What material works best as a CORE for a small coil at about 500 hertz?

I am building a small coil with 1000 turns of 36 gauge wire wound around it.  A 12 volt/ 500 hertz squarewave will feed the coil.   I want to receive this 500 hertz tone a few feet away using a sensitive receiver that i have.   However, i am having trouble figuring out what kind of CORE to use and where to purchase it.  I built several coils using various items such as steel, iron, and ferrite from a flyback transformer.  So far, the plain old STEEL works the best, but I keep thinking something else might work better.   I searched the internet, but it starts to get really confusing because of all the terminology like "flux density", permeability, field strength, mu, etc etc.  It must be something that does not retain magnetism when the coil is de-energized.  Any help would be appreciated !

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As L says, the core won't help your coil to broadcase. "air core" is probably best.
framistan (author)  steveastrouk4 years ago
I tried the experiment today with aircore and here are the results:
Metalcore signal level received = 3000 (signal units).
Air core signal level received = 2300 (signal units).

Air core works but not as well.
Depends on alignment though.
lemonie4 years ago
If you want to transmit 500Hz EM you probably want an air-core. Otherwise the energy is concentrated around the core and doesn't transmit. I believe.

iceng4 years ago
A 8 penny nail.
You might want to try the laminated core material from a small audio transformer. It would already be designed for use with frequencies in that range.

At any rate you have a very loosly coupled transformer if the two coils are a few feet apart. Performance will be highly dependant on the orientation of the two coils.