[geordief (OP)]

I see that a single atom can be described as a magnet,

https://phys.org/news/2017-03-ibm-world-smallest-magnet.amp


Is it possible to go smaller?

What if two (or 3?) individual  electrons interact with each other?

Do they create a magnetic field?

Can one group of electrons be considered as a "magnet" to the other ,single electron?

Does the interaction of 2 or more electrons always (ever?) produce em radiation?

[Kryptid]

A single, electrically-charged subatomic particle would probably qualify as a magnet of sorts: https://en.wikipedia.org/wiki/Electron_magnetic_moment

[geordief (OP)]

A single, electrically-charged subatomic particle would probably qualify as a magnet of sorts: https://en.wikipedia.org/wiki/Electron_magnetic_moment

Thanks for the link (very hard going for me)

So does a single electron have its own magnetic field as well as an electric field?

Can a single electron be a source of em radiation ?

Can a number of electrons be such a source if their fields interact ?(do fields interact  or do they perhaps just add?)

[chiralSPO]

So does a single electron have its own magnetic field as well as an electric field?

yes

Can a single electron be a source of em radiation ?

My understanding is that a single electron in an otherwise empty universe would not be able to emit EM radiation, unless it were accelerating (but then why would it be accelerating?).

But just a single electron in the presence of an external electric or magnetic field can emit (and absorb) EM radiation. This is the basis of EPR (also called ESR).

Can a number of electrons be such a source if their fields interact ?(do fields interact  or do they perhaps just add?)

Yes. Essentially all electric and magnetic fields you have ever heard about, experienced, or probably even thought about, are due to the interactions of a number of electrons's electric and magnetic fields. (The major exception here being NMR or MRI, which also involves the magnetic properties of atomic nuclei).

[evan_au]

Is it possible to go smaller? (than an electron)

Electrons behave like waves, and tend to smear out to around the size of an atom.

Much smaller than an atom is a proton, which has its own charge and angular momentum (or "spin"). This means that a proton has a magnetic field, too.
- As ChiralSPO mentions, the magnetic field of the proton is used in MRI machines to image soft tissues in the body.
- Because both the electron and the proton have a magnetic field, there is a small difference in energy depending on whether these two magnetic fields align or not. Radio astronomers use the "21cm hydrogen line" to map the normally-invisible clouds of neutral hydrogen in our galaxy. This is how they discovered the spiral arms of our galaxy.

See: https://en.wikipedia.org/wiki/Hydrogen_line
https://en.wikipedia.org/wiki/Magnetic_resonance_imaging#Mechanism

[geordief (OP)]

Is it possible to state that the magnetic field is a property  of the electric field ?(ie  the latter is  is more fundamental than the magnetic field)

Or can it rather be said that magnetic fields arise when charges are in relative motion and electric fields arise when charges  are static? (so no "hierarchy" exists between the two phenomena)

[evan_au]

no "hierarchy" exists between the two phenomena

This would be the more correct interpretation.

The relationship between electricity and magnetism was first comprehensively defined by Maxwell. He combined a number of previous discoveries into a compact mathematical statement, which today is described as 4 equations, where E is the Electric field and B is the magnetic field. They can be loosely translated as:
#3: ∇ x E = ∂B/∂t : Changes in a Magnetic field produce an Electric field
#4: ∇ x B = μ₀(J + ε₀∂E/∂t ) : Changes in an Electric field produce a Magnetic field
#1 and #2 are more about unchanging (static) electric and magnetic fields

See the right-hand column at: https://en.wikipedia.org/wiki/Maxwell%27s_equations#Formulation_in_SI_units_convention

Einstein was able to resolve some paradoxes that arose from Maxwell's equations, by adding in the effects of high speed and intense gravity.
- As I understand it, Einstein showed that a static magnetic field produced by one observer would appear to have a component of electric field to someone traveling past at high speed.
- And also that a static electric field produced by one observer would appear to have a component of magnetic field to someone traveling past at high speed.
- So electric and magnetic fields are very symmetrical
- They are described as a single field, electromagnetism