# Dirac electron polarity?

according to Spin of an electron Dirac said the electron has Two possible spins if i'm correct.

Do Electrons have polarity? measurable by its Dirac spin or probabilistically by its quantum states?

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What do you mean by "polarity"? – twistor59 Jun 12 '13 at 17:05
measurable magnetic poles certainly. like in altering a electron spin by its magnetic poles instead of by its quantum states. i'm talking about Dirac electrons. – sphericsf Jun 12 '13 at 17:14
Electron is not a magnetic monopole. It has zero "magnetic" charge. – Trimok Jun 12 '13 at 17:48
@Diego Its not very clear what you are asking, so its difficult to answer your question. But yes if you are asking if electrons behave like tiny magnets then answer is yes. – Prathyush Jun 12 '13 at 18:04

An electron has a magnetic moment and it is proportional, as a vector, to the spin itself: $$\boldsymbol{\mu}_S=- g_S \mu_B \frac{\mathbf{S}}{\hbar}.$$ Here, $\hbar$ is the reduced Planck's constant, $\mu_B$ is the Bohr magneton, a helpful combination $e\hbar / 2 m_e$, and $g_S$ is the spin $g$-factor $$g_S\sim 2.00231930419922 \pm (1.5 × 10^{-12})$$ Because the magnetic moment is "essentially" the spin, the $x,y,z$ components of the magnetic moment refuse to commute with each other. But you may choose an axis, e.g. the $z$-axis, and the magnetic moment may be "up" or "down", just like the spin. It means that the electron is a "bar magnet" oriented in the North-South or South-North way in the case that the spin is up or down, respectively.