Department of Energy Argonne National Laboratory Office of Science NEWTON's Homepage NEWTON's Homepage
NEWTON, Ask A Scientist!
NEWTON Home Page NEWTON Teachers Visit Our Archives Ask A Question How To Ask A Question Question of the Week Our Expert Scientists Volunteer at NEWTON! Frequently Asked Questions Referencing NEWTON About NEWTON About Ask A Scientist Education At Argonne Free Electron Spin
Name: Nathan
Status: other
Age: N/A
Location: N/A
Country: N/A
Date: N/A

Do "free electrons" have quantized spin? ie Do electrons that are not in a quantum well (not bound to an atom in any way) have quantized states for the magnetic moment? When referring to electron spin (ie magnetic moment) is both the magnitude and the direction of the magnetic moment quantized?

Dear Nathan,

Yes, both the magnitude and direction of the spin (and so, the magnetic moment) are quantized.

The magnitude is built into the electron. The direction can only be seen by making a measurement of the component of the magnetic moment along some direction - normally the direction of the magnetic field imposed on the electron. The result for a spin 1/2 electron can only be "up" =+1/2 (parallel to the magnetic field) or "down = -1/2 (antiparallel to the magnetic field).

The magnetic moment can be measured by measuring the rate of rotation of the magnetic moment while in a magnetic field perpendicular to the electron spin.

Best, Dick Plano, Professor of Physics emeritus, Rutgers University

Click here to return to the Physics Archives

NEWTON is an electronic community for Science, Math, and Computer Science K-12 Educators, sponsored and operated by Argonne National Laboratory's Educational Programs, Andrew Skipor, Ph.D., Head of Educational Programs.

For assistance with NEWTON contact a System Operator (, or at Argonne's Educational Programs

Educational Programs
Building 360
9700 S. Cass Ave.
Argonne, Illinois
60439-4845, USA
Update: June 2012
Weclome To Newton

Argonne National Laboratory