In a few textbooks I've read that Quantum Spin (which is indeed intrinsic) only 'reveals' itself in the presence of a magnetic field. This seems very odd (but let's be honest, it's quantum mechanics) and I was wondering, is there an experiment that validates this? I've looked and haven't been able to find anything. The only experiment that I could think of is a Stern-Gerlach-like device where $B=0$, but $d B/d z \neq 0$.
Revealment of the electrons intrinsic spin:
Lorentz force: Deflection of an electron, moving nonparallel to an external magnetic field.
Pauli’s exclusion principle: Electrons in atomic shells couldn’t have identical quantum numbers, at least the spin quantum number has to be different. The electrons with otherwise identical numbers have to have opposite spin (and opposite oriented magnetic dipols).