I was told that if you put a spin 1/2 particle in a magnetic field, it will align with or against the field. But some places it also says that it will precess around the field. Which one is right?
So I had it backwards? The spin is intrinsic, and the magnetic moment is defined using the spin - since spin is a type of angular momentum.Spin up and spin down are not defined using magnetic moments. They usually mean the z-component of the spin vector (expectation) is +hbar/2 or -hbar/2 for up or down respectively.