into the magnetic fi eld, making it appear heavier. Oxygen
is a paramagnetic substance because it has two unpaired
electrons: this property is used to detect the concentration
of oxygen in incubators. All radicals are paramagnetic.
Many compounds of the d-block elements are paramagnetic
because they have various numbers of unpaired d-electrons.
The modern approach to measuring magnetic properties
is to use a superconducting quantum interference device
(a SQUID), which is highly sensitive to small magnetic fi elds
and can be used to make very precise measurements on
small samples.