{
  "aliases": [
    "Neel-Brown thermal activation model"
  ],
  "status": "research",
  "advantages": [],
  "limitations": [],
  "supersedes": [],
  "supersededBy": [],
  "firstSeen": null,
  "lastSeen": null,
  "updated": "2026-10-17",
  "slug": "neel-arrhenius-model",
  "term": "Neel-Arrhenius model",
  "definition": "The Neel-Arrhenius model describes thermally activated magnetic reversal with an exponential dependence on the ratio of an energy barrier to thermal energy.",
  "note": "With a state-to-state transition rate lambda = f_0 exp(-Delta), the mean dwell time is exp(Delta)/f_0. Rippard et al. use a field-dependent Neel-Brown dwell-time model for a measured two-state magnetic tunnel junction; zero effective field gives this simplified convention [rippard]. Attempt rates are model and device dependent.\n\nDo not silently identify a mean dwell time with an ensemble magnetization-decay time. In a symmetric two-state model with equal rates lambda, an initially aligned ensemble decays as exp(-2 lambda t), while first-reversal probability is 1-exp(-lambda t). These are distinct observables; the linked derivation and tests make the convention explicit [hesela-retention].",
  "related": [
    "magnetic-thermal-stability-factor",
    "superparamagnetic-limit",
    "thermal-writability",
    "hamr"
  ],
  "provenance": [
    "A simplified thermal-activation model; not a validated predictor of HDD bit errors or fleet failure.",
    "The cited experiment concerns an MTJ, not an HDD medium. No fitted experimental parameter is transferred into the worksheet."
  ],
  "citations": [
    {
      "id": "rippard",
      "title": "Rippard et al., Thermal relaxation rates of magnetic nanoparticles (2011), PRB 84 064439; doi:10.1103/PhysRevB.84.064439, equation 1",
      "url": "https://arxiv.org/pdf/1107.5007v1",
      "accessed": "2026-10-17"
    },
    {
      "id": "hesela-retention",
      "title": "Hesela: Magnetic retention: why 60 kBT is not an expiry date; explicit two-state worksheet, not measurements",
      "url": "https://hesela.com/analyses/magnetic-retention-time-and-probability/",
      "accessed": "2026-10-17"
    }
  ]
}