If I have a magnetic material that presents a typical hysteresis curve (M vs H), does this observation imply the existence of magnetic domains?

Can you have a hysteresis curve in a mono domain material?

  • $\begingroup$ Sure, why not? This should give a square hysteresis loop. $\endgroup$ – Pieter Jan 9 '18 at 18:47
  • $\begingroup$ Hysteresis is caused by the interaction of several domains, is a kind of friction between the domain walls as they grow/recede relative to each other. If you ignore magnetostriction so that the monodomain sample is free to change its shape then the |M(H)| will be a simple function, namely fully saturated (constant) whose magnitude is independent of |H|. $\endgroup$ – hyportnex Jan 9 '18 at 18:50
  • $\begingroup$ @hyportnex so in one domain it appears do to the rotation of the domain? $\endgroup$ – Mauricio Jan 13 '18 at 23:13
  • $\begingroup$ A single magnetic domain is a fully saturated one, all atomic dipoles are parallel; you can only change its orientation (direction) by the external field not its magnitude. $\endgroup$ – hyportnex Jan 14 '18 at 20:00
  • $\begingroup$ @hyportnex would the rotation of the domain result in a hysteresis curve? Are there any conditions, like something that restricts it from rotating too fast? $\endgroup$ – Mauricio Jan 14 '18 at 22:44

Can you have a hysteresis curve in a mono domain material?

Yes. One example is the Stoner-Wohlfarth system, a model system for single domain particles. In this system hysteretic behavior arises as a result of shape anisotropy energy competing with the Zeeman energy. The shape anisotropy prefers the magnetization to be aligned along an axis defined by the shape of the magnetic particle, while the Zeeman energy prefers the magnetization to be aligned in the direction of the field.

Importantly, the particle described by this model is single domain - interactions between domains are not required for hysteresis, so hysteretic behavior does not imply the existence of multiple domains.

  • $\begingroup$ Does shape anisotropy in SW model means that by some mechanism the particle cannot rotate freely? Why can't the preferred axis and field coincide? $\endgroup$ – Mauricio Feb 13 '18 at 14:19
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    $\begingroup$ @Mauricio: The particles in the SW model don't rotate. The SW model is a simple model of magnetic behavior, not of particle motion. This is often true for real nanoparticle systems - in experiments, nanoparticles are commonly embedded in some epoxy, or glued down during a measurement. $\endgroup$ – peytondmurray Feb 13 '18 at 17:27

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