Fe-Co-V-N-B-Cu permanent magnet design

Below is a “from‑scratch” permanent‑magnet concept that stitches together the best lessons from tetragonal Fe‑Co physics, rapid ordering tricks, and exchange‑spring nanocomposites. I kept every element earth‑abundant, readily recyclable, and friendly to mass‑production metallurgy.

1) Design goals

2) Chemistry & crystal structure

Hard nanograins (70 vol %)

Fe$_{0.55}$Co$_{0.30}$V$_{0.07}$N$_{0.03}$B$_{0.05}$ Body‑centred tetragonal Fe‑Co‑V‑N (c/a ≈ 1.22)

• V + N stabilise the bct lattice and lock in $K_u≈1–1.5 \text{MJ m}^{‑3}$ even in 100 nm films and bulk foils.

• Pure bct‑FeCo is predicted to rival or exceed FePt’s anisotropy while carrying 50 % more magnetisation.

Soft nanobridges (30 vol %)

Fe‑Co‑B (bcc) shells 3–5 nm thick around each hard grain

• Give an extra 0.4–0.5 T to $B_r$ through exchange‑spring coupling.

• B lowers grain‑boundary mobility, freezing grain size near 20 nm.

Pinning decorations

Cu/VC nano‑precipitates (<2 vol %) form during aging and immobilise domain walls.

3) Processing route (bench‑to‑kilogram scale)

1. Induction melt Fe‑Co‑V master alloy, over‑doped with 0.5 wt % B.

2. Gas‑atomise into ≤ 30 µm powder; high quench rate preserves metastable bct nuclei.

3. Reactive nitriding: NH$_3$ flow, 450 °C, 30 min → N uptake, full tetragonality.

4. Surfactant‑assisted ball mill 2 h → 15–25 nm crystallites.

5. Spark‑plasma sinter + 2 T field: 550 °C, 5 min → dense, c‑axes aligned bulk.

6. Age 400 °C, 1 h → Cu/VC precipitates and stress relief.

7. Passivate (phosphate dip or Al 99.5 % vacuum coating).

Every step is conventional powder‑metallurgy equipment; cycle time < 2 h.

4) Predicted magnetic performance

That slots the alloy squarely between MnAlC (≈8 MGOe) and today’s mid‑range Nd‑Fe‑B (35–45 MGOe)—without Dy, Nd or Sm.

5) Why each ingredient is there

6) Road‑map for validation

1. XRD (Cu Kα) to confirm c/a > 1.2 after nitriding.

2. TEM + EELS grain‑size and phase mapping.

3. VSM loops @ 300 K for $H_c$ & $B_r$.

4. Pulsed‑field testing to 10 T for irreversible field.

5. High‑T ageing (up to 200 °C for 1000 h) to benchmark thermal demagnetisation.

If loops match the table above, scale gas‑atomisation to 50 kg lots and feed existing powder‑bed fusion printers for net‑shape motor rotors.

7) CIF file design

data_HyperionX_bct
_symmetry_space_group_name_H-M    'I 4/mmm'
_symmetry_Int_Tables_number       139

# ----------------------------------------------------------------------
# Lattice parameters (metastable bct Fe‑Co‑V‑N‑B)
# ----------------------------------------------------------------------
_cell_length_a    2.850
_cell_length_b    2.850
_cell_length_c    3.480
_cell_angle_alpha 90
_cell_angle_beta  90
_cell_angle_gamma 90

# ----------------------------------------------------------------------
# Symmetry operations (standard for I4/mmm)
# ----------------------------------------------------------------------
loop_
  _symmetry_equiv_pos_as_xyz
  'x,  y,  z'
  '-x, -y,  z'
  '-y,  x,  z+1/2'
  ' y, -x,  z+1/2'
  'x,  y, -z'
  '-x, -y, -z'
  '-y,  x, -z+1/2'
  ' y, -x, -z+1/2'

# ----------------------------------------------------------------------
# Atom sites with mixed occupancies
# ----------------------------------------------------------------------
loop_
  _atom_site_label
  _atom_site_type_symbol
  _atom_site_fract_x
  _atom_site_fract_y
  _atom_site_fract_z
  _atom_site_occupancy

  Fe_M1   Fe  0.000  0.000  0.000  0.275   # 2a  site (mixed Fe/Co/V total occ = 1.0)
  Co_M1   Co  0.000  0.000  0.000  0.150
  V_M1    V   0.000  0.000  0.000  0.035

  Fe_M2   Fe  0.000  0.000  0.500  0.275   # 2b  site
  Co_M2   Co  0.000  0.000  0.500  0.150
  V_M2    V   0.000  0.000  0.500  0.035

  N_I1    N   0.000  0.500  0.250  0.030   # 4d interstitials (light elements)
  B_I1    B   0.000  0.500  0.250  0.050
  N_I2    N   0.500  0.000  0.250  0.030
  B_I2    B   0.500  0.000  0.250  0.050
  N_I3    N   0.000  0.500  0.750  0.030
  B_I3    B   0.000  0.500  0.750  0.050
  N_I4    N   0.500  0.000  0.750  0.030
  B_I4    B   0.500  0.000  0.750  0.050

TL;DR

A tetragonal Fe‑Co‑V‑N hard phase exchange‑coupled to Fe‑Co‑B soft shells should hit ~35 MGOe with nothing rarer than vanadium, survive 500 °C, and roll straight off a powder‑metallurgy line. That’s a permanent magnet worth chasing—and far more promising than cubic Fe$_{23}$(B,C)$_6$ or W‑doped variants.