Soft magnetic material for very low residual magnetism (low remanence)
Soft magnetic material for very low residual magnetism (low remanence)
(OP)
Does anyone know what alloys / heat treatment would be good candidates for a solenoid core that is required to have very low residual magnetism (Br), high permeability and high saturation flux density (Bm)? The form of the core will be a long thin rod. The squareness (Br/Bm) is a good indicator of residual magnetism however it is not commonly provided by manufacturers of soft magnetic alloys. I believe that some Ni-Fe alloys (which exhibit low coercive force) can achieve near zero hysteresis for bipolar DC operation if properly annealed. My goal is to find an alloy that would yield a residual magnetism of 1% or less of the saturation flux. This is to insure that when the solenoid is de-energized from a fully saturated state that there is very little residual magnetism. I suspect that the long thin form of the rod will aid in this respect as the de-magnetization factor is relatively small. Seems that some of the nickel alloys have provided this performance however I cannot locate any information to confirm the performance and annealing used.





RE: Soft magnetic material for very low residual magnetism (low remanence)
There are a ton of these alloys out there.
Depending on the frequency of you signal you can select the correct alloy.
Any of the transformer lamination alloys would work.
For low frequency high purity Fe or Fe-Si alloys will work. There are even powdered metal grades used for some of this.
At higher frequency you start using Fe-Ni alloys.
If the field will switch very fast then you need good high frequency response.
You can find hysteresis loss curves for these magnetically soft alloys.
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Plymouth Tube
RE: Soft magnetic material for very low residual magnetism (low remanence)
Long thin rod will lead to the opposite direction you desired: with a higher Br. The reason is the same as you indicated, larger L/D will have a lower demag factor. but the result is a higher Br due to less demag.
RE: Soft magnetic material for very low residual magnetism (low remanence)
MagBen - Thank you for your assistance. You are right about the demagnetizing factor, I had its effect inverted. The long thin rod will have a small demagnetization factor which will only serve to slightly reduce the residual moment. What I have come to believe is that some reasonably common alloy coupled with a special annealing process will work. I believe that similar designs that provide residual moments on the order of 1% have used Ni alloys.
In general, is there a recognized order in the value of Br/Bs for the common soft magnetic materials? For instance, if Ni alloys are always better than Co alloys I can discard consideration of the Co alloys. Finally, does low carbon steel deserve consideration as a potential solution.
RE: Soft magnetic material for very low residual magnetism (low remanence)
in terms of perm: FeNi> FeSi > pure Fe > carbon steel > FeCo/stainless steel.
Br is not an intrinsic property. you can get a linear flat hysteresis loop for a rod simply by magnetizing perpendiculr to the length, the big shape anisotropy makes the magnetization a spin rotation process, rather than domain wall movement. the same principle applies when applying a magentic field perpendicular to magnetization direction during anneal, which leads to an induced anisotropy.
RE: Soft magnetic material for very low residual magnetism (low remanence)
RE: Soft magnetic material for very low residual magnetism (low remanence)
For a rod, if you magnetize it along the transverse direction, you would probably get a linear loop, no need annealing under an external field. But I donot know why people would use the rod material this way. I cannot imagine how you are going to use rods for solenoid applicaitons with magnetization direction perpendicular to the length.
For strip or sheet products, one of my projects was to apply an external field perpendicular to magentization direction (flux flow direction) such that the loop is linear, and so i got a constant permeability at some field range. The purpose was to decrease harmonic distortion.
Magnetic anneal can be very trick. It does not work for all types of magnetic alloys. For a same alloy when it works, even applied a field at the same direction as flux flow direction, one can obtain either a square loop, or a flat loop, depending on the annelaing temperature and time.
RE: Soft magnetic material for very low residual magnetism (low remanence)
RE: Soft magnetic material for very low residual magnetism (low remanence)
seems that the op needs to be more specific about what functionality is being sought , clearly not just a materials issue
RE: Soft magnetic material for very low residual magnetism (low remanence)
I am not aware there are obvious effects of magnetic annealing on pure Fe, stainless steel. Combining cold roll percentage and annealing temperature, we can make anisotropic (more square loops) Fe-Ni and Fe-Si. You may try to anneal Fe-(50-55)Ni rod with the present of an external DC field (10-20Oe) perpedicular to length (temp needs < Curie point) to induce an anisotropy transverse to the rod. A simple while feasible way may be applying a small reverse current to demag the rod. Note it is almost no way to fully demag the rod, but since the reverse current is such small, even a reversly magnetized field can be small.
RE: Soft magnetic material for very low residual magnetism (low remanence)
RE: Soft magnetic material for very low residual magnetism (low remanence)