How long does the magnetism in a magnet last?

Answer 1

magnets are materials that produce a magnetic field of their own. Extreme examples of magnets are (1) "hard" or "permanent" magnets (like refrigerator magnets), which remember how they have been magnetized, and (2) "soft" or "impermanent" magnets, which lose their memory of previous magnetizations. "Soft" magnetic materials are often used in electromagnets to enhance (often by factors of hundreds or thousands) the magnetic field of a current-carrying wire that has been wrapped around the magnet; when the current increases, so does the field of the "soft" magnet, which is much larger than the field due to the current. Permanent magnets occur naturally in some rocks, particularly lodestone, but they are now more commonly manufactured. When heated a magnet's magnetism goes down and when cooled a magnet's magnetism goes up.

Materials without a permanent magnetic moment can, in the presence of magnetic fields, be attracted (paramagnetic), or repelled (diamagnetic). Liquid oxygen is paramagnetic; graphite is diamagnetic. Paramagnets tend to intensify the magnetic field in their vicinity, whereas diamagnets tend to weaken the magnetic field in their vicinity. "Soft" magnets, which are strongly attracted to magnetic fields, can be thought of as strongly paramagnetic; superconductors, which are strongly repelled by magnetic fields, can be thought of as strongly diamagnetic.

Physical origin of magnetism
Magnetism ultimately is due to the motion of electric charge. For a macroscopic object, like a wire loop, an electric current flowing through it has a magnetic moment. Far from the loop there is a magnetic field proportional in strength to its magnetic moment.

For a microscopic object, the physical picture is more complex. An electron within an atom can have orbital angular momentum and a magnetic moment proportional to that orbital angular momentum; the electron also has intrinsic angular momentum, or spin, and a magnetic moment proportional to that spin angular momentum. The orbital and spin angular momentum of an electron are comparable in magnitude, as are their magnetic moments. Far from the electron there is a magnetic field proportional in strength to its magnetic moment.

In addition, within the atomic nucleus are both neutrons and protons, and these too have orbital and spin angular momentum, and associated magnetic moments. However, the nuclear magnetic moment typically is much smaller than the electron magnetic moment, because magnetic moment is proportional to angular momentum but inversely proportional to mass. Nevertheless, it is this relatively small nuclear magnetic moment that is responsible for nuclear magnetic resonance (NMR), which is the basis for magnetic resonance imaging (MRI).

Although most atoms and molecules have a net magnetic moment at temperatures well below room temperature, at room temperature they typically have no net magnetic moment. However, they can often be magnetized. If the orbital magnetic properties dominate, the response typically will be diamagnetic; if the intrinsic magnetic properties dominate, the response typically will be paramagnetic.

Solids are collections of atoms and molecules. At room temperature most solids are either diamagnetic or paramagnetic.

Although for many purposes it is convenient to think of a magnet as having magnetic poles, it must be remembered that no isolated magnetic pole has ever been observed. As indicated above, the proper description is ultimately one due to electrical currents. For a magnet, these currents should be thought of as circulating about its atoms, and flowing without any electrical resistance. This physical picture is due to André-Marie Ampère, and these atomic currents are known as Amperian currents. For a uniformly magnetized bar magnet in the shape of a cylinder, the net effect of the atomic currents is to make the magnet behave as if there is a sheet of current flowing around the cylinder, with local flow direction normal to the cylinder axis.

Permanent magnets can be demagnetized in the following ways:

* Heating a magnet past its Curie point will destroy the long range ordering.
* Contact through stroking one magnet with another in random fashion will demagnetize the magnet being stroked, in some cases; some materials have a very high coercive field and cannot be demagnetized with other permanent magnets.
* Hammering or jarring will destroy the long range ordering within the magnet.
* A magnet being placed in a solenoid which has an alternating current being passed through it will have its long range ordering disrupted, in much the same way that direct current can cause ordering.

In an electromagnet which uses a soft iron core, ceasing the flow of current will eliminate the magnetic field. However, a slight field may remain in the core material as a result of hysteresis.

From the above one can know how long a magnet can withstand its magnetism.

Answer 2

It will last till the end of time but the intensity of its magnetism will decrease continually in a specific proportion with respect to time.
I am talking about Permanent Magnet.

In an electro magnet the story is different.
Its magnetic property lasts till current flows through its conductor coils.

Answer 3

In a permanent magnet permanent is the key word unless the magnet is violently jolted or moved through a strung magnetic field in the wrong way.

Answer 4

It is generally permanent unless it's exposed to extreme heat or high magnetic field. The magnetization of sedimentary layers magnetized as they formed by the earth's magnetic field identify magnetic pole reversals going back millions of years.

Answer 5

if it is a temporary magnet, then it is a matter of time

if it is a permanent magnet, it is as long as its magnetic domains are aligned. so if you don't touch it, then it will stay that way forever. plus, it wont work if you heat it up.

Answer 6

some magnets are permanent, some are temporary.
so it depends on if its prmanent or temperary.
permanent- always magnetized
temporary- can vary from seconds to years

Answer 7

indefinitely. but with weak magnets, a good fall can re-scramble the atoms

Answer 8

Forever, if it is at the right temperature.