Permanent magnets have a large coercivity field in common, and as far as I know, this phenomenon is closely related to large magneto-crystalline anisotropy. In order to maximize magneto-crystalline anisotropy, the material would have to be single crystal, right?
I wonder if most permanent magnets on the market are single-crystal.
And additionally, in general, it is known that magnets are difficult to align in the shallow width direction(due to the influence of shape anisotropy). I wonder how thin it should be to be comparable to magneto-crystalline anisotropy, is there any reference about the detail energy comparison?
Thanks in advance for any help you can provide.
Magnets are not single crystal. They are made of a powder which may be largely single crystal for each particle, or with domain pinning due to large discontinuities, then the particles are sintered together or glued in a matrix in a magnetic field to align them, or with pressure applied to align them, if the particles are flat, as ferrites often are.
Alnico is old fashioned and used to grow long needles of Nickel cobalt in an aluminium matrix. Even these weren't single crystal but used shape anisotropy to resist demagnetisation.
Permanent magnets are made from ferromagnetic alloys (Fe, Ni, Co, and also some rare earth metals).
The ferromagnetic materials are hard magnets.
https://imamagnets.com/en/blog/what-is-permanent-magnet-types/
No permanent magnets are definitely monocrystalline. The common ferrite ones are formed from a powder of irregular, oval BaFe12O19 or SrFe12O19 (Ba or Sr hexaferrites) particles, which are pressed and subsequently magnetized. Rare earth elements magnets are mostly made of Nd2Fe14B (Nd-Fe boride) particles. The particle composition in non-magnetized magnets can be easily observed in SEM. Given the limited size and stability of magnetic domains, the idea of a monocrystalline character loses its meaning. Sorry.
Alloy based magnets are a rarity, they are designed for special uses. The division of magnets into hard and soft actually refers to the shape of the hysteresis curve, respectively the coersive force.
Dalibor Matýsek Thank you for your reply, could you please explain "Given the limited size and stability of magnetic domains, the idea of a monocrystalline character loses its meaning" more detail?
I understood that single crystalline permanent magnet is impossible due to the influence of magneto-static energy that preferred multi-domain, but did I understand correctly?
@Jangwoo Ha Yes. The size of magnetic domains is limited. Even with a single crystal, multiple domains are arranged.
Check https://lib.dr.iastate.edu/cgi/viewcontent.cgi?article=1327&context=ameslab_manuscripts
https://www.sciencedirect.com/topics/physics-and-astronomy/permanent-magnets
Check on this web
https://www.semanticscholar.org/paper/Single-Crystal-Permanent-Magnets%3A-Extraordinary-in-Lamichhane-Onyszczak/822af810f24831375545fbce23ec2edfa68c4ba9
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