Alnico Magnets

[bassnut]

I'm using alnico 5 bar magnets in a guitar pickup (coil etc.)
I have 2 barmagnets side by side with cylindrical pole pieces running perpendicular to the bars between them.
The magnets are facing each other N to N or S to S. The belief among many pickup makers is that alnico looses flux over time, that is, measurably over a few years. Is that true? I understand that a little is lost initally when the opposite poles are installed in proxomity to each other but, I'm told by my supplier that it remains stable after that.
Is that true?
There is a reason that I'm using alnico as opposed to ceramic and I'm taking care to keep the pickups separated during shippment for fear of loosing any more strength. I'm wondering just how sensitive an issue it is.

Thanks.

 

[bassnut]

I just read the "Rare Earth" thread on NdFeB. I wonder what that would be like in my aplication. I do use ceramic magnets on occasion if I want a stronger magnetic force, but there is a slight tone penality for ceramic vs alnico having nothing to do with their strength properties. I think its a flux pattern thing.
Can somebody explain to this layman what the differences in flux are between NdFeB, ceramic and alnico?
Can I get more "bang for the buck" using NdFeB?

Thanks again.

 

[UKpete]

It is true that the magnetization is stable once the magnet is installed, whatever the magnet material. It is possible to weaken them if there are high demagnetizing fields present, but that won't happen on a guitar pickup. The only other way to demagnetize is to heat the material up to it's Curie temperature i.e. extremely high.

Unlike Alnico, ferrite (i.e. ceramic) and rare earth magnets (NdFeB and SmCo) don't suffer demagnetization when they are taken out of circuit.

You will get the far more flux (for a given size magnet) from NdFeB, closely followed by SmCo. Ceramic is actually lower flux density than Alnico, it's main advantage over Alnico is it's low bulk cost and it is very difficult to demagnetize in applications where it matters e.g. an electric motor which could stall with a very high current.

Alnico is outdated really, it's only advantage is that it is capable of working to very high temperatures.

 

[radlett]

Alnico will lose almost nothing after magnetising and setting in the application.
If if you put them together or interfere beyond the intended application then they will demagnetise.
Alnico is used in safety situations where loss of flux over time needs to be zero.
Just need to design the circuit right in the first place.

john

 

[jmurphy115]

If you "condition" the AlNiCo magnet, that might help keep it a little more stabilized. Conditioning is magnetizing the magnet to saturation and then demagnetizing it by 5-15% or whatever you need. I am not sure if this will work in your situation