Can using a permalloy core in an electromagnet significantly increase its magnetic attraction?
Not necessarily.
The magnetic force F exerted by a magnet is the product of the magnetic field’s magnetic flux density gradient deltaB and the magnetic moment m; that is, F = deltaB × m.
The purpose of inserting an iron core into a solenoid coil is to magnetize the ferromagnetic material in the core using the magnetic field generated by the solenoid, thereby enhancing its magnetic moment. The magnetic moment of the solenoid itself is given by m1 = NIS, where N is the number of turns, I is the current, and S is the cross-sectional area of the coil. The magnetic moment of the iron core is the product of its volume V and the magnetic field strength M, i.e., m2 = MV. The magnetic field strength M of the ferromagnetic material is equal to the magnetic field strength H of the solenoid multiplied by the material’s relative permeability μ, which is the product of the vacuum permeability μ0 and the relative permeability ur of the ferromagnetic substance (i.e., μ = μ0 × ur). Finally, the total force F acting on the core is given by F = (m1 + m2) × ΔB = (NIS + MV) × ΔB = [NIS + μ0 × ur × H × V] × ΔB. Indeed, Permalloy has a very high relative permeability ur. If the current in the solenoid is small—meaning that the magnetic field strength H generated by the solenoid is also relatively low and has not yet reached the saturation point of Permalloy—then the attractive force will indeed increase. However, Permalloy has a relatively low saturation magnetic induction intensity; once the magnetic field generated by the solenoid reaches 7,000 A/m, the material will essentially be magnetized to saturation, at which point the attractive force will no longer increase further.
Therefore, the answer to your question is: it’s not necessarily so. When the current in the solenoid is relatively small and has not yet saturated the magnetic core, its attractive force can be increased. However, if the current is large enough to cause saturation, you should choose magnetic materials with high saturation magnetic flux density and high relative permeability.
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