Magnet

[labview1958]

Is my maths correct?

 

Let's say each bar magnet has 1 Tesla. Then 10 bar magnets put together would have 10x0.1 = 1 Tesla

 

Is it right? Can I get 1 Tesla?

[swansont]

Is my maths correct?

 

Let's say each bar magnet has 1 Tesla. Then 10 bar magnets put together would have 10x0.1 = 1 Tesla

 

Is it right? Can I get 1 Tesla?

 

 

I'm not sure what you're going for here. If one magnet has 1 Tesla, you don't need to do anything else to get 1 Tesla.

[Megatron]

Heh, if you're looking for magnets capable of magnetic flux densities approaching or attaining 1 Tesla or higher, just ask SuperMagnetMan at this site:

http://www.engconcepts.net/

[Meir Achuz]

"Is my maths correct?

Let's say each bar magnet has 1 Tesla. Then 10 bar magnets put together would have 10x0.1 = 1 Tesla

Is it right? Can I get 1 Tesla?"

 

I guess you meant each magnet has 0.1 T.

But, no. Placing magnets end to end do not add up the field.

200 magnets, each of 0.1T, placed end to end would give 0.1 T.

[labview1958]

Is there a way of placing 10 magnets of 0.1 Tesla each to get a total of 1 Tesla? If not 1 Tesla do we get 0.2 Tesla?

[swansont]

Is there a way of placing 10 magnets of 0.1 Tesla each to get a total of 1 Tesla? If not 1 Tesla do we get 0.2 Tesla?

 

I explained this in post #24. It will work if you can find a material that has a high enough permeability to concentrate the flux lines but not so high that you saturate the material.

 

If you try this with multiple magnets, you also have to be able to keep the magnets close enough together, with all the poles in the same direction.

[labview1958]

If the mu-material is iron, it would shield the magnetic field. Thus the field would be weaker above the mu-material. I assume the field would also be weaker on the side of the mu-material.

[swansont]

If the mu-material is iron, it would shield the magnetic field. Thus the field would be weaker above the mu-material. I assume the field would also be weaker on the side of the mu-material.

 

High mu materials can shield magnetic fields because they concentrate the fields inside of them. You can use that feature to your advantage.

[DQW]

Why do only iron , nickel and cobalt can be striked to be become a magnet ?

Fe, Co, Ni, Gd are the only elements that are ferromagnetic at RT (Gd, on a cool day)

 

Why do other element cannot?

Because they are different. Ferromagnetism comes from an exchange interaction between the electrons in the material. If the magnitude of the exchange interaction is large and positive, you have ferromagnetism. If it's large and negative, you have antiferromagnetism. If it's very small, you have neither.

[DQW]

Manganesse is also atracted to magnets, and if you look at a PTOE they`re all side by side too

No it's not. Mn is antiferromagnetic.

[DQW]

What else can be used to make magnet?

If you don't stick to pure elements (why should you ?) the best permanent magnets are made of rare earth-transition metal intermetallic compounds. Look up NdFeB (popular name for Nd2Fe14B) and SmCo5. Some transition metal alloys are fairly good too : look up AlNiCo.

[DQW]

It's surprising how even rather simple para- and diamagnetics end up in the zone of "We don't know yet and perhaps never will". And that's exactly what's great in quantum mechanics, there always seems to be something to find out.

Paramagnetism and diamagnetism are extremely well understood, thanks to work done by people like Langevin, Curie, van Vleck, Pauli, Anderson and others.

[DQW]

Diamagnetic materials have electrons whose dipoles align with the external field. Paramagnetic materials' dipoles anti-align.

It is the other way around.

[DQW]

...also apparently placing a magnetic field near a superconductor will destroy the superconductor's superconductiveness (I'm not sure if it's temporary, ie. whilst the magnet is there or more permament).

This is true. The superconductor goes "normal" in the presence of a field exceeding the critical field, Hc. In a Type II superconductor, there is an intermediate phase - the Abrikosov phase - bounded by two critical field curves : Hc1(T) and Hc2(T), where fields penetrate the bulk through lines known as flux vortices.

[5614]

No it's not. Mn is antiferromagnetic.

I can't prove you wrong, but I know that MnO is antiferromagnetic and that Mn2+ ions are antiferromagnetic and that Mn can be ferromagnetic but only after special treatment... Are you certain just normal (non-ionised/reacted/treated) Mn is antiferromagnetic?

[DQW]

The Neel Temperature for Mn metal is 95K; it orders antiferromagnetically (AFM) only at low temperatures. Above this, it is a regular Curie paramagnet.

 

A quick search gave me this hit : http://chemistry.anl.gov/ClusterStudies/images/Mnn-atom.pdf

http://chemistry.anl.gov/ClusterStudies/SpectroscopicAndStatic.html

 

If that's not sufficient I can find you a better reference later.

 

Bulk Mn is AFM for a completely different reason than that which makes MnO, MnF2 and other such compounds AFM.

 

The bulk metal is AFM because of the lattice parameter in the crystal being suitable for ensuring a non-negligible overlap between the valence electrons of nearest neighbor atoms in addition to exchange mediated by conduction electrons. This (first part) is explained thorugh the Direct Exchange mechanism, originally porposed by Heitler and London, (for simple diatomic molecules) and subsequently improved upon by Freeman, Watson (Phys Rev 124, 1439-1451 , 1961) and later (the second part was included and the ordering was) extended to metals by Stoner and others.

 

Mn2+ based compounds are AFM because of Superexchange : hopping of the spin paired 2p electrons of the liganding anion (O2-, F-, etc) reduces energy due to delocalization; since the 2p electrons in a subshell are antiparallel, hopping is permitted (by an extension of Hund's First Rule) only if the neighboring Mn2+ ions are also spin-antiparallel - hence the ground state is AFM (note : that's a naive explanation, but it catches the essense of the mechanism very nicely).

 

The reason manganese is called that, (the Latin origin is from magnes which essentially means 'magnetic') is because it was first extracted from the ore pyrolusite which is ferromagnetic. And yes, manganese can be made ferromagnetic too, by making it nanocrystalline, or in the form of thin films (and possibly in other ways too - I really don't know anything about that).

[labview1958]

I have been playing around with different types of magnets. I have used two identical cylindirical magnets to fiind the repulsive force between them for various separation distances. I have also used rectangular magnets for similar purposes. Also I have used other shapes like square etc. What I found was that

 

F = Aexp(-zx) which is an exponential curve

While most textbooks say it should be F=AX^z which is a power series.

 

where F = repulsive force and x = distance between magnets.

 

The expression F = Aexp(-zx) is valid for the repulsive force between a bulk superconductor and a magnet. It should also be valid for repulsion between identical magnets.

[DQW]

It's hard to tell much unless you specify the experimental conditions better (there's one particular piece I'm looking for). Think about what are all the important pieces of information you need to convey about your experiments and write down any that you've missed.

 

(Let this serve as an exercise in communicating/reporting results of a scientific experiment)