That is a rather small diameter for a magnetic bearing. Especially a passive one.
You cannot have an entirely passive all-magnetic bearing. There is some sort of a principle (different names are being used) that says that an all magnetic bearing does not work. So, you either need a mechanical support somewhere. Usually a point contact at the end of the shaft or a "self-generating" eddy current stabilizing bearing. Or an active magnetic bearing.
But, as said, the diameters are small. Is there room for larger bearings? What speed range is your application? Ever considered air?
You are probably thinking about Earnshaw's theorem.
I don't think it applies. For one thing you have spinning shaft which is not a static condition and the relative motion can be used to induce currents. For another thing, there are a number of tricks that can be used to get around it. Strange things happen when you use a superconductor.
I wouldn't call a superconducting device "passive". You have to keep it cold, and for that you need energy.
And, no, magnetic bearings do not work with at least one support. That can be a self-generated current in a coil, but then again, it is getting active - in a way - although with no electronics. That is the "self-generating" eddy current stabilizing bearing that I was referring to in my post.
Tests with that kind of bearings show that they get quite hot. And that's no wonder.
Do you have hands-on experience with this bearing type? At what speeds? My experience is not so positive. There was a Canadian company that had some co-operation with SKF some years ago. Have been using air instead. But even air is getting quite "hard" when speed gets high. Good for low speeds, though.
