{
  "slug": "magnetic-coercivity",
  "term": "Magnetic coercivity",
  "aliases": [
    "Coercivity",
    "Saturation coercivity"
  ],
  "definition": "Magnetic coercivity is the reverse field strength at which a specified magnetic quantity reaches zero on a hysteresis curve traced from saturation.",
  "note": "State the zero-crossing quantity: flux density B, polarization J or magnetization M, with H_cB, H_cJ or H_cM respectively. Coercivity is a field strength in A/m [iec-coercivity-2019]. Since J = mu_0 M, J and M share a zero crossing; the B convention can differ because B = mu_0 H + J [kiel-magnetic-quantities].\n\nRemanence instead describes the magnetic state remaining at zero applied field. NIST's micromagnetic reference problem defines coercivity through a magnetization projection and changes reversal behavior by varying geometry even with zero magnetocrystalline anisotropy [nist-mumag-2]. A coercivity value is therefore not the anisotropy energy density or a thermal-retention barrier.\n\nTDK Headway describes HAMR optical heating as temporarily reducing media coercivity so a magnetic head can write [tdk-hamr-coercivity]. State temperature, field direction and measurement conditions when comparing values; a static hysteresis result alone does not determine recording errors during a heating pulse [evans-thermal-writability].",
  "status": "unknown",
  "advantages": [],
  "limitations": [
    "A hysteresis zero crossing does not establish a complete drive's retention time or failure rate.",
    "The cited IEC method has a bounded measurement range; it is not a universal HDD-material specification."
  ],
  "related": [
    "hamr",
    "magnetic-anisotropy",
    "magnetic-thermal-stability-factor",
    "exchange-coupled-composite-media"
  ],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "citations": [
    {
      "id": "iec-coercivity-2019",
      "title": "IEC 60404-7:2019, sections 3.1-3.2 and 4: coercivity definitions and saturation (official SIST preview)",
      "url": "https://preview.sist.si/sist-preview/66789/869971b7d22247b485e7de53a4b62102/SIST-EN-IEC-60404-7-2020.pdf",
      "accessed": "2026-11-06"
    },
    {
      "id": "nist-mumag-2",
      "title": "NIST muMAG Standard Problem 2: coercivity, remanence and geometry-dependent reversal",
      "url": "https://www.ctcms.nist.gov/mumag/std2/spec2.html",
      "accessed": "2026-11-06"
    },
    {
      "id": "tdk-hamr-coercivity",
      "title": "TDK Headway: Technologies, HAMR discussion of optical heating and media coercivity",
      "url": "https://www.headway.tdk.com/technologies.html",
      "accessed": "2026-11-06"
    },
    {
      "id": "kiel-magnetic-quantities",
      "title": "H. Foell, Kiel University: Magnetic Materials, section 4.1.4, relations between B, H, J and M",
      "url": "https://www.tf.uni-kiel.de/matwis/amat/elmat_en/kap_4/backbone/r4_1_4.html",
      "accessed": "2026-11-06"
    },
    {
      "id": "evans-thermal-writability",
      "title": "Evans et al.: Thermally induced error: density limit for magnetic data storage, APL 100, 102402 (2012), doi:10.1063/1.3691196, equations 1-2",
      "url": "https://arxiv.org/html/1111.0524v2",
      "accessed": "2026-11-06"
    }
  ],
  "updated": "2026-11-06",
  "provenance": [
    "Definition and units: IEC 60404-7:2019, sections 3.1-3.2 and 4, read in the official SIST preview; the full standard was not reviewed.",
    "NIST provides an idealized micromagnetic benchmark, not measured HDD media or a reproduction performed by Hesela.",
    "TDK is cited for the heating mechanism only, not its capacity forecasts or reliability claims.",
    "Evans et al. use an equilibrium model with aligned easy axes; its numerical density estimates are not measurements of commercial granular HAMR."
  ]
}