Thinking about magnetic coercive field

[SamBam77]

I am trying to better understand some concepts in magnetism and I hope that someone here can help clarify a few questions that I have.

I am trying to interpret the meaning of the specific coercive fields of magnetic objects. For the sake of discussion, let’s use neodymium (rare-earth) magnets as an example. These magnets have a very high coercive field. Again, for the sake of discussion let’s say the magnet has a coercive field of 12,000 Oe (~955 kA/m),
http://www.translatorscafe.com/cafe...lator/ampere-per-meter-[A/m]-to-oersted-[Oe]/
This would mean that in order to remove magnetization (take it to the M = 0 line on the hysteresis curve) of the magnet one would need to apply this minimum magnetic field (H-field) strength.

Does it make sense to think about the field outside the magnet? What would the field in the air / vacuum be right outside the magnetic at this point?

If we know that,
H = (1/μ) * B
Where mu is the magnetic permeability of the material, we could find the B-field if we know the H-field (from the coercive field). Of course, this is not value inside the magnet, since there is a magnetization that needs to be accounted for. But in the vacuum surrounding the magnet, there should be a field that we can find.

In the above example, could we say that the magnetic induction field (B-field) need to zero the object’s magnetization would be,
B = μ_0 * H_c
B = (4pi E-7 N/A^2) * (955000 A/m) = about 1.2 Tesla

 

[Enthalpy]

Your conversion from A/m to T is about correct because Nb-Fe-B magnets have a permeability around 1. Other materials like AlNiCo have µr >> 1 .

Several fields are defined in permanent magnets. 955kA/m for an Nd-Fe-B is rather the field it offers for the using circuit, not the demagnetizing field which uses to be even bigger and translates to >2T.

This means that the induction needed to make or erase such a magnet can't be attained from a magnetic core and must be created without the help of permeability, by using a huge power for a short duration. The standard method is capacitor discharge, like 1m3 capacitors for 0.1dm3 magnets. In 10ms, it's loud and the cables must be hold firmly.

I suggest you to find material data sheets on manufacturers' websites for the material you want. They give magnetization curves which are rather clear.

 

[SamBam77]

In my example, I was not considering the field inside the magnetic (be it NdFeB, or whatever), but rather the air/vacuum immediately outside the magnet.

I should clarify that I am not really interested I specific case, but rather a more general understanding of what is going on. I just used NdFeB as an example because I thought using real numbers might clarify the question I was asking.

 

[SamBam77]

Can anyone else offer some insight?

 

[sardar]

The coercive field is a measure of the resistance of a material to demagnetization. It is the minimum external magnetic field required to reduce the magnetization of a material to zero. In the case of neodymium magnets, they have a high coercive field of 12,000 Oe, meaning that they are highly resistant to demagnetization. This is due to the strong alignment of their magnetic domains, which gives them a strong magnetic field.

It is important to note that the coercive field is a property of the material itself, not the external magnetic field. So while we can use the equation H = (1/μ) * B to calculate the B-field outside the magnet, this is not the same as the coercive field. The coercive field is an intrinsic property of the material, while the external magnetic field is dependent on the strength of the magnetization of the material.

To answer your question about the B-field in the air/vacuum outside the magnet, it would depend on the distance from the magnet and the strength of the magnetization. As you move further away from the magnet, the B-field will decrease. At the surface of the magnet, the B-field would be equal to the coercive field, but this would decrease as you move away from the magnet.

It is also important to note that the coercive field is not the same as the remanent magnetization, which is the permanent magnetization that remains in a material after the external magnetic field is removed. The coercive field is the external field required to remove all magnetization, while the remanent magnetization is the residual magnetization that remains after the external field is removed.

I hope this helps clarify some of your questions about the coercive field and its relationship to the B-field. Magnetism can be a complex topic, but understanding these concepts is crucial in understanding the behavior of magnetic materials.