B Can a Compass Needle be Magnetized to Any Horizontal Direction?

[Hornbein]

A compass needle can be magnetized to point to the north. Am I correct in thinking that the needle could have been magnetized to point to any other horizontal direction?

 

[Lnewqban]

It could be aligned with a stronger magnetic field.
Please, see:
http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/elemag.html

 

[Ibix]

I don't see why you couldn't magnetize a piece of iron so that its field was not parallel to the long axis.

 

[Hornbein]

I don't see why you couldn't magnetize a piece of iron so that its field was not parallel to the long axis.

Right, this is what I had in mind.

 

[Merlin3189]

But if you did that, the torque due to an external field would be much less.
I would be inclined to have a plastic disc with an arrow E-W or NE-SW or whatever you want, but keep the long magnet beneath aligned N-S.

 

[tech99]

Whilst I would agree that a bar magnet can be magnetised along its length or across its width, I don't think it is possible to magnetise it in other directions. This is because the magnetising force, if oblique, can be resolved into vectors along and across the magnet. The vector along the magnet will create more flux than that across it, so the direction of magnetisation will be slewed towards the major axis. On the other hand, magnetising the bar across its width is possible because the magnetising force will be at right angles to the long dimension and not have a longitudinal vector. In summary, the applied magnetising force will always be resolved along the axes of symmetry and this will favour the major axis.

 

[ergospherical]

Iron has a cubic crystal structure so exhibits cubic magnetic anisotropy, i.e. it takes less energy to magnetise a sample along the directions parallel to the lattice edges ("easy axes"). You can still magnetise the sample at arbitrary angles to these favoured directions, at an energy cost which goes as sin².

 

[Merlin3189]

I'm not sure whether you're saying, you can't magnetise a needle obliquely, or if you can, that it won't retain its magnetism?
If the former, could you not use five carefully shaped pieces of iron to 'fool' the magnetic field into going where you want it whilst magnetising the needle? (3 is the needle.)
And to mitigate the latter problem, use these pieces as 'keepers' ? (That might prejudice its utility as a compass! Though a compass that points on a bearing of 71.5 degrees magnetic, may not be the most useful compass in the world?)