What is permanent magnets: Definition and 61 Discussions

A magnet is a material or object that produces a magnetic field. This magnetic field is invisible but is responsible for the most notable property of a magnet: a force that pulls on other ferromagnetic materials, such as iron, steel, nickel, cobalt, etc. and attracts or repels other magnets.
A permanent magnet is an object made from a material that is magnetized and creates its own persistent magnetic field. An everyday example is a refrigerator magnet used to hold notes on a refrigerator door. Materials that can be magnetized, which are also the ones that are strongly attracted to a magnet, are called ferromagnetic (or ferrimagnetic). These include the elements iron, nickel and cobalt and their alloys, some alloys of rare-earth metals, and some naturally occurring minerals such as lodestone. Although ferromagnetic (and ferrimagnetic) materials are the only ones attracted to a magnet strongly enough to be commonly considered magnetic, all other substances respond weakly to a magnetic field, by one of several other types of magnetism.
Ferromagnetic materials can be divided into magnetically "soft" materials like annealed iron, which can be magnetized but do not tend to stay magnetized, and magnetically "hard" materials, which do. Permanent magnets are made from "hard" ferromagnetic materials such as alnico and ferrite that are subjected to special processing in a strong magnetic field during manufacture to align their internal microcrystalline structure, making them very hard to demagnetize. To demagnetize a saturated magnet, a certain magnetic field must be applied, and this threshold depends on coercivity of the respective material. "Hard" materials have high coercivity, whereas "soft" materials have low coercivity. The overall strength of a magnet is measured by its magnetic moment or, alternatively, the total magnetic flux it produces. The local strength of magnetism in a material is measured by its magnetization.
An electromagnet is made from a coil of wire that acts as a magnet when an electric current passes through it but stops being a magnet when the current stops. Often, the coil is wrapped around a core of "soft" ferromagnetic material such as mild steel, which greatly enhances the magnetic field produced by the coil.

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  1. S

    I Can trains use permanent magnets to be propelled?

    Can a train (e.g. like a maglev train) use a set of permanent magnets (not electromagnets) that somehow can be propelled and maintain at least a constant speed with them? Is this an example of such system...
  2. M

    Engineering Torque calculation of a motor with permanent magnets

    $$Vstator_{peak} = 120√2 *√2 = 240 V$$ $$Istator_{peak} = i_{q} (current on q axis)= 20*√2 = 28.2842 A $$ $$ω{15} = Ω_{15} * p = 2π * 15 = 94.2477 rad/s$$ $$ω{15} = Ω_{15} * ψ_{pm}$$ Hence $$ψ_{pm} = e0/ω15 = 168.3V/94.2477 rad/s => ψ_{pm} = 1.79 Wb$$ $$M = 3/2 * p * ψ_{pm} * iq $$ Hence $$ M...
  3. G

    B Permanent magnets and energy question

    Hi, I have read some threads on this but I still have some confusion. 1) I get that work has to be done to produce a permanent bar magnet (work to align the dipole moments to give a net field, say in a solenoid/electromagnet) so we can say that the magnet is a store of magnetic potential...
  4. S

    Sudden polarity reversal in opposing permanent magnets?

    Hi all, I'm working with a pair of multi-pole neodymium ring magnets (rated ~119lbF) and finding that if the opposing poles are forced together, with the magnets in alignment, that at very close range (may be a millimeter or two apart?) the two magnets will suddenly snap together as if one has...
  5. H

    Permanent magnets and "permeance"

    I have an indoor recumbent exerciser bike that uses a non-contact magnetic "clutch" for resistance. There is permanent-magnetic fulcrum assembly that pivots on a hinge. And a heavy iron flywheel that spins when pedaling. The arc moves toward/away from flywheel based on resistance setting...
  6. M

    Force between two neodymium permanent magnets

    So I was wondering how I calculate the magnetic force between two magnets. When we learned about magnets, we only covered magnetic fields and electricity (laplace's law) and how electricity can create a B-Field. But how will two B-fields (or magnets) affect each other? Is there a simple formula...
  7. Dante Meira

    B Do Permanent Magnets Bend Spacetime? Basic Thread

    Basic level thread here. If gravity "bends" the spacetime continuum, do a strong permanent magnet bend spacetime too? I'm no physicist, I'm layman, and I just don't know how this "bending" of spacetime works when a Jumbo jet is in free fall from 10 thousand meters high, pulled by Earth's...
  8. P

    The role of permanent magnets coupled with solenoids

    I have been experimenting with solenoids used to excite steel guitar strings electromagnetically. These can be found in a variety of infinite "sustainer" products such as the ebow. They generally consist of a pickup, an amplifier and a solenoid which form a simple electromagnetic feedback loop...
  9. M

    Magnetic levitation with permanent magnets

    so i am literally one step away from producing a floating skateboard powered by permanent magnets, so here's what i wanted to check, to make sure I haven't missed anything obvious vertical lift achieved by using vertical repelling fields rotational motion is controlled by counterbalancing the...
  10. S

    Calculating Magnetic Energy in Permanent Magnets

    Hi folk Is there a method to calculate the magnetic energy stored in a permanent magnet ? Thanks for help
  11. D

    Will a router motor have permanent magnets?

    Settle a bet: A reasonable sized (believe it is 2HP) router will not have any permanent magnets inside it upon tear-down. Instead, it uses an electromagnet. Correct?
  12. D

    Permanent Magnets: Exploring the Source of Energy

    First off, I am new here, so please don't tear me apart too hard if I miss or misinterpret something, I'll cotton on eventually :D As I understand it, when a permanent magnet repels an oppositely charged object, such as another oppositely charged permanent magnet, no energy is technically being...
  13. J

    Permanent magnets still an open problem

    Physicists often speak about permanent magnets as if there was a theory that explained why they exist, and this theory is often assumed to be the Ising model or something very much related to the Ising model. However, everybody knows that the Ising model has a severe issue with the artificial...
  14. Charles Link

    Permanent Magnets Described by Magnetic Surface Currents - Comments

    Charles Link submitted a new PF Insights post Permanent Magnets Explained by Magnetic Surface Currents Continue reading the Original PF Insights Post.
  15. N

    I Electron Spin vs Domain Creation in Permanent Magnets

    I am having difficulty thinking through how a ferromagnetic substance is permanently magnetized. I think I understand that when for example a sample of iron is heated above it curie temperature and then exposed to an external magnetic field , the sample will become permanently magnetized. The...
  16. Akmalidin

    Why permanent magnets are not used in Synchronous Motor?

    I am Telecommunication student but interested in motors.Especially, power generators.I was wondering why permanent magnets are not used in synchronous motor's stator or rotor? Is induction motor more efficient than permanent magnet used motor? What about in power plant generators, do they use...
  17. P

    Field Energy of Permanent Magnets vs. Magnetic Monopoles

    When two permanent magnets attract, their magnetic fields reinforce each other, whether they are stacked on their ends, in which case they are pointing the same direction, or whether they are stuck on their sides, in which case the two magnets are pointing in opposite directions. Everyone here...
  18. xareu

    Work done by permanent magnets

    I recall that the energy stored in a magnetic field is half the volume integral of the dot product of magnetic field and flux density vectors (H and B). When you place a piece of iron near a magnet, it does a work by attracting it. If H is 0 (I think there is only the magnetic moment vector M...
  19. Charles Link

    On the Pole Method of Magnetostatics and Permanent Magnets

    The pole method of magnetostatics is presented in many E&M textbooks, particularly the older ones, to do computations in magnetostatics and even to try to explain permanent magnets. An equation that arises in the pole method is B=H+4*pi*M (c.g.s. units), where H consists of contributions...
  20. F

    The force and torque between two permanent magnets?

    Hi all =) I am interested to find the forces and torques between two (diametrically magnetized) cylindrical permanent magnets (PMs) placed within a vicinity, as shown below: The NdFeB PMs placed beside one another with a distance, d. Both are rotated by independent external sources (I have...
  21. S

    Permanent magnets: do electrons attract each other?

    When reading about the quantum explanation of permanent magnets, I only read about electron spins. Sure, but are they behind that aggressive attractive force existing between opposite poles? Common sense tells me the only things that should attract each other in a metal are electrons and...
  22. D

    Permanent magnets vs Electromagnet

    I've been trying to figure this out for hours.. been studying for my final exam. Can somebody please help me? Are there any differences between the magnetic field around a permanent bar magnet and electromagnet? Any similarities?
  23. A

    Train from New York to San Francisco using permanent magnets only?

    Never mind the title. It could be New York City to Newark. The idea is thus: Permanent Magnet Rail - Train Now imagine a train running on rails, and permanent magnets arranged on the side of the train, suitably arranged so as to cause forward motion of the train? I am not familiar with...
  24. S

    Linear motor with permanent magnets. Where is the sticky point?

    Hello, recently I have found this diagram http://www.cropcircleconnector.com/images/part4-12.jpg Also seen some videos on youtube. If this really work in moving a magnet linearly, the first thing that someone may think is why not to combine this linear motor into a circle, to move a magnet...
  25. S

    Help with permanent magnets configuration as a movement source.

    please delete this post Hello, Accidentally I have noticed a strange behaviour using two different magnets, which I would like to discuss. The picture shows a disc magnet (shown also in the right to see the magnetization) with it's N facing upwards. Onto the disc magnet N side, a cylinder...
  26. B

    [ANSYS] Simulation of Permanent Magnets

    I have a project where I need to simulate the magnetic forces with ANSYS. I'm and intermediate ANSYS user but I have really only worked with APDL, and if possible I would like to do it in the GUI. So my problem is that I have only ever done structural and thermal models in ANSYS. I am...
  27. J

    Increasing total magnetic moment: permanent magnets ONLY

    This is possibly an engineering, rather than physics, question. (Ooooooooo! Busted!) John picks up a paperclip and notices that it has been (very weakly) magnetized... it attracts other paperclips, but only at ridiculously short distances. John wishes to foster this interesting...
  28. S

    Force between two permanent magnets at an angle

    Hay all, first post (ohai2u! ^_^), so hope this is in the right place. I feel really stupid for having to ask this, because I'm sure the answer is really trivial, but here we go... Ok so, imagine the scene - You have two permanent magnets on a table. Let's (for argument's sake) call these...
  29. M

    Strong motor using permanent magnets?

    Greetings all. I was wondering if I could build a low energy consuming but a powerful motor using neodymium magnets and a AC electromagnet(for switching poles N>S>N>S,etc...) The magnetic field created by the electromagnet could potentially attract a large and stronge neodymium magnet in...
  30. W

    Forces between to permanent magnets

    Forces between two permanent magnets I am new to the concept of magnetic field strength and the behavior of field lines etc, so please correct me if any of my thinking is incorrect. I want to increase the force between two permanent magnets that are at a distance apart. At the moment due to...
  31. G

    Electromagnetic Piston using a holding magnet and permanent magnets?

    Dear all - I am new here so please be gentle :smile: I have searched the site for a few days but alas still have a few questions on something i am hoping to make...so with your kind help - here we go! I am looking to make a type of electromagnetic piston, basically i want to have an...
  32. L

    Calculating the force exerted on structure by two large permanent magnets

    I am a mechanical engineering student so don't have experience in specifying magnets and or using them. So its out of my comfort zone. I currently have a U shaped structure holding two large permanent magnets apart at either end. The magnets will need to be 200x200x40 in size and the gap is...
  33. E

    Energy Loss From Permanent Magnets

    Here's a question I posted about 10 years ago as a member of the forum. No one seemed to provide a satisfactory answer then so maybe someone might have some ideas on the subject: When a permanent magnet attracts an object it does work and loses energy. When the object is pulled away is the...
  34. C

    Do Large Generators Really Use Permanent Magnets?

    I frequently teach my students about how basic generators work (motional EMFs, Faraday's Law, magnetic flux, etc.). Question: do the generators used at large power plants really use a permanent magnet as a source of the magnetic field? I was thinking that maybe an electromagnet might be...
  35. K

    Can permanent magnets be modeled as set of magnetic charges ?

    Can permanent magnets be modeled as set of "magnetic charges"? Computing the full magnetic field of a permanent magnet and what forces two permenant magnets exert on each other is obviously a field theoretic problem that requires a solve using e.g. a FEA method or simular. For two idealized...
  36. A

    Permanent magnets and magnetic energy

    Hello I am new in this forum and also my knowledge on physics is not very good. Now i am trying to understand how the permanent magnets work. We know that if we take ferromagnetic materials and by doing a specific process we can create a magnet. Then by subjecting the magnet into a high...
  37. C

    Can Magnets Be Reoriented to Confine Their Field?

    Hey everyone, I am wondering if there is a way to orient magnets so that the field is contained. Little background, i am trying to develop a device that can lift small Fe particles. I determined that a rare Earth magnet will do the trick but i need it to be switchable and...
  38. A

    Homework on permanent magnets

    Homework Statement I want to find this: C magnetic field strength of magnets C magnetic force on ferromagnetic object C force vs. distance C force vs. material thickness (shielding) Various metal objects of varrying thickness's I have a scale I have two permanent magnets...
  39. O

    Defining dimensions of a linear eddy current brakes permanent magnets

    I am designing an eddy current brake system for use in roller coaster design. I have the flux density required to reduce the speed to what i want it to be. what i need to do from that is work out the dimensions needed to obtain his flux density. the configuration is for identical magnets...
  40. B

    Calculating Distance for Hall Effect Sensor Activation

    I have what I thought should be a relatively simple problem, but a quick trip around the Google makes me wonder. It might be easier to just ask some real humans for once... I'm working with Hall Effect sensors and neodymium (NIB) magnets. I basically know the strength of my magnets, and the...
  41. N

    An interesting magnetic physics question about permanent magnets

    Imagine for a moment a steel core with no air gap, that is driven to saturation by a powerful permanent magnet. Imagine next that a coil is wrapped around some section of that core some distance away from the magnet, such that their only flux linking is through the saturated core. The magnet...
  42. N

    How to get force between two permanent magnets using ANSYS?

    Hello, I am working on a project which requires me to find the force between two permanent magnets. The configuration of the two magnets is variable, and they are of different geometries, so I thought the best way to do this would be by using ANSYS. I have never used the ANSYS...
  43. J

    Feynman QED, Permanent Magnets, and Virtual Photons

    I'm not making any statements here, only asking questions. When I take two permanent magnets and I feel the repulsive force between them, Feynman QED says it is the momentum of the virtual photons "pushing" the magnets apart? Experiments have been done, forcing some of these virtual...
  44. T

    Earth`s magnetic field and permanent magnets

    I was always fascinated by magnets and I never understood, why Earth`s magnetic field doesn`t conspicuously affect permanent magnets. Is it too weak or what?
  45. E

    Levitation with Permanent magnets

    Hi everyone, I've been trying to find info about getting an object to levitate and how strong the magnets need to be but haven't had much luck. I'm trying to build a levitating picure frame using permanent magnets rather electromagnets. The plan was to take apart a lamp and put in two ring...
  46. Z

    Maglev Train by 10 kilometer Permanent magnets

    I want know that can we build a long Permanent magnet for a Maglev way ? Please say that its possible ? (i attached one picture , with that you can understand that what is my question and what is a long Maglev way by a Permanent magnet)
  47. K

    Electromagnets and Permanent Magnets

    Hi everyone Im an engineering student currently working on a group project. Part of the project is to use a electric magnet and a permanent magnet to balance a weight on the end of a cantilever (digital scale effectively). We would then measure the current through the electromagnet to...
  48. F

    How does magnetism arise in permanent magnets?

    Hi everyone! As I understand it, magnetism can be explained by special relativity when charges are moving - length contraction in different frames of reference leads to coulomb forces between the charges in these frames. But how does magnetism in a permanent magnet arise? Are there...
  49. T

    Permanent magnets & maximum force

    What's the theoretical maximum force? At a certain distance & per kg, i guess. How would you go about calculating this?
  50. J

    Permanent Magnets: How Energy Is Stored in Magnetic Fields

    So we can think permanent magnets to be composed of large number of tiny magnetic dipoles? You can hear this in very elementary introductions. I would guess this is some kind of approximation to the spins of the atoms, or something... There is energy stored in the magnetic field, so if these...
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