Paramagnetism, Diamagnetism

[iScience92]

Please confirm & answer the following:

 

An atom exposed to an external B-field will experience both a torque on its orbitals (paramagnetism), and a change in orbital velocities and thereby a change in the magnetic momenta of the orbits (diamagnetism).

 

When the atom has all paired electrons, the net torque is zero so the phenomenon resulting from the change in orbital velocity dominates.

 

But, when the atom has an unpaired electron, the net torque on that orbital is non-zero. Question: So do these orbitals physically re-orient themselves to align with the B_external?

but the diamagnetic effect/influence is still present. Question: For atoms with unpaired electrons, why does the paramagnetic effect always win?

 

[Enthalpy]

The idea of velocity is very unclear and misleading for an electron in an atom. The orbital momentum is more useful.

 

The "orientation" of an orbital is not a simple idea. In each direction, for instance the direction of the external field, an orbital can have a finite set of orbital momenta.

[studiot]

Remember first that most materials are made up of molecules, not atoms.

Many, if not most, materials exhibit little or no magnetism because the atomic effects tend to cancel out when the atoms form molecules.

 

 

All materials exhibit an inherent diamagnetic effect.

When a material is put into an external magnetic field, the orbital electrons are acted on by a force which changes the orbitals in accordance with Lenz's Law.

Thus the effect is to oppose the external fied, thereby reducing it.

 

Those molecules where the atomic magnetism does not cancel possess a permanent magnetic dipole moment.

Without an external field these dipole moments are oriented randomly so again cancel.

However when there is an external field the dipoles tend to align with the field, strengthening it.

This effect is called paramagnetism.

Paramagnetism does not, of itself, change the orbitals.

 

Ferromagnetism is a particularly strong form of paramagnetism.

Edited August 5, 2014 by studiot

[iScience92]

The idea of velocity is very unclear and misleading for an electron in an atom. The orbital momentum is more useful.

 

The "orientation" of an orbital is not a simple idea. In each direction, for instance the direction of the external field, an orbital can have a finite set of orbital momenta.

 

I'm reading from Griffith's Intro to E&M as an intro to the topic/phenomenon; hence i was working with a simplified analogy.

"Orbital momenta"?

 

Considering an electron orbiting on a 2-D plane (the simplified analogy given in the book), i intuitively understand what the "oritentation of orbit" refers to, but in actuality, when you say that an orbital can have a finite set of orbital momenta in any [math]\hat{r}[/math], i take this to be a time averaged information, is this correct? If not, then at any given time t, how exactly is the orientation defined?

 

However when there is an external field the dipoles tend to align with the field, strengthening it.

This effect is called paramagnetism.

But why is the paramagnetic effect always stronger than the diamagnetic one? Is there a qualitative explanation?

Edited August 6, 2014 by iScience92

[Nicholas Kang]

Dear iScience92,

 

I think you can refer to wikipedia in this context. Diamagnetism produce a magnetic field which oppose the externally applied magnetic field. I mean the magnetic field obeys the Lenz`s Law. This effect is clearly seen in electromagnetic induction, if I recalled correctly. Eddy currents on conductors produce the same effect too. If I place a rotating aluminium plate in a magnetic field, it will soon stop its rotating motion, simply because the magnetic field induce a current on the plate. The current then generates its own magnetic field, and this oppose the externally applied magnetic field by the magnet itself.

 

Refer http://en.wikipedia.org/wiki/Paramagnetism and http://en.wikipedia.org/wiki/Diamagnetism

 

I think paramagnetic effect is always stronger than diamagnetic effect because paramagnetic effect occurs from the object-paramagnetic object itself, which is a normal magnetic field, while diamagnetic effect would be weaker simply because it oppose the field and thus heat might loss to the air during opposition. I think you can refer to studiot for a detailed explanation.

 

In case you don`t know, Lenz`s Law is obeying Law of Conservation of Energy. When a n-pole object is placed near a conductor, the point near the magnet would be north too to produce force of repulsion. The force times the distance travelled will become the work to push the conventional current around the curcuit, and when it is removed from the conductor, force of attraction would exist, which induce a south pole on the conductor that produce a force to "pull' the electrons back thus the current is reversing. Continuing this push and pull motion would induce an AC current on the conductor-a basic model of AC generator.

[studiot]

 

But why is the paramagnetic effect always stronger than the diamagnetic one? Is there a qualitative explanation?

 

 

A qualitative explanation?

 

First to remember that the applied field and the field due to the material add (vectorially) to form the total field.

 

This diagram may help.

 

For diamagnetic materials there is no material field so the magnetic moments a zero without an applied field as shown in the first diagram.

 

If we apply an external field the induced moments oppose the applied field reducing its intensity as shown in the second diagram.

 

For paramagnetic materials there is a material field that averages zero without an applied field because every molecule has a random orientation.

 

When we apply a field to a paramagnetic material all the random molecular moments align with the field, reinforcing it and increasing its intensity.

 

Paramagnetic materials also exhibit diamagnetism, but paramagnetism and diamagnetism spring from a different mechanisms and the numbers just work out that paramagnetism is quite a bit stronger so with paramagnetic materials the diamagnetic effect is masked.

 

 

 

[Nicholas Kang]

You should follow studiot`s explanation. studiot, am I wrong?

Nice picture drawing.

[irvin hernandez]

The idea of velocity is very unclear and misleading for an electron in an atom. The orbital momentum is more useful.

 

The "orientation" of an orbital is not a simple idea. In each direction, for instance the direction of the external field, an orbital can have a finite set of orbital momenta.

if an atom dies does it becomes anti matter? what happens when an atom stabilizes or its orbital plays out its set of moments? does it cease to exist or become dark matter (dead space)? can dark matter be manipulated (or can it be revived after x number of orbital moments is played out?) what can revive the orbitals? just tryin to get some info. i got this off concept and i need as much info on this. i came here for magnetism but im tryin to educate myself in this, thought id ask someone more experienced in this department.