How can a magnet have a greater magnetic field strength than a bigger, heavier and more powerful magnet made of the exact same material?

Question

Here are some informations I found on the magnetic field strength (also called "magnetic flux density" or "magnetic induction", commonly denoted as B and expressed in tesla or in gauss) of an average neodymium-iron-boron rare earth magnet.

"A modern neodymium-iron-boron (NIB) rare earth magnet has a strength of about 1.25 T." http://teslaradioconspiracy.blogspot.fr/2007/11/tesla-si-unit-of-magnetic-field.html

"1.25 T – magnetic field intensity at the surface of a neodymium magnet" http://en.wikipedia.org/wiki/Tesla_%28unit%29#Examples

"1.25 T – strength of a modern neodymium–iron–boron (Nd2Fe14B) rare earth magnet." http://en.wikipedia.org/wiki/Orders_of_magnitude_%28magnetic_field%29

"The magnetic field typically produced by rare-earth magnets can be in excess of 1.4 teslas, whereas ferrite or ceramic magnets typically exhibit fields of 0.5 to 1 tesla." http://en.wikipedia.org/wiki/Rare-earth_magnet

Clearly, all of these sources agree that an average neodymium-iron-boron rare earth magnet has a magnetic field strength of about 1.25 T.

But here's the problem: I searched on every single possible websites for THE most powerful magnet that can be bought.

And THE most powerful magnet that can be bought is this one: http://www.kjmagnetics.com/proddetail.asp?prod=BZX0ZX0Y0-N52

It has dimensions of 4" x 4" x 2", a weight of 138.8 oz (3934 g) and a pull force of 1226.5 lbs.

And a magnetic field strength (surface field) of 4933 Gauss.

4933 G = 0.4933 T

Far from the value of 1.25 T that is supposed to be the magnetic field strength of just an average rare-earth magnet...

How is this possible?

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And also, I found something else very intriguing: http://www.kjmagnetics.com/proddetail.asp?prod=BZX0Z0Y0-N52

This magnet has dimensions of 4" x 3" x 2", a weight of 104.1 oz (2950 g) and a pull force of 1013 lbs.

So this magnet is smaller, less heavy and less powerful than the previous magnet.

But it has a magnetic field strength (surface field) of 5336 G = 0.5336 T which is greater than the previous magnet!

Again, how is this possible?

Note: Both magnets are made of the same material (NdFeB, grade N52). Both magnets have the same magnetization direction (thru thickness). And both magnets have the same plating/coating (Ni-Cu-Ni, Nickel).

Answer 1

To be very honest with you, I wouldn't take any of these "sources" very seriously. For one thing, the "pull force" of magnets depends very much on the properties of the ferromagnetic materials and the geometry that the magnets are "pulling". If the magnet saturates the other material (which will be the case with many types of iron yokes that these could be used with in a lifting application), then they will never even reach their full potential. The same is true if the field geometry is not optimized. Moreover, a diamagnetic material will even be repelled!

Assembling these magnets into a lifting assembly is both dangerous and difficult. If you value your digits, let a professional manufacturer of lifting magnets do it for you.

All in all, the way this company "characterizes" their product is highly unprofessional and completely useless for any serious engineering application. If you need a lifting magnet, buy a fully assembled and specified lifting magnet assembly. On the other hand, if all you want, is to lift your ego by owning a larger piece of magnetic material than your friends, you can buy way bigger and "more powerful" magnets from other manufacturers, so the claims of these people to have "the largest" is bogus. The sky is really the only limit to magnet size, if you have the money and feel a need to spend it.

And finally, since I had a chance to work with 12T superconducting magnets in my life, "my magnets were way stronger" than these tiny shrimps, anyway, and that's not even one third as "strong" as the "strongest" technical magnet designed, so far. But then, of course, nothing comes even close to neutron stars and magnetars... so if you want something really STRONG, you better start saving for a very, very long space trip.

Just my two cents...