Iridium as a coating for magnets
I got this idea from fountain pens, the tip on the nicest ones is iridium.
Basically I wonder/suggest coating an implantable magnet with iridium.
other metals include iridium-platinum alloy, simply platinum and iridium-oxide.
All of these are very expensive metals, but a coating is quite thin and even if a magnet is an astronomical 500USD over 5 years for it would be under 30¢ a day and possibly guarantee safety.
Iridium platinum and plain platinum is already widely used in medical implants
These people say Iridium is the most corrosion resistant metal
https://www.americanelements.com/iridium-nanoparticles-7439-88-5
These people think its a such good idea to use iridium-oxide that they want to stop others from doing it
https://patents.google.com/patent/US20080183260A1/en
One issue other than cost would be sticking it on the magnet.
Comments
I meant to add my thoughts to this earlier, but I forgot until I saw your post on DT. I think a platinum iridium alloy would be an awesome coating for a magnet! I also think that getting a business to do the coating for you in small batches, or doing it yourself, would be prohibitively expensive and/or exceedingly difficult.
It seems from my cursory research that Iridium coatings are commonly applied using physical vapor deposition(PVD). This is the same process that is used for TiN, and would likely suffer from the same drawbacks. PVD happens at very high temperatures, so the magnets need to be re-magnetized afterwards. This puts a huge amount of stress on the magnet. You mentioned in your DT post that one issue with TiN coated magnets is the tiny pinholes that are often present. My understanding is that these pinholes and micro-cracks occur during this re-magnetization step.
You also mentioned electroplating in your DT post. Many metals can be electroplated, but it seems that Iridium is a particularly difficult one to get right. This article details some attempts to find the right electrolyte for the job, with limited success:
http://iopscience.iop.org/article/10.1088/1757-899X/181/1/012041/pdf
That's all I found on the subject. Let me know if you find out anything cool.