what does it mean to have a permiability less than one or more than one, i know less than one is diamagnetic and more than one is paramagnetic, but why the value 1? and whats with the negative value of permiabilities?one more thing, if water is diamagnetic that means it bends the magnetic fields around it, does this mean if i submerge a nyodenium magnet in water, no metal will be attracted to it under water? (since the magnetic field has no where to expand to, unless they expand in between the molecules)
Genius' gave a comprehensive answer; yet I' d like to add. B is called the flux density, which is number of lines per unit cross-section in a plane perpendicular to flux lines. With μ 1, B is more than that outside the material experiencing the field H. In case of water (μ 1) flux lines get very much spaced out so that B is actually less than what prevails in the field around. A Ferro-magnet in water has flux lines spaced out wide in comparison to air for example. If another piece of Ferromagnet is brought near it would move fast towards the main magnet with much more alacrity, I would imagine. It brings in the concept of 'magnetisation' and its imtensity(M) that is the magnetic moment per unit volume, since attracting and repelling magnetic 'pole pair' develop a moment. B/H 1 + 4(pi) M/H. μ 1 + 4(pi) X where X is called magnetic susceptibility. The equation could be written without H in denominator though, it is to show the dependence of μ on H also. In SI units '4(pi)' term vanishes. For water values of X are at its freezing (melting) point : -0.7019 (solid state) -0.7177 (liquid) -0.7199 (liquid) 20deg C.
Magnetic permeability is a measure of how a substance responds to a magnetic field. It may internally rearrange to reinforce the field, do nothing, or internally rearrange to oppose the field. It is often represented by the Greek letter μ: B μ H where B is the magnetic flux density in the material and H is the applied magnetic field strength. This shows the origin of the value 1. A magnetic permeability of 1 means that the material produces no change in the magnetic field. Greater than 1 means that the material is increasing the magnetic field. A small approximately linear increase is called a paramagnetic material, while a very strong increase usually showing hysteresis and variation at different field strengths is called ferromagnetism. A value less than 1 means the flux density inside the material is less than the applied field strength, which is called diamagnetism. Negative magnetic permeability is a very odd phenomenon that was purely theoretical until recently. The effect has been produce using superconducters in a strong magnetic field. Diamagnetism does reduce the effect of an imposed magnetic field but it is a small effect. Putting a magnet in water shouldn't significantly reduce its ability to attract other ferromagnetic metals.
