Yes, that's exactly what these are, solid NMR samples. I sure haven't heard of 70K RPS, and since we have some pretty strong magnets, I doubt anyone is doing 70K RPS. The spin speed scales with the strength of the superconducting magnet field. I think our strongest one is almost 10 T, and few go above that.
Any idea what the tensile strength of calcite is? I note the comment from one of the investigators: "The rotation rate is so fast that the angular acceleration at the sphere surface is 1 billion times that of gravity on the Earth surface? it's amazing that the centrifugal forces do not cause the sphere to disintegrate!".
Somewhat OT, but around 50 years ago I remember looking through a textbook of electronic circuits, published in the mid-50s. IIRC, one was used to spin a small aluminium rod, I think about 10 mm long and 5 mm across (hexagonal cross-section), to 5 million rpm in a vacuum. The rod was levitated above a coil by a magnetic field, and another coil applied a spin to it. It's many years ago, so my memory may be incorrect, but I think it took at least 2 hours for the rod to reach maximum speed. Is that possible, or is my imagination working overtime?!
Sounds reasonable. The torque you can get that way isn't that big, unless you have a lot of iron (as in a squirrel cage motor).
Small single crystals can be quite a bit stronger than bulk material, especially if they're prepared so as to have a very smooth surface. (It's the largest crack that limits the ultimate strength, just like the proverbial weakest link in a chain.)