Notes from Charting Regions of Cobalt’s Chemical Space

Sharing some notes as I go through this paper:

This paper came up as I was researching whether to go after MAE or coercivity as a next prediction/screening model.

MAE was the answer as it's intrinsic to the material and upstream of coercivity anyways. This paper shows that it's fundamental to predicting coercivity, so it'll be good to have.

This paper makes their computed data available here (published September 6, 2024):
https://zenodo.org/records/13712318

I'm still looking into it but ideally we can clean it to get material structure (CIF) to MAE constants.

The paper

1. Goal: Find cobalt molecules that keep their magnetic “north” and “south” better than today’s best single-molecule magnets.

2. What they did

   • Built a big digital library of 15,000-plus virtual cobalt complexes.

   • Optimized each one with quantum chemistry to measure its magnetic “lock-in” strength (the axial anisotropy D).

3. Big discovery: You don’t need fragile two-coordinate cobalt.
   A simple rule works:

   Put two strong, straight-line (“axial”) ligands very close to cobalt and keep all other bonds weaker or farther away.
   This “pseudo-linear” setup lets the cobalt keep a big orbital moment → huge magnetic anisotropy.

4. Numbers that matter

   • Nearly 200 new designs beat |D| > 100 cm⁻¹, many in 4–5 coordination.

   • One record hit reached |D| ≈ 250 cm⁻¹—better than any cobalt magnet reported so far.

5. Why it matters

   • Chemists now have a clear design recipe that is easier to synthesize and more stable than ultra-low-coordination compounds.

   • All data are released as the COMPASS database, so anyone can train ML models or pick promising targets for the lab.

Bottom line: give cobalt a straight, two-bond “spine,” relax the side bonds, and you unlock record-size magnetic stickiness—opening new paths to strong molecular and bulk magnets.

Translating it to Fe

2. Why iron is trickier than cobalt

• Iron’s built-in “magnet locking” power (spin-orbit coupling) is only about one-third of cobalt’s.

• So we need to help iron by:

  1. Keeping the same two-bond line, and

  2. Adding things that boost the effect—heavier neighbor atoms, stretched lattices, or extra strain.

3. Simple design rules for iron magnets

1. Short north-south bonds: Put atoms like N, B, Sb, or Ni directly above and below each iron atom.

2. Loose east-west bonds: Make the side bonds longer or weaker so they don’t cancel the effect.

3. Heavy helpers: Surround iron with a few heavier atoms (Ni, Sb, W, Pt) to amplify the locking power.

4. Built-in stretch: Use crystal structures that are naturally longer in one direction (tetragonal) or apply strain during processing.

4. Real-world crystal families that already follow these rules

Bottom line:

Treat each iron atom like a tiny bar magnet: clamp it firmly from the top and bottom, leave its sides free, and give it a heavier buddy or a bit of stretch. Do that, and cheap, earth-abundant iron can inch closer to the performance of today’s rare-earth super-magnets.