hesela.devMagnetic coercivity
Magnetic coercivity is the reverse field strength at which a specified magnetic quantity reaches zero on a hysteresis curve traced from saturation.
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 [1]. Since J = mu_0 M, J and M share a zero crossing; the B convention can differ because B = mu_0 H + J [4].
Remanence 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 [2]. A coercivity value is therefore not the anisotropy energy density or a thermal-retention barrier.
TDK Headway describes HAMR optical heating as temporarily reducing media coercivity so a magnetic head can write [3]. State temperature, field direction and measurement conditions when comparing values; a static hysteresis result alone does not determine recording errors during a heating pulse [5].
Relations
- related
- Heat-assisted magnetic recording (HAMR), Magnetic anisotropy, Magnetic thermal stability factor, Exchange-coupled composite media
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.
Citations
- IEC 60404-7:2019, sections 3.1-3.2 and 4: coercivity definitions and saturation (official SIST preview)
- NIST muMAG Standard Problem 2: coercivity, remanence and geometry-dependent reversal
- TDK Headway: Technologies, HAMR discussion of optical heating and media coercivity
- H. Foell, Kiel University: Magnetic Materials, section 4.1.4, relations between B, H, J and M
- Evans et al.: Thermally induced error: density limit for magnetic data storage, APL 100, 102402 (2012), doi:10.1063/1.3691196, equations 1-2
Sources & caveats
- 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.