what is heisenberg exchange interaction, explain how it  used to find ferromagnetic behavior of solid?
538688
Ferromagnetism and the Curie temperature were explained by Weiss in terms of a huge internal field, the ‘molecular field’ proportional to the magnetization. No such magnetic field really exists, but it is a way of representing the effect of quantum mechanics on the Coulomb interaction.  The Weiss model can be applied to localized or delocalized electrons. Heisenberg represented the interaction of two localized spins S1 and S2 by the Hamiltonian H = -2JS1.S2. When J> 0, the exchange is ferromagnetic, leading to ferromagnetic order but when J<0, the exchange is antiferromagnetic, leading to magnetic order that depends on lattice topology.\n\nIt is not possible to discuss the mathematics here, but one can find it on the internet. For example, see:
454087
Use the formula:\n\nmagnetic moment = sqrt(n(n+2)\nwhere n = number of unpaired electrons.\n\nEg Mn has 5 d electrons, therefore, Mn2+ could have a maximum of 3 unpaired electrons. Plugging 3 into the above formula gives:\n sqrt(3(3+2) = sqrt(15) = 3.87 BM.
1009498
Dont know much but plz try this\n\nhttp://www.google.co.uk/search?hl=en&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=magnetic+particle+testing+the+testing+particles&spell=1
1096386
All normal matter is composed of particles such as protons, neutrons and electrons, and all of these have the fundamental property of quantum mechanical spin. Spin gives each one of these particles an associated magnetic field. Because of this, and the fact that the average microscopic piece of matter contains huge numbers of these particles, it would be expected that all matter would be magnetic. Even antimatter would have magnetic characteristics. However, everyday experience shows that this is not the case.\n\nWithin each atom and molecule, the spin of each of these particles is highly ordered as a result of the Pauli Exclusion Principle. However, there is no long range ordering of these spins between atoms and molecules. Without long range ordering, there is no net magnetic field because the magnetic moment of each one of the particles is cancelled by the magnetic moment of other particles.\n\nPermanent magnets are special in that long range ordering does exist. The highest degree of ordering exists within magnetic domains. These domains can be likened to microscopic neighbourhoods in which there is a strong reinforcing interaction between particles, and as a result, a great deal of order. The greater the degree of ordering within and between domains, the greater the resulting field will be.\n\nLong range ordering (and the resulting strong net magnetic field) is one of the hallmarks of a ferromagnetic material.
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Magnetic property of a material is due to the arrangement of Domains in it. If you are not of science background, simply think it as it is the arrangement of atoms of the material, which is responsible for its magnetism. If you provide a permanent magnet with electric supply, the arrangement of atoms in it will be disturbed resulting in loss or decrease in its magnetism.\nNot only the electric supply, but heating or even strong jerks can also lead to the disturbed atomic arrangement and therefore decreased or completely lost magnetism.
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The exchange of electrons between atoms, making atoms have a charge, which creates magnetism. Depending on the direction of the spin of the electrons around the nucleus, if an unequal amount of electrons spin in two different directions, there will be magnetism. \n\nMagnetism is also created by running an electric current through a particular substance, electromagnetism.\n\nAll materials have magnetism, but most are in a very minute amount.
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Magnetic flux \nweber: Wb = V s = W s/A = m^2 kg/s^2 A \n\nMagnetic flux density, magnetic induction \ntesla: T = Wb/m^2 = kg/s^2 A
268504
I'm not sure anyone really "know" but there are many teltail clues.  Not all materials are magnetic except perhaps under very powerful magnetic fluxes (MRI's?) but all atoms of materials do have one or more electrons orbiting their nuclii.  We know that electrons can be directed by magnetic flux, perhaps in a TV picture tube, etc.  Therefore, the number and arrangements of electrons of the atoms differ and some create magnetic properties (dipoles or two different poles).  If an iron bar is heated to a high temperature all the iron atoms in the bar are permitted to spin around willy-nilly.  If the bar is then cooled while exposed to a strong magnetic flux (electromagnet?) all its dipoles will align uniformly with the external flux like the needles of compasses aligned with the earth's flux.  When cool, the magnet exhibits the combined strength of all the dipoles that were previously working against each other.  We know that atoms repel each other because of their electrons (and even their nuclii must be forced together to fuse because of protons) like basketballs with ballbearings at their centers, where the skins are made of rapidly orbitting electrons.  Whereas the basketballs would repel each other in any given positions, actual atoms in iron crystals repel directionally and they which can attract or repel a free electron.  The magnet has collectively directed their combined force.  If each dipole has a North and South pole, we would expect the entire magnet to also have a North and South pole, and for like poles to repel, just as in the individual dipoles.  Hope that helps a little.
185424
It will utilise quantum mechanics. At the subatomic level, matter behaves very differently to classical mechanics that we are familiar with in everyday life. The spin property of particles is not actually the particle spinning like a top, but is a term given to their angular momentum to help explain their interaction with each other.\n\nParticles can only spin in certain allowable directions, electrons have only 2 directions, other particles can have more. The ability to be in 2 spin states at once is due to uncertainty in that the particle could be in either state until it is observed and probability functions are used to describe its state.\n\nSimilarly a particle in a quantum well (a box with walls of electric potential) will move about with its energy in a fashion that can be described by its wave function. At any measurement it will be in a certain point (although with unknown momentum) but it will vary with every measurement.\n\nThese sorts of uncertainties are what are scientists are hoping to use in quantum mechanics. Calculations will actually be performed millions of times simultaneously providing varying results, but favourable probabilities will lead to the correct answer with immeasurably small innaccurary.\n\nPotential methods will utilise the spin magnetic moments of electrons, or the position of valence (outer) or free electrons moving between pairs of ions (charged atoms) accurately positioned in a semiconductor. There is still a lot of work required.
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Hysteresis is the slight difference between how something reacts going one way compared to how it acts going the other way.\n\nA typical example is a magnet. As it magnetizes, it passes through the origin (the point at which 0 electric field intensity equals 0 magnetic field intensity). This is because the initial charge of magnetism is going into an "empty" container, so to speak.\n\nHowever, when the magnet is demagnetized (or the field is flipped to the opposite polarity), there will be a small amount of "residual" magnetism from the first charging that will tend to "fight" against the reversal. What this really means is that the reverse polarity charge does not follow the exact same path ... and does not pass through the initial origin at all.\n\nYou could look at this as filling and then emptying a glass with water - the first time you fill it, the glass started out completely dry ... which meant you could put X many molecules of water into it. Then you dump it out ... but a few molecules remain adhered to the glass surface (this would be the residual). The next time it's filled, you add as much as the first time (less the residual).\n\nWhen you empty it again, it leaves a couple of molecules attached. Not necessarily the same ones as the first time, but approximately the same amount. Hence there is now a hysteresis effect occurring when you fill/empty the glass.
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All ferromagnets, lose their magnetic properties when they are heated above their respective CURIE temperatures..\nThey simply become paramagnetic and then diamagnetic...\nWhich is why god so gracefully put all curie temperatures above human temperatures...\nIf you goto superconducting temperatures, like 10 Kelvin, they also lose their magnetic properties cos their spins cant align properly... its called NEEL temperature..\nThere is a formula for the relationship between curie temp and magnetism, but i cant remember it right now (damn im gonna flunk next weeks test)\nAnyways, you dont have to worry about the magnetism to join 2 magnets..\nAll ferromagnets exhibit magnetism when they are in the BCC structure (Body Centered Cubic) You can just heat treat it, or use gas metal arc welding, or even oxy fuel  weldings, just see that the BCC structure does not get altered and no phase transformation takes place.\n\nCheers
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Gold and silver are not ferromagnetic materials and so do not have any magnetic properties. \n\nThe following explanation is from school for science.com  \n\n"Ferromagnetic materials are strongly attracted by a magnetic force. The elements iron (Fe), nickel (Ni), cobalt (Co) and gadolinium (Gd) are such materials. \n\nThe reasons these metals are strongly attracted are because their individual atoms have a slightly higher degree of magnetism due to their configuration of electrons, their atoms readily line up in the same magnetic direction, and the magnetic domains or groups of atoms line up more readily. \n\nIron and steel\nIron is the most common element associated with being attracted to to a magnet. Steel is also a ferromagnetic material. It is an alloy or combination of iron and several other metals, giving it greater hardness than iron, as well as other specialized properties. Because of its hardness, steel retains magnetism longer than iron.\n\nPermanent magnets\nAlloys of iron, nickel, cobalt, gadolinium and certain ceramic materials can become "permanent" magnets, such that they retain their magnetism for a long time."\n\nTry looking at the website for more information. Hope that helps!
139513
Metals are attracted to magnets due to unbonded electron pairs that can be easily influenced by a magnetic field.\nFerrous metals (refering to Iron) can be easily influenced by a magnetic field, making them very magnetic.
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Good question:\n\nThere are two ways to create a magnetic field. One is to move charges or  create time dependend electric fields, that's part of the classical electrodynamics and referred to as electromagnetism.\n\nThe other one is through the "elementary magnets" in a substance. These elementary magnets are related to the spin of the subatomic particles, for example the electrons in a crystall lattice. That's what you usually call the magnetic properties, like ferro-, para-, ... magnetism.\n\nAlthough it seems that these are quite different things they are related to each other by the Einsteins theory of relativism.\n\nConsider a chain of moving electrons, each having an electric field. In the reference system of the electrons the just have the usual electric field of a resting electron. But a resting observer would see a different distance between the electrons because of the relativistic length dilation, and because of that feel a different electric field, if calculated properly this would explain electromagnetism as a relativistic correction to the electrodynamics.\n\nThe basic equation of quantum dynamics is the Schrödinger equation, which is a non relativistic equation and couldn't predict the spin. Dirac (and Klein and Gordon) made some relativistic extensions to the Schrödinger equation, and it showed up that now the extended Schrödinger equations (Dirac and Klein-Gordon equations) now contain the spin of the elementary particles.\n\nSo yes: From a phenomenological point of view there is a difference, and no, from a higher point of abstraction they are both relativistic effects and there is no difference.
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This isn't the final answer, but it is a clue:\n\nhttp://www.thesheetmetalshop.com/pdf_manual/Problem1.pdf
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Iron (like steel and certain alloys) contains atomic magnets or dipoles which can line up their 'magnetic axes' in a preferred direction.  In the magnetized state, all the magnetic axes will point in one specific direction, by which the iron filling will show polarity and hence be a magnet itself.\nWhen you heat the iron fillings, the high temperature makes the atoms to vibrate with increasing energy and this disturbs the dipoles and so the resultant magnetic axes point in their 'preferred' random directions, which keep changing due to the extra energy. If the iron fillings were magnetized before heating, all the magnetism would be lost. Magnetizing them after heating will not align the vigorously vibrating atomic magnets and rapidly changing magnetic axes.
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Iron is usually attracted to a magnet. If a bar of iron is magnetized, One end of the bar will attract one pole of the magnet, and repel the other pole of the magnet. \nCopper, nickel, and zinc are not magnetic. They neither attract or repel a magnet, and they cannot be magnetized.