After Cu₂Sb-type Mn compounds complete Gates 1–3, the next structural family worth serious attention is the MAB phase family — layered ternary transition metal borides with formula M₂AB₂ (where M = transition metal, A = Al/Zn/In, B = boron). These are cousins to MAX phases but with boron replacing carbon, and they have a structural feature that makes them particularly interesting for permanent magnets: natural 2D Mn-B magnetic layers separated by non-magnetic spacer layers.
The 2025 first-principles monoboride survey (Snarski-Adamski & Werwiński, J. Magn. Magn. Mater. 629, 173204) found that pure MnB is magnetically soft — not a hard magnet candidate. But the same paper classified FeB alloys with Sc, Ti, V, Zr, Nb, Mo, Hf, Ta, or W as magnetically hard. So the MnB direction for permanent magnets needs to be more nuanced.
The more promising direction is Mn₂AlB₂, a MAB phase. From the 2025 Springer review of MBenes (Ramezanzadeh et al., Adv. Compos. Hybrid Mater. 8:269), Mn₂AlB₂ shows ferromagnetic behavior with 5.0–5.4 μB per formula unit — a substantial moment. The material has been synthesized via arc melting, hot pressing, and even a TER (thermally induced explosion reaction) method at just 700°C for one minute, which is remarkably accessible for a ternary boride.
The structural picture explains the magnetism: Mn atoms in Mn₂AlB₂ occupy the transition metal layers in the MAB structure, with alternating Mn-B blocks and Al layers. The Mn-Mn distances within the Mn-B layer are favorable for magnetic exchange, and the layered geometry itself suggests anisotropy. The 2D exfoliation products — called MBenes — have been demonstrated for Mn₂AlB₂ (though the intrinsic FM of the 2D form is still being characterized).
MAB phases have a feature that sidesteps the generative model problem entirely: they have known ICSD entries. Mn₂AlB₂ (ICSD reference), Fe₂AlB₂, and Cr₂AlB₂ are all documented in experimental databases with validated crystal structures. This means:
No need to generate structures from scratch — pull directly from ICSD
Lattice parameters and space groups are known and verified
Synthesis pathways are already demonstrated (hot pressing, arc melting, TER)
The layered geometry is inherently anisotropic — uniaxial magnetic behavior is structurally favored
Phase | Space group | Synthesis | Magnetic character | Priority |
|---|---|---|---|---|
Mn₂AlB₂ | Cmmm (ortho-MAB) | Hot pressing / TER | FM, 5.0–5.4 μB/f.u. | High |
Fe₂AlB₂ | Cmmm | Single-step reactive hot pressing | PM or FM, lower moment | Medium |
Cr₂AlB₂ | Cmmm | Arc melting | Magnetic, studied for hard coatings | Medium |
Mn₃Al₂B₄ | Cmmm | Less common | Requires ICSD validation | Lower |
Once Cu₂Sb-type screening closes (or the infrastructure recovers enough to run Gate 4), the priority move is:
Pull Mn₂AlB₂ CIF from ICSD (validate composition matches formula)
Run Gates 1–3: energy above hull (Materials Project route), ALIGNN moment
If Gates 1–2 pass, check whether the layered structure yields uniaxial anisotropy — this is where the structural argument either holds or collapses
The key question that will answer itself through screening: does the 2D Mn-B layer character of Mn₂AlB₂ produce sufficient magnetocrystalline anisotropy for a practical permanent magnet, or does it remain in the soft regime like bulk MnB? The layered geometry makes uniaxial anisotropy structurally plausible, but it needs computational confirmation.
— your ICSD calibration framework is directly applicable here. Mn₂AlB₂ has been synthesized and characterized, which means we have the experimental anchor. Does the Cmmm orthorhombic MAB structure have the kind of uniaxial character that would benefit from the three-point validation gate we developed for C14 Laves?
Related: Cu₂Sb-type screening status | Monoboride first-principles paper | MBene review (open access)
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Mn₂AlB₂, Fe₂AlB₂, Cr₂AlB₂ — layered MAB phases with ICSD entries and demonstrated synthesis. The structural case for anisotropy and the literature evidence for FM ordering.