I was at AES this week, and talked to some folks at Beyer and Shure to get definitive answers for the questions that came up here about their microphone magnets.

1- The Shure SM57 uses an Alnico magnet.

2- The Beyer M201 started out as an Alnico, but was transitioned to NIB ("Neo") about five years ago. There was no announcement of this, nor any change in the model designation. The Beyer engineers were quite confident that the tonality and response of the 201 was not altered, other than a small increase in sensitivity. FWIW, I said that I thought it would be tricky to increase the sensitivity without changing the low-frequency damping (since BL effects both), but the two engineers I spoke with assured me that this was considered, and compensated by slight alterations in the magnetic circuit. I didn't fully understand, but it was not the venue for this kind of deep discussion, and I trust their end results. (If anyone wants to loan me a known-good, old M201, I'll measure it against some of the more recent ones I have and report.)

I also asked several other mic designers I know about the kind of magnet materials they worked with. It's all either NIB or Alnico these days, and it was pretty much all Alnico in the decades prior. Of course, there are a range of formulations for both Alnico and NIB. There was some vague recollection of Samarium-Cobalt being popular for a brief time before NIB became affordable, but nobody could remember any specific, popular models that used it.