FEM ferromagnet meshes¶

Scope and purpose¶

Choose a magnetic topology based on geometry, expected magnetization variation and backend support. Every page in this branch uses the same workflow: author object intent, apply it, build, inspect the realized mesh and perform an observable-based convergence study.

Scientific and numerical model¶

Selection guide¶

Parameters¶

Python API¶

Complete Python example

import fullmag as fm

nm = 1.0e-9
study = fm.study("free_tetrahedral_reference")
study.engine("fem")
study.device("cpu", precision="double")
study.mode("strict")
study.universe(
    mode="manual",
    size=(500 * nm, 300 * nm, 160 * nm),
    center=(0.0, 0.0, 0.0),
    padding=(0.0, 0.0, 0.0),
)
study.universe.mesh(
    minimum_element_size=20 * nm,
    maximum_element_size=80 * nm,
    maximum_element_growth_rate=1.5,
    grading="geometric",
)

magnet = study.geometry(
    fm.Ellipsoid(110 * nm, 50 * nm, 20 * nm, name="ellipsoid"),
    name="ellipsoid",
)
magnet.mesh(
    mesh_strategy="free_tetrahedral",
    minimum_element_size=4 * nm,
    maximum_element_size=8 * nm,
    maximum_element_growth_rate=1.35,
    algorithm_2d=6,
    algorithm_3d=1,
    order=1,
    smoothing_steps=3,
    optimize="Netgen",
    optimize_iterations=3,
    compute_quality=True,
    per_element_quality=True,
)
magnet.Ms = 800.0e3
magnet.Aex = 13.0e-12
magnet.alpha = 0.02
magnet.m = fm.texture.uniform(1.0, 0.0, 0.0)

study.exchange()
study.demag(realization="poisson_robin")
study.build_domain_mesh()
study.stages.add_relax(
    stage_id="equilibrium",
    algorithm="llg_overdamped",
    tolA=1.0e-4,
    max_steps=20_000,
)

Control Room workflow¶

1. In Explorer, select the magnetic object’s Mesh child (the object mesh-policy route).

2. In Inspector → Object Mesh Policy, enable Use object policy when an object-specific override is required.

3. Configure the relevant groups: Mesh Size Presets, Element Size Parameters, Thin-Film Sweep Strategy, Interface and Transition Refinement, Backend Mesh Parameters, Core Relaxation, Manual Size Field, and Edge and Corner Refinement.

4. Select Apply Object Policy. This stores authoring intent and invalidates mesh resources whose revision no longer matches the model.

5. Select Build Mesh. If the draft is dirty, the panel applies it first and dispatches the canonical mesh.build-selected command.

6. Open the Quality and History tabs. Compare requested and realized values, then inspect the scoped size/quality distributions and the raw build report before running a solver.

The read-only effective values come from backend resources. They must not be reconstructed from the current form fields because presets, capability gates and backend normalization can change the resolved configuration.

Verification, quality and provenance¶

After every build, inspect the realized resource rather than assuming that the authored request was applied. The production check is:

• geometry and mesh revisions match the current model;

• requested and realized discretization/topology/order are recorded;

• node, element and boundary-facet counts are nonzero for every required region;

• region and boundary markers cover the complete topology;

• inverted and degenerate element counts are zero;

• interface diagnostics report no orphan, coincident, nonmanifold or unmatched facets;

• local size distributions are consistent with the intended edge/interface/core grading;

• any fallback or degradation has an explicit reason and an actual method;

• a mesh-refinement sequence demonstrates convergence of the scientific observable.

MeshQualityReport exposes signed inverse condition number (SICN), gamma/radius quality, volume statistics and optional per-element arrays. The source constants gamma_min=0.08 and SICN p05=0.1 are implementation gates for named report paths; they are not universal physical acceptance thresholds for every element family or study.

Mesh-convergence protocol¶

A production result should include at least three discretizations. Refine only the parameter under study while holding geometry, material parameters, solver tolerances, initial state and output sampling fixed. Let \(Q_h\) denote the observable for characteristic size \(h\). Report

with a documented scale for observables that can cross zero. For dynamics, compare resonance frequency, linewidth and mode profile; for relaxation, compare total energy and texture; for demag, compare field/energy and verify that moving the outer boundary does not change the result beyond the chosen tolerance.

Diagnostics and failure semantics¶

A magnetic mesh can be valid geometrically yet unsupported by the selected interaction. Inspect the active-lane capability matrix for polynomial order and every realized cell family before execution.

Where this is implemented¶

Implementation map reviewed against commit 5db00ccf0113b9756fec2d46feb36ade762b12c2 on 2026-08-24.

References¶

• C. Geuzaine and J.-F. Remacle, “Gmsh: a three-dimensional finite element mesh generator with built-in pre- and post-processing facilities,” International Journal for Numerical Methods in Engineering 79 (2009), 1309–1331, doi:10.1002/nme.2579.

• C. Abert, “Micromagnetics and spintronics: models and numerical methods,” European Physical Journal B 92, 120 (2019), doi:10.1140/epjb/e2019-90599-6.

• Gmsh reference manual, mesh algorithms, size fields, extrusion and physical groups: gmsh.info/doc/texinfo.

Documentation tree¶

Source-code index¶

This is a navigation page and introduces no standalone implementation symbol. The exact source-code index is maintained by the selected terminal page.