hesela.devNeel-Arrhenius model
The Neel-Arrhenius model describes thermally activated magnetic reversal with an exponential dependence on the ratio of an energy barrier to thermal energy.
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 [1]. Attempt rates are model and device dependent.
Do 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 [2].
Relations
- related
- magnetic-thermal-stability-factor, superparamagnetic-limit, thermal-writability, hamr
Citations
- Rippard et al., Thermal relaxation rates of magnetic nanoparticles (2011), PRB 84 064439; doi:10.1103/PhysRevB.84.064439, equation 1
- Hesela: Magnetic retention: why 60 kBT is not an expiry date; explicit two-state worksheet, not measurements
Sources & caveats
- 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.