I am a student that's very new to magnetism in general and I've been reading/learning for the past few weeks.

I'd like to build magnetic tweezers to use in materials with kPa order stiffness - so I would need very high fields and gradients.

However, from the little I understand, it looks like if I use ferromagnetic particles with the magnetic tweezers, the forces applied only depend on the field gradient? Torque doesn't matter to me - I just need to observe the displacement of the particles.

My main question and source of confusion is the following:

How do I generate very high/steep magnetic field gradients? Do I automatically need very high fields in order to have steep gradients?

I've done a lot of searching and all I could really find was a Helmholtz/Maxwell coil pair. I was wondering if there were any other ways to generate a very steep magnetic field gradient?

I am also open to using permanent magnets.

Thank you!


Sounds like a cool project!

Historically, a strong gradient of the type you describe was required for the Stern-Gerlach experiment, for very similar reasons. They used a permanent magnet with one flat pole and one sharp pole, like this: shaped magnet poles

For more detail, see an example at the end of ch. 11 of my book Simple Nature.


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