A What is spin relaxation?

Hello,

Im not sure if get the meaning of spin relaxation. In the case, if you have a spin polarized current, what happens there if you talk about spin relaxation? Is it just the phenomena that after some time the spins will pointing in all direction?
If that is right why that happens?
 

ZapperZ

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Hello,

Im not sure if get the meaning of spin relaxation. In the case, if you have a spin polarized current, what happens there if you talk about spin relaxation? Is it just the phenomena that after some time the spins will pointing in all direction?
If that is right why that happens?
It's the decay of a net magnetization.

Why? Because of many things, such as the individual spins are in different external or inhomogeneous field. This is why, for example, in NMR, there is a spin-lattice relaxation and spin-spin relaxation rates. Each of the individual spins are in different environment, and they are not strongly coupled to one another.

Think of it. If they all started out as not being aligned, and then they were aligned by some external field, and then the field is switched off, if they are not strongly coupled to one another, why should they continue to be aligned?

Zz.
 

Henryk

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Go back to classical physics. There is a spinning body, a torque applied at an angle to the axis of the spin, the net result is a precession of the axis of the spinning body.
Back to the NMR, the spin magnetic moment is a result of a "rotation", i.e. angular momentum of some kind. Apply a uniform magnetic field, this produces a torque that is a vector product of the magnetic moment (aligned with the direction of the spin) and the magnetic field. This torque will result in a precession of the axis of the spin. In the absence of any dissipation, the spin will go forever and the system would never achieve the lowest energy state - the spin aligned with the magnetic field.
Spin relaxation is just a measure of interaction between the spinning electron and it's environment that can dissipate the precession and result in the alignment of the spin with the magnetic field.
 
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Does this mean you could actually change a substance with a magnetic field, like possibly get rid of nuclear waste with the right magnetic field?
 

ZapperZ

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Does this mean you could actually change a substance with a magnetic field, like possibly get rid of nuclear waste with the right magnetic field?
No, because the nature of nuclear decay is not affected by magnetic field.

You need to find properties that ARE affected by the magnetic field. Otherwise, you are making connection between things that have no connection, such as in a superstition.

This is also getting to be off-topic. We are addressing specific issue in the OP's question.

Zz.
 
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Thanks for your opinion!
 

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