{
  "status": "unknown",
  "advantages": [],
  "limitations": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-17",
  "slug": "magnetic-anisotropy",
  "term": "Magnetic anisotropy",
  "aliases": [],
  "definition": "Magnetic anisotropy is the dependence of magnetic energy or response on the direction of magnetization.",
  "note": "Preferred directions can arise from crystal structure, grain shape or stress; magnetocrystalline anisotropy is only one contribution [irm-anisotropy]. Anisotropy energy density, usually expressed in J/m3, is not itself a switching field or coercivity.\n\nIn a simplified zero-field uniaxial-grain model, the reversal barrier is K_u times V, where V is grain volume; dividing by k_B T gives a dimensionless stability factor [evans-2012]. Perpendicular media need the appropriate easy-axis orientation as well as isolated grains. Experiments on FePt intermediate layers show that improving grain morphology need not improve perpendicular anisotropy [dong-2016].",
  "related": [
    "pmr",
    "hamr",
    "superparamagnetic-limit",
    "magnetic-thermal-stability-factor",
    "magnetic-recording-trilemma"
  ],
  "citations": [
    {
      "id": "irm-anisotropy",
      "title": "Moskowitz: Magnetic Anisotropy, Institute for Rock Magnetism (1991 guide)",
      "url": "https://cse.umn.edu/irm/3-magnetic-anisotropy",
      "accessed": "2026-10-17"
    },
    {
      "id": "evans-2012",
      "title": "Evans et al.: Thermally induced error: density limit for magnetic data storage (2012), doi:10.1063/1.3691196",
      "url": "https://arxiv.org/html/1111.0524v2",
      "accessed": "2026-10-17"
    },
    {
      "id": "dong-2016",
      "title": "Dong et al.: Columnar structured FePt films epitaxially grown on large lattice mismatched intermediate layer (2016), doi:10.1038/srep34637",
      "url": "https://www.nature.com/articles/srep34637",
      "accessed": "2026-10-17"
    }
  ],
  "provenance": [
    "IRM supplies general magnetic background; its rock-specific values are not HDD media parameters.",
    "Dong et al. report thin-film experiments, not a commercial-drive lifetime study."
  ]
}