Diamagnetism with Bismuth stabilises levitation
Diamagnetic levitation using bismuth plates to stabilise the magnetic lift of one permanent magnet by another. This is the classical setup with a small cube magnet between two bismuth plates. “Continue Reading” to see the video, a cool Bismuth crystal, 6 photos and links…
A large magnet well above provides the lift and a fairly uniform field and the bismuth plates help stabilize the area locally. Without the diamagnetic repulsion (or other tricks), Earnshaw’s theorem states that this cannot be stable. Note that this is permanent levitation without external power.
The magnet rotates freely and is quite stable in the centre. I have used 3 small bismuth cylinders as below for levitation of a small cubic NIB magnet. I have also used about 200 g of bismuth as 19 small cylindrical pellets in rows above and 19 below for large magnets but to levitate successfully the field needs to be uniform and the main lifting magnet needs to be larger and further away. They are fixed firmly with … tape.
The left photo shows the display set-up with single bismuth cylinders. The magnetic field is 4.5 mT at the top of teh gap and 3.9 at the lower end. This is a 15% field reduction. Ideally the field should be uniform to accentuate the slight diamagnetic forces. Using a large NIB magnet would allow it to be further away and hopefully have a more uniform field.
Here is another way to demonstrate diamagnetism with bismuth. A block of bismuth is suspended in the field of an electromagnet. The weight of the bismuth can be recorded with the magnetic field turned on and off.
Really I should get a life and get back to Tesla coil stuff but there are challenges here. Diamagnetic levitation with copper stabilization. This took a few hours playing with Lego to get things just right. Similar to levitation between Bismuth but 10 times harder. Had to use a really thin magnet and very close segments of copper bus-bar. Could do the same with pyrolytic graphite but I have only fairly thin segments. Not that dramatic or elegant but works.
The left photo above shows a 10 g bismuth cylinder showing a weight (with support block) of 38.96 g. The right photo shows that this reduces to 38.57 g in the electromagnet field. This is a 0.39 g or 3.9% reduction in the weight of the bismuth. It is not well optimized though. Hardly levitation as the field is not strong and also does not have a strong gradient.
A similar test but using a permanent magnet. The left photo above shows the 10 g bismuth cylinder with a weight (with support beam) of 24.38 g. A magnet is then slid underneath the bismuth. The right photo shows that this reduces to 24.16 g in the NIB magnet field. This is a 0.22 g or 2.2 % reduction.
Bismuth also is also unusually colourful when crystallised on cooling.
Related pages
Diamagnetism with pyrolytic graphite
Try something else
External links
Earnshaw’s Theorem
Diamagnetism – Wikipedia
Bismuth – Wikipedia
Photo Date: 2004