I Direction of motion of particles with total spin under magnetic field

sal1854
Messages
1
Reaction score
0
TL;DR Summary
The magnetization force imposes paramagnetic materials to move in one direction. What about the fact that their unpaired electrons can have a spin up or down? Shouldn't they be able to move in both directions depending on the spin?
According to Chapter 8 of Griffiths' book Introduction to Electrodynamics, the magnetization force that acts on a magnetic dipole is

$$F_M=\nabla (m \cdot B)$$,

where ##m## is the magnetic moment and ##B## is the magnetic field.

For a paramagnetic or diamagnetic particle

$$m=\dfrac{\chi}{(1+\chi)\mu_0}B$$

where ##\chi## is the magnetic susceptibility (also shown in this wiki page [1]).

Therefore, if a particle is paramagnetic (##\chi>0##) the ##F_M## acting on it will be in the direction of the ##\nabla B^2## (and the opposite direction for a diamagnetic one)! So, all paramagnetic materials will move in the same direction?

What about the fact that the unpaired electrons of said paramagnetic particle can have a "spin-up" or "spin-down" (Stern–Gerlach experiment [2])? Shouldn't then the paramagnetic particles move randomly both "up" or "down" under the magnetization force??

Links:
[1]: https://en.wikipedia.org/wiki/Magnetization
[2]: https://en.wikipedia.org/wiki/Stern–Gerlach_experiment
 
Last edited:
Physics news on Phys.org
sal1854 said:
For a paramagnetic or diamagnetic particle

$$m=\dfrac{\chi}{(1+\chi)\mu_0}B$$

where ##\chi## is the magnetic susceptibility (also shown in this wiki page [1]).
That's only true for particles without a permanent magnetic moment. What you get then is a field-induced magnetic moment.

If a particle has a permanent magnetic moment, then usually only this moment need be considered (unless the external field is very strong).
 
Last edited:
  • Like
Likes vanhees71 and topsquark
Not an expert in QM. AFAIK, Schrödinger's equation is quite different from the classical wave equation. The former is an equation for the dynamics of the state of a (quantum?) system, the latter is an equation for the dynamics of a (classical) degree of freedom. As a matter of fact, Schrödinger's equation is first order in time derivatives, while the classical wave equation is second order. But, AFAIK, Schrödinger's equation is a wave equation; only its interpretation makes it non-classical...
I asked a question related to a table levitating but I am going to try to be specific about my question after one of the forum mentors stated I should make my question more specific (although I'm still not sure why one couldn't have asked if a table levitating is possible according to physics). Specifically, I am interested in knowing how much justification we have for an extreme low probability thermal fluctuation that results in a "miraculous" event compared to, say, a dice roll. Does a...
Insights auto threads is broken atm, so I'm manually creating these for new Insight articles. Towards the end of the first lecture for the Qiskit Global Summer School 2025, Foundations of Quantum Mechanics, Olivia Lanes (Global Lead, Content and Education IBM) stated... Source: https://www.physicsforums.com/insights/quantum-entanglement-is-a-kinematic-fact-not-a-dynamical-effect/ by @RUTA

Similar threads

Replies
0
Views
763
Replies
10
Views
4K
Replies
12
Views
3K
Replies
2
Views
2K
Replies
1
Views
2K
Replies
5
Views
4K
Replies
5
Views
3K
Back
Top