Do you have a source for this? I don't believe it is true. Diamagnetism is a fundamental quantum mechanical property related to the quantum mechanical analog to the Lorentz force. Spin 1/2 electrons have exactly 2 states: opposing or attracting a static magnetic field, regardless of direction of the field or orientation of the particle.
When all electrons are paired (and the spin fields cancel), all that is left is that Lorentz force and you get diamagnetism. Otherwise, you generally get paramagnetism (attractive because of the net dipole created by net spin).
When all electrons are paired (and the spin fields cancel), all that is left is that Lorentz force and you get diamagnetism. Otherwise, you generally get paramagnetism (attractive because of the net dipole created by net spin).
See the Stern Gerlach experiment: https://en.wikipedia.org/wiki/Stern%E2%80%93Gerlach_experime...