synthetic surface and spm specific features

docs/nodes/MFM Current Simulation.md

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+# MFM Current Simulation
+
+Computes the magnetic stray field from an infinite current-carrying strip and the resulting force on an MFM tip. Useful for simulating the MFM response to current-carrying traces and interconnects.
+
+## Inputs
+
+| Name | Type | Required | Description |
+|------|------|----------|-------------|
+| field | DATA_FIELD | Yes | Topography used for grid dimensions (x/y size and resolution) |
+
+## Outputs
+
+| Name | Type | Description |
+|------|------|-------------|
+| hx | DATA_FIELD | In-plane (x) magnetic field component (A/m) |
+| hz | DATA_FIELD | Out-of-plane (z) magnetic field component (A/m) |
+| force | DATA_FIELD | Vertical force on the MFM tip (N) |
+
+## Controls
+
+| Name | Type | Default | Description |
+|------|------|---------|-------------|
+| height | FLOAT | 100e-9 | Tip-sample separation in metres |
+| current | FLOAT | 1e-3 | Strip current in amperes |
+| width | FLOAT | 100e-9 | Width of the current-carrying strip in metres |
+| tip_magnetization | FLOAT | 1e5 | Effective tip magnetic moment per unit volume in A/m |
+
+## Notes
+
+- The current strip is infinite along y and centred at x = 0, so the field varies only in the x direction.
+- Uses the Biot-Savart law for an infinite conducting strip of finite width to compute Hx and Hz.
+- Hx is the in-plane field component; Hz is the out-of-plane component.
+- Force is calculated with the point-dipole approximation: Fz = mu_0 * m_tip * dHz/dz.
+- Useful for simulating MFM response to current-carrying traces/interconnects.
+- Equivalent to Gwyddion's mfm_current.c.