What is Ferromagnet: Definition and 16 Discussions

Ferromagnetism is the basic mechanism by which certain materials (such as iron) form permanent magnets, or are attracted to magnets. In physics, several different types of magnetism are distinguished. Ferromagnetism (along with the similar effect ferrimagnetism) is the strongest type and is responsible for the common phenomenon of magnetism in magnets encountered in everyday life. Substances respond weakly to magnetic fields with three other types of magnetism—paramagnetism, diamagnetism, and antiferromagnetism—but the forces are usually so weak that they can be detected only by sensitive instruments in a laboratory. An everyday example of ferromagnetism is a refrigerator magnet used to hold notes on a refrigerator door. The attraction between a magnet and ferromagnetic material is "the quality of magnetism first apparent to the ancient world, and to us today".Permanent magnets (materials that can be magnetized by an external magnetic field and remain magnetized after the external field is removed) are either ferromagnetic or ferrimagnetic, as are the materials that are noticeably attracted to them. Only a few substances are ferromagnetic. The common ones are iron, cobalt, nickel and most of their alloys, and some compounds of rare earth metals.
Ferromagnetism is very important in industry and modern technology, and is the basis for many electrical and electromechanical devices such as electromagnets, electric motors, generators, transformers, and magnetic storage such as tape recorders, and hard disks, and nondestructive testing of ferrous materials.
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 ferrimagnetic materials such as 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.

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  1. Aethermimicus

    A The relation between ferromagnets, Phi4 and non-linear sigma model

    I'm struggling to understand the relation between phi4 theory,non-linear sigma model and ferromagnets. I've read this in a paper(Phys.Rev.B14(1976)3110):'It is possible to describe the long-distance behavior of the Heisenberg ferromagnets in two different ways:the phi4 theory which corresponds...
  2. J

    I How does a ferromagnet increase the inductance of an inductor?

    Inductance according to Faraday's law depends on a changing magnetic field. The magnitude of the induced emf depends on the magnitude of change in the magnetic field per change in time. Based on that, how does adding a constant magnetic field (a ferromagnet), increase the inductance of an inductor?
  3. Rzbs

    I What makes cobalt oxide (co3o4) a magnetic material?

    We know cobalt is a magnetic material, it can attracted by magnet. Now if we want to know for example cobalt oxide (co3o4) has magnetic property or not what we should do? I mean is there a role to know bonding of cobalt with which elements results in magnetic property? or is there any online...
  4. L

    Magnetization of ferromagnetic material

    I have thought about the following ##\oint \vec{H}\cdot d\vec{l}=0\Leftrightarrow H_{int}(D-h)+H_{ext}h=0\Leftrightarrow (\frac{B}{\mu_0}-M)(D-h)+\frac{B}{\mu_0}h=0\Leftrightarrow M=\frac{D}{D-h}\frac{B}{\mu_0}## but (supposing what I have done is correct) I don't understand which value of ##B##...
  5. L

    Magnetic Surface Currents and the Interaction of Magnetic Fields with Matter

    From the graph we see that at ##H=4 kA/m,\ B=1.5T##. We have that ##M=\frac{B}{\mu_0}-H=\frac{1.5T}{\mu_0}-4kA/m## and from Ampere's Law that ##i=\frac{HL}{N}=\frac{4kA/m\cdot 0.1 m}{100}## and the current (density on the surface is) ##\sigma_{m}=M##. Does this make sense? I am having...
  6. peroAlex

    Electromagnet with two cardboard pieces

    Hello! Recently I was going through some old exams and upon encountering this problem (which seemed pretty easy) I got stuck. Exams at my university are composed of individual tasks, each having three subquestions with four plausible answers respectively. Solution sheet gives results only, so...
  7. peroAlex

    Absolute Value of Magnetization

    Hello, I'm a student of electrical engineering. This task appeared in one of the past exams. I've been using the procedure I believe should yield the correct result, however, it turns out I was wrong. Could somebody please check out where the mistake lays in my calculations? Homework Statement...
  8. L

    A Heisenberg ferromagnet -- Spontaneous symmetry breaking

    Heisenberg model of ferromagnet is defined by \hat{H}=-J \sum_{\langle i,j \rangle} \vec{S}_i \cdot \vec{S}_j where ##J>0## and summation is between nearest neighbours. Hamiltonian is perfectly rotational symmetric. However, the ground state “spontaneously” chooses a particular orientation...
  9. S

    Searching for best ferromagetic cathode for aluminum anode battery

    This is a list of ferromagnetic materials that I've found on Wikipedia's category ferromagnetic materials page. I was wondering which of these materials would make possibly great cathodes for aluminum anode in the application of creating an sulfuric solution based acid battery. The battery I...
  10. D

    A ferromagnet exposed to two fields at the same time?

    A piece of iron is placed in exterior magnetic field(+B1,"Going right"), with H = 100 Oe At the same time, there is another opposite magnetic field acting on that same iron (-B2,"Going Left") with H = 10 Oe They oppose each other, the iron is magnetized initially by B1, what happens when the...
  11. L

    Spontaneous symmetry breaking. Ferromagnet.

    I'm not sure what people meant about this. Heisenberg hamiltonian is ##O(3)## invariant. H=-J\sum_{\langle i,j \rangle} \vec{S}_i \cdot \vec{S}_j ##\langle \rangle## denotes nearest neighbors. It has ##O(3)## symmetry. If I understand well ground state is infinitely degenerate. But system...
  12. J

    Heisenberg ferromagnet and spin waves

    Hey Given an anisotropic hamiltonian \mathcal{H} = -\sum_{j,\rho} \left( J_\rho^z s_j^z s_{j+\rho}^z + \frac{J_\rho^{xy}}{2}\left( s_j^+ s_{j+\rho}^- + s_j^- s_{j+\rho}^+ \right)\right) - g\mu_B H\sum_j s_j^z Here \rho is a vector connecting the neighbouring sites. How do I show that the...
  13. P

    Is the Magnetisation of Ferromagnetic Materials Thermodynamically Reversible?

    I wonder if the process of magnetisation of ferromagnetic material is reversible in a thermodynamic sense according to the following definition of reversibility? Reversible process - let's assume that initial state of the system was a, initial state of the environment was b and final state...
  14. Y

    How to calculate the magnetic induction of ferromagnet

    1. There is a small ferromagnet,so it could product the magnet field. parameter:lenth 3mm; width 2mm ;thick 1mm magnetic susceptibility:2. 2.question If there is a position in three-dimensional space(x,y,z) . This position's magnetic induction is ?How to get it? I need...
  15. U

    Difference between a ferromagnet and a paramagnet?

    I'm doing a presentation on magnetic hysteresis, and I have a feeling one of the profs will ask me what is the difference between a ferromagnet and a paramagnet. I haven't taken my 3rd year E&M class yet, so I would just like to know what I should answer.
  16. E

    How can I produce a net translational force on a ferromagnet?

    How can I produce a net translational force on a ferromagnet?