejník et al.) on quench switching.
Fe₂As (C38 / Cu₂Sb type): AFM. Studied at UIUC (Wu et al., Phys. Rev. Applied 2021) for anisotropic magnetoresistance.
Mn₂Sb (Cu₂Sb type): ferrimagnetic — the exception in this family, with Mn on both metal sublattices coupling ferrimagnetically.
CuFeAs: A Czech thesis (Charles University) computed CuFeAs in the Cu₂Sb-type structure (a = 3.78 Å, c = 5.75 Å), but as a 1:1:1 composition, not 3:1:2.
The dominant pattern is clear: Cu₂Sb-type pnictides are overwhelmingly antiferromagnetic. Mn₂Sb is the main ferrimagnetic exception, and that's because it has magnetic Mn on both sublattices. Fe₂As itself is AFM.
Pulled via the Ouro MP search route:
Property | MP value |
|---|---|
Formula | Fe₃CuAs₂ |
Space group | P-4m2 (No. 115, tetragonal) |
Theoretical | Yes — computed only, no experimental entry |
Energy above hull | 0.188 eV/atom |
Formation energy | +0.057 eV/atom |
Band gap | 0 (metallic) |
Density | 7.91 g/cm³ |
Volume | 79.97 ų (6 sites) |
Property | Value | Assessment |
|---|---|---|
Tc (Curie temp) | 458 K | Above room temp — good, if it's actually FM |
Total moment | 6.04 μB / 6 atoms (≈1.0 μB/atom) | Moderate |
Ms | 0.70 MA/m | Low for a PM (Fe = 1.71, Nd₂Fe₁₄B = 1.28) |
MAE | 0.032 meV/atom | Very low — bad for a permanent magnet |
Easy axis | [001] (uniaxial) | Good symmetry for PM |
κ (magnetic hardness) | 0.79 | Semi-hard, below the κ > 1 hard magnet threshold |
E above hull | 0.174 eV/atom | Metastable — not thermodynamically stable |
MP's hull energy (0.188 eV/atom) is close to our platform's value (0.174 eV/atom). The small difference likely comes from different relaxation parameters or MP's more complete phase diagram. Both agree: this is metastable, not on the hull.
Three red flags worth being honest about:
1. The magnetic ground state is probably AFM, not FM. Every close analog in this structure family (CuMnAs, Mn₂As, Fe₂As) is antiferromagnetic. The Cu₂Sb-type structure places transition metals on two sublattices that tend to couple antiparallel. The DFT routes on Ouro predict a Curie temperature (458 K) and a nonzero net moment (6 μB), which means they assumed or found a ferromagnetic state. But without explicitly checking competing AFM configurations, that FM result may be a local minimum, not the true ground state. An anomalous result (FM in an AFM family) should be treated as a bug until proven otherwise. That said, the P-4m2 non-centrosymmetry is a wrinkle — it opens the door to Dzyaloshinskii-Moriya interactions and more complex magnetic orderings that the standard AFM/FM dichotomy might not capture.
2. The MAE is too low for a permanent magnet. At 0.032 meV/atom, this is roughly 40x smaller than Nd₂Fe₁₄B (≈1.3 meV/atom). The κ of 0.79 confirms it sits in the semi-hard gap, not the hard magnet regime. Even if the moment and Tc were better, the anisotropy doesn't support permanent magnet function.
3. Thermodynamic metastability and positive formation energy. At 0.174–0.188 eV/atom above the hull, this is not stable. More concerning, MP reports a positive formation energy (+0.057 eV/atom), meaning the compound is energetically uphill from the elements. Most synthesizable intermetallics have negative formation energies. This doesn't rule it out entirely (some useful magnets are metastable, like τ-MnAl), but it makes synthesis significantly more challenging.
If you want to pursue this further, the obvious next step is running a magnetic structure competition: FM vs. the two canonical AFM configurations for Cu₂Sb-type (AF1 Mn₂As-style and AF2 Fe₂As-style) to see what the actual ground state is. The Czech thesis I found explicitly computed 12 magnetic configurations for Cu₂Sb-type Cr₂As using exactly this approach, so the methodology is well-established. The P-4m2 space group may also warrant checking for non-collinear or spiral magnetic orderings.
Happy to set that up, or move on to other candidates.
The closest known relatives in the broader Cu₂Sb-type family:
CuMnAs (P4/nmm): collinear AFM, T_N ≈ 480–507 K. Extensively studied for antiferromagnetic spintronics (Wadley et al., Nature 2014). Tetragonal phase is metastable, stabilized by epitaxial growth on GaAs/GaP/Si or Cu excess.
Mn₂As (Cu₂Sb type): AFM. Recent 2025 work (Olejník et al.) on quench switching.
Fe₂As (C38 / Cu₂Sb type): AFM. Studied at UIUC (Wu et al., Phys. Rev. Applied 2021) for anisotropic magnetoresistance.
Mn₂Sb (Cu₂Sb type): ferrimagnetic — the exception in this family, with Mn on both metal sublattices coupling ferrimagnetically.
CuFeAs: A Czech thesis (Charles University) computed CuFeAs in the Cu₂Sb-type structure (a = 3.78 Å, c = 5.75 Å), but as a 1:1:1 composition, not 3:1:2.
The dominant pattern is clear: Cu₂Sb-type pnictides are overwhelmingly antiferromagnetic. Mn₂Sb is the main ferrimagnetic exception, and that's because it has magnetic Mn on both sublattices. Fe₂As itself is AFM.
Pulled via the Ouro MP search route:
Property | MP value |
|---|---|
Formula | Fe₃CuAs₂ |
Space group | P-4m2 (No. 115, tetragonal) |
Theoretical | Yes — computed only, no experimental entry |
Energy above hull | 0.188 eV/atom |
Formation energy | +0.057 eV/atom |
Band gap | 0 (metallic) |
Density | 7.91 g/cm³ |
Volume | 79.97 ų (6 sites) |
Property | Value | Assessment |
|---|---|---|
Tc (Curie temp) | 458 K | Above room temp — good, if it's actually FM |
Total moment | 6.04 μB / 6 atoms (≈1.0 μB/atom) | Moderate |
Ms | 0.70 MA/m | Low for a PM (Fe = 1.71, Nd₂Fe₁₄B = 1.28) |
MAE | 0.032 meV/atom | Very low — bad for a permanent magnet |
Easy axis | [001] (uniaxial) | Good symmetry for PM |
κ (magnetic hardness) | 0.79 | Semi-hard, below the κ > 1 hard magnet threshold |
E above hull | 0.174 eV/atom | Metastable — not thermodynamically stable |
MP's hull energy (0.188 eV/atom) is close to our platform's value (0.174 eV/atom). The small difference likely comes from different relaxation parameters or MP's more complete phase diagram. Both agree: this is metastable, not on the hull.
Three red flags worth being honest about:
1. The magnetic ground state is probably AFM, not FM. Every close analog in this structure family (CuMnAs, Mn₂As, Fe₂As) is antiferromagnetic. The Cu₂Sb-type structure places transition metals on two sublattices that tend to couple antiparallel. The DFT routes on Ouro predict a Curie temperature (458 K) and a nonzero net moment (6 μB), which means they assumed or found a ferromagnetic state. But without explicitly checking competing AFM configurations, that FM result may be a local minimum, not the true ground state. An anomalous result (FM in an AFM family) should be treated as a bug until proven otherwise. That said, the P-4m2 non-centrosymmetry is a wrinkle — it opens the door to Dzyaloshinskii-Moriya interactions and more complex magnetic orderings that the standard AFM/FM dichotomy might not capture.
2. The MAE is too low for a permanent magnet. At 0.032 meV/atom, this is roughly 40x smaller than Nd₂Fe₁₄B (≈1.3 meV/atom). The κ of 0.79 confirms it sits in the semi-hard gap, not the hard magnet regime. Even if the moment and Tc were better, the anisotropy doesn't support permanent magnet function.
3. Thermodynamic metastability and positive formation energy. At 0.174–0.188 eV/atom above the hull, this is not stable. More concerning, MP reports a positive formation energy (+0.057 eV/atom), meaning the compound is energetically uphill from the elements. Most synthesizable intermetallics have negative formation energies. This doesn't rule it out entirely (some useful magnets are metastable, like τ-MnAl), but it makes synthesis significantly more challenging.
If you want to pursue this further, the obvious next step is running a magnetic structure competition: FM vs. the two canonical AFM configurations for Cu₂Sb-type (AF1 Mn₂As-style and AF2 Fe₂As-style) to see what the actual ground state is. The Czech thesis I found explicitly computed 12 magnetic configurations for Cu₂Sb-type Cr₂As using exactly this approach, so the methodology is well-established. The P-4m2 space group may also warrant checking for non-collinear or spiral magnetic orderings.
Happy to set that up, or move on to other candidates.