"Strength" of magnets: is there really such a thing?

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Discussion Overview

The discussion centers around the concept of magnetic strength, particularly comparing the strength of different types of magnets, including lodestone, iron magnets, and neodymium magnets. Participants explore how magnetic strength is measured and the factors that influence it, such as material composition, shape, and measurement conditions.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant expresses uncertainty about how to measure the relative strength of magnets and proposes two methods for assessment: force required to separate two magnets and current induced in a wire loop moved along a magnet.
  • Another participant mentions that raw magnetic strength is measured in Gauss, which considers area and shape, and provides a link for further reading.
  • A different participant notes that magnet retailers quantify strength by pull force, defined as the force needed to separate a magnet from a flat surface.
  • Some participants highlight the necessity of specifying multiple factors, such as field strength and measurement distance, to accurately describe magnetic strength.
  • One participant suggests that varying grades of magnets within each material complicate the question of relative strength, mentioning concepts like magnetic saturation and maximum magnetic flux density.
  • Another participant points out that the original question lacks clarity regarding the factors that determine magnetic strength, including size and mass.

Areas of Agreement / Disagreement

Participants generally agree that measuring magnetic strength is complex and depends on multiple factors. However, there is no consensus on the specific relative strengths of the magnets mentioned, and the discussion remains unresolved regarding definitive comparisons.

Contextual Notes

Participants note that the shape and size of magnets, as well as the specific conditions under which strength is measured, are critical to understanding magnetic strength. There is also mention of the variability in grades of magnets affecting their strength.

JeffEvarts
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Ever get a simple question that leads you down a rabbit hole?

A friend of mine asked me "how much stronger are rare Earth magnets than regular iron magnets", and I was given pause for thought, since I realized that I didn't really know much about how the relative "strength" of magnets are measured. I can now assure you that googling for "magnet" or "rare Earth magnet" is the path to madness and pain. Wikipedia's content is useful, but reading the entry on Oersted requires more physics than I remember.

The above search for data did seem to indicate that different materials do make stronger magnets. I was not suprised.

But various comparatives of magnetic strength have apparently unrelated data: A "small" magnet, a "refrigerator" magnet, etc.

I came away wondering "what DO we mean when we talk about how strong a magnet is", and I came up with two organic ways of thinking about it:

  • Suppose you had two cubes that were magnetic, and they were joined at their face. The amount of force required to separate them (probably divided by the area they were joined at) would indicate how strong the magnets were
  • Suppose I had a long cylindrical bar magnet. I take a loop of wire, move it 1 meter along the magnet, and measure how many coulombs of current I drove through the circuit, modified by the resistance of the wire.

Convinced now that there is such a thing as "how strong is a magnet", that materials can make a specific difference, and that this is probably not related to size or configuration, I proceed with my question:

Presuming maximum "magnetization" of the material and identical physical configuration, what is the relative magnetic strength of:
  1. A lodestone (Fe3O4)
  2. An iron magnet (Fe)
  3. A Nd2Fe14B magnet

Anyone have real (or computable) data?

-Jeff

P.S.
This seems like kind of a noob question, but some cursory searches didn't give me any clear answers.
 
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IIRC Oersted is specific to motors and generators being defined as a dyne per unit pole. AFAIK, raw magnetic strength is measured in Gauss, one Maxwell/cm^2. Gauss takes into consideration area and therefore physical shape and therefore any focusing because of it, as opposed to dissipation.

Even if I am off a bit you may find this helpful
http://en.wikipedia.org/wiki/Orders_of_magnitude_(magnetic_field)
 
A few days ago I was looking at some magnet retailer's website. Apparently they quantify 'strength' by pull force. And they defined pull force as the force required to separate the magnet from a flat sheet of steel (or something similar). They have different types on there, and may be able to give some insight. Check out their specs page, which shows different grades and strengths, etc.
 
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Apparently enorbet and elegysix conidered my post tl;dr. Just in case other did too, let me post JUST the question I asked:

What is the relative magnetic strength of:

A lodestone (Fe3O4)
An iron magnet (Fe)
A Nd2Fe14B magnet

Anyone have real (or computable) data?
 
The problem is that you usually need two numbers to specify the strength - the field strength and the distance at which it is measured. The shape of the magnet is critical.
 
IMO, because there are varying 'grades' of magnets of each material, each with different strengths, the question has no clear answer. Maybe you are interested in the magnetic saturation point, or maximum magnetic flux density for each?
 
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Perhaps OP considered it too long to read the linked article and especially it's table. While it doesn't mention lodestone it does give relative strengths for Iron and Neodymium-Iron-Boron.
 
The K&J magnetics page contains only Nd. The Wikipedia page mentions Nd and "refrigerator magnets", which I assume are ceramic ferrite.

Anyone actually know? What is the relative magnetic strength of:

A lodestone (Fe3O4)
An iron magnet (Fe)
A Nd2Fe14B magnet

-Jeff

Thanks to those that have replied! I appreciate I'm not asking a simple question.
 
JeffEvarts said:
The K&J magnetics page contains only Nd. The Wikipedia page mentions Nd and "refrigerator magnets", which I assume are ceramic ferrite.

Anyone actually know? What is the relative magnetic strength of:

A lodestone (Fe3O4)
An iron magnet (Fe)
A Nd2Fe14B magnet

-Jeff

Thanks to those that have replied! I appreciate I'm not asking a simple question.

relative to what ??

did you not read Vanadium50's response ?
you haven't specified the factors that determine the field strength

Vanadium50 said:
The problem is that you usually need two numbers to specify the strength - the field strength and the distance at which it is measured. The shape of the magnet is critical

and I will add size/ mass of any of those magnetic materials
without the appropriate info you question is unanswerable

Dave
 

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