Objective:
-To show the ferromagnetic-paramagnetic phase transition in gadolinium metal at 20°C.
-To show that “permanent” magnetic properties of a material are temperature dependent.
-To describe the idea of a Curie point.
Apparatus:
- Gadolinium Sample
- Plastic tongs
- Thermos with hot water
- Beaker with ice water
- cow or bar magnet
Method:
Check whether the Gd sample acts as a ferromagnet at ambient conditions by bringing close to a permanent magnet and observing attraction. Demonstrate to the students that the Gd sample is/isn’t ferromagnetic.
If the Gd sample acted as a ferromagnet at ambient conditions, then place the sample into hot water, and keep for (at least) about 20 s. Remove the sample and demonstrate the lack of magnetic interactions by bringing close to a cow magnet.
Then, place the sample in the ice water beaker and keep for (at least) about 20 s. Remove the sample. It should have recovered its magnetism.
If the Gd sample was initially not ferromagnetic, then the cold/hot water steps should be reversed.
After the demonstration, make sure to dry the Gd sample and place back into the Ziploc bag to minimize oxidation
Notes:
- Typically the ice water is unnecessary as the Gd sample shows ferromagnetic behavior at room temperature.
- Keep gadolinium in sealed plastic container when not in use to minimize oxidation.
- Although gadolinium is not harmful to the touch, it can be harmful when ingested, so ideally avoid contact and wash your hands before eating.