# What causes magnetism?

Electric fields are caused by particles that have charge. Gravitational fields are caused by particles that have mass. What is the property of a particle that causes it to interact with a magnetic field?

I've read that magnetic fields are caused by charged particles that are moving in an electric field. However, since any charged particle in an electric field experiences a force on it which causes it to move, doesn't this mean that an electric field is impossible to detect without a magnetic field also being present, and vice versa? How would a magnetic field and electric field differ in this case?

I've also read that magnetism is caused by groupings of particles with the same spin state. Is this the quantum mechanical explanation, and if so then how do groupings of such particles create a magnetic field?

• Commented Aug 3, 2017 at 11:16
• so basically you look at the lone pair. If there is only one electron (spin up/down) then it is a paramagnetic material or even ferromagnetic if it has 2 electrons in the lone pair then the magnetic fields cancel and you have diamagnetism. At very high magnetic field strengths diamagnetic materials even get repulsion so strong you can levitate things (see frog levitating on youtube). For Ferromagnets the particles align on a macroscopic level and we get large fields (yes the nuclues also has a smaller magnetic moment based upon once again if there are any odd number of proton or neutron) Commented Jan 2, 2021 at 16:42

If all the spins are aligned, then a magnetic field is created. It is the direction of the spin that causes the attraction or repulsion (As far as my understanding goes)

An electric field can be created by a stationary charge (electrostatics). It is only when this charge moves that the magnetic field is created.

• How do bar magnets work then. Is there any moving charge within them? Commented Aug 3, 2017 at 10:38
• Nope, nice and static, just aligned spin! If you get a sheet of paper and draw a load of loops moving in a clockwise direction inside a bar magnet (to model the spins) you should be able to see how them aligning creates a general field Commented Aug 3, 2017 at 11:21
• Commented Aug 3, 2017 at 11:24
• Or you can do the classic experiment with a bar magnet and a compass - if you're willing to spend the time on that. Commented Aug 3, 2017 at 11:48

I will try to explain it in the simplest way that I can think of. The magnetic behavior depends on the following factors: 1)the subatomic particles present in the atom 2)atoms 3)collection of atoms 4)domains(collection of collection of atoms)

1)THE SUBATOMIC PARTICLES AND 2)ATOMS Subatomic particles have some basic fundamental properties like mass, charge, etc. In the same way they also have a property called as intrinsic magnetic moment(which is basically the measure of their tendency to align with magnetic fields)and they could be basically thought of as some sort of tiny magnets that can align themselves to a magnetic field. We can not ask why they behave like tiny magnets because it is how the universe works just like how objects with masses attract each other. The intrinsic magnetic moment of protons is about 1000 times weaker than electrons and as a result, the nucleus of an atom does not have much effect on magnetism. The movement of electrons creates a magnetic field but the magnetic field of an atom is not due to all of the electrons of an atom. The electrons in the filled shells are found in pair and their magnetic field is aligned in such a way that it cancels each other. But the electrons are not found in pairs in approximately half-filled shells and their magnetic fields are aligned in such a way that they add up rather than cancel each other out, as a result, the magnetic field of an atom depends mostly on approximately half-filled shells(more accurately incomplete shells). Some magnetic atoms are those of the elements: Ni,Co,Fe,Cr,etc.

1. COLLECTION OF ATOMS : If a material's atoms are magnetic the entire material need not have to be magnetic. When a collection of atoms is taken into consideration then the following may happen:(the probability of either of them happening depends on which takes the least energy for that particular material's atoms ) A)The atoms may align their magnetic fields with each other in such a way that they add up together to create a magnetic field. When this happen the material is called ferromagnetic material like Fe(below its curie temperature). B)The atoms may align their magnetic fields in an alternating way in such a way that they cancel out each other's magnetic field. When this happens the material is called nonferromagnetic or antiferromagnetic like Cr. (even though chromium atoms are individually very magnetic but due to this they(collection of atoms) are very nonferromagnetic ) C)The atoms may arrange themselves in a messy way in such that some of them are aligned while others are not and some even cancel each other. So basically they are very feebly magnetic and are called paramagnetic materials.

2. DOMAINS(COLLECTION OF COLLECTION OF ATOMS):

The image shows a magnetised and unmagnetized piece of ferromagnetic material.

The individual blocks are the collection of atoms while the entire material consists of billions of collection of atoms each with their magnetic field pointing in different directions mostly. But when the material is kept in a sufficiently strong magnetic field then it causes the individual domains to align together into a big domain (the magnetized piece) and their individual magnetic fields add up. This is what causes magnetism.

• Non-ferromagnetic means just that: anything that is not ferro-magnetic, but the usual connotation is paramagnetic/diamagnetic. The state that you have drawn in your image b is called only antiferromagnetic. Commented Jan 23, 2022 at 11:07

In order to answer your question one must examine the smallest known magnet thus the Quantum Magnet which is the electron.

The nature of the intrinsic magnetic dipole moment of the electron has two interpretations. The Amperian thus the Ampère's law in Maxwell equations for electromagnetism where a spinning charge creates a current loop and therefore gives rise to a magnetic moment or the Gilbertian (William Gilbert) interpretation where the electron has two magnetic monopole charges (N and S) joined in a dipole formation. Both models can give the same correct predictions. As of which of the two is the physical correct and existing no one knows experimentally today.

• None of the two models is the physically correct one. There is abounding evidence that the electron is a pointlike entity with fundamental "spin". Nothing is rotating and there are also not two magnetic monopoles separated a certain distance. Commented Jan 23, 2022 at 11:10
• The "bare model" of the electron from where your interpretation of dimensionless point-like mass comes from, is a theoretical model that was described by Dirac as unnatural and totally neglects the physical "dressed" EM field nature of this particle which gives a finite charge radius to it. Since we never were able to experimentally measure the charge radius of a free electron at rest we cannot be sure about its actual dressed dimensions and only theoretically derive them. For the Reduced Compton wavelength as its charge radius 3.86E-13 m it turns out that it can physically spin at c or less. Commented Jan 23, 2022 at 11:36
• a) Who cares what is natural to whom in physics ? b) I am sure Dirac would revise his opinion if he had lived to this day and seen the age of particle colliders for particle physics. Commented Jan 23, 2022 at 11:45
• Particle colliders operate with accelerated particles and will operate anyway regardless the physical dimensions of the particles. Your argument proves nothing about the electron being actually a dimensionless point massive particle. I think the confusion rises from from the center of mass which yes is always a dimensionless point even at classical mechanics this however does not mean that the energy-mass manifold of the dressed electron does not necessarily occupy a volume in 3D space. Commented Jan 23, 2022 at 12:25