Register to reply

Duration of Permanent magnets

by Jonh Doe
Tags: duration, magnets, permanent
Share this thread:
Jonh Doe
#1
Feb24-04, 11:51 AM
P: 8
I am posting this here because I have not been able to find the answer anywhere else. I know some of you might find this quite dumb of me, since I have seen some quite learned scholars in this forum, and my question is pretty basic. I am aware I might not be in the right forum.

My question is : Do permanent magnets have a duration, and if they do, what is it aproximately and how is it measured?I know that the duration micht be different for each kind of magnets (neobydium, etc...). I am aware of the factors that cause a magnet to demagnetize (dont ask me if this is an english verb [?]) , as heat at the curie temperatue and hammering it to lossen the domains. So what I wish to know is, under unchanged conditions, will a permanent (it is just a name) magnet lose its properties? Or is it magnetic forever?

Thank you in advance for your answers
Phys.Org News Partner Physics news on Phys.org
New approach to form non-equilibrium structures
Nike krypton laser achieves spot in Guinness World Records
Unleashing the power of quantum dot triplets
Integral
#2
Feb24-04, 03:55 PM
Mentor
Integral's Avatar
P: 7,315
I can't answer your question directly, but can add some factors to consider. I belive that the work done by a magnet contributes to its demagnetization. Work being anything which causes fluxuation in the external magnetic fields. To extend the life of a magnet place a metal "keeper" across the poles. This essentially forms a magnetic short circiut chanelling the field into the metal and minimizing external effects thus maintaing a constant non changing environment.
FZ+
#3
Feb24-04, 05:55 PM
FZ+'s Avatar
P: 1,954
I am not sure, but I think that if nothing is done to the magnetic, its magnetism will not deteriorate. Why should it deteriorate, unless something is working to "randomise" its magnetisation?

Integral
#4
Feb24-04, 06:46 PM
Mentor
Integral's Avatar
P: 7,315
Duration of Permanent magnets

I would think that interaction with the earths field and other metallic materials will contribute to the randomization. Since there is always some fluctuations in the Earths field there will always be some work done on the magnet. Yes, slowly but inevitably. This is where a keeper helps, it forces a minimum length of field lines thus reducing external interactions.
FZ+
#5
Feb25-04, 10:16 AM
FZ+'s Avatar
P: 1,954
Since there is always some fluctuations in the Earths field there will always be some work done on the magnet.
I am being rather pedantic, but J Doe spoke of "unchanged conditions", where fluctuations in the earth's field to me count as a changing set of conditions.
Integral
#6
Feb25-04, 04:08 PM
Mentor
Integral's Avatar
P: 7,315
Ah! Of course! you are correct.

Silly me, my head is so stuck in the always changing real world that I have a hard time conceiving of an unchanging one!
turin
#7
Feb26-04, 08:44 PM
HW Helper
turin's Avatar
P: 2,327
If the magnet is in an environment above 0 K, then there are random interactions.
wasteofo2
#8
Feb27-04, 04:42 PM
wasteofo2's Avatar
P: 1,522
I know that alnico magnets are reported to demagnetize at approx. a .2-2% rate every century with only interactions with the earth's magnetic field and other random nominal interactions. If you're using the magnet however, whether in an electric guitar's pickup or to hold things to your refrigerator, it will demagnetize faster.
Jonh Doe
#9
Feb28-04, 12:58 PM
P: 8
Just to say that what I meant by Unchanged conditions was more of something in room conditions (for example, a magnet sitting on a couner... ), not some hypothetical 0 K situation inconcevable in any situation (or almost). I did not specify this because I did not think someone would interpret it in this way (showing my lact of knowledge in the feild of physic). I am asking the original question for a school project , so I am speaking of not too much changed conditions, not completely unchanged. Altough he was right that unchanged conditions is 0 K
turin
#10
Feb29-04, 07:35 PM
HW Helper
turin's Avatar
P: 2,327
John Doe,
I think you may be referring to my comment about 0 K. I wasn't assuming that you meant a 0 K environment; I was pointing out (to FZ and inegral, I suppose) that every real-world environment would have random thermal interactions. I wouldn't classify this as a "changing" environment, but an unpredictable (to some degree) one.


Register to reply

Related Discussions
Permanent magnets Atomic, Solid State, Comp. Physics 3
Permanent magnets. Advanced Physics Homework 4
Re: Permanent Magnets General Physics 4
Permanent Magnets Classical Physics 3
Permanent Magnets General Physics 1