What are the Curie and Néel temperatures, and what happens to a core if you exceed the specified Curie or Néel temperature?
The Curie temperature refers to the transition temperature above which ferromagnetic materials lose their useful magnetic properties. Ferrite materials are actually ferrimagnetic materials [a similar but distinctly different type of magnetic material], and thus this transition temperature in ferrite cores is more correctly referred to as the Néel temperature. When the Néel temperature is surpassed the core is rendered useless in the circuit.
What is the difference between ferrite cores and permanent magnets?
Ferrite cores are commonly referred to as “soft” magnetic materials, meaning that when they are not exposed to an electric current they do not exhibit magnetism. Permanent magnets are referred to as being “hard” magnetic materials, since their magnetism is inherent in their material, and they do not require an electric current to remain magnetized.
What is the difference between nickel-zinc ferrite cores and manganese-zinc ferrite cores?
Nickel-zinc [Ni-Zn] is used in applications with frequencies of 2 MHz and higher, and require low permeability. When permeability is increased in Ni-Zn cores, the Néel [similar to Curie] temperature decreases. Manganese-zinc [Mn-Zn] is used in applications where operating frequencies are up to 5 MHz and require high permeability. Mn-Zn cores offer permeability up to 20,000 while maintaining a relatively high Néel temperature.
Is it possible to machine ferrite cores?
It is possible to machine ferrite cores and it is a service that we offer to our customers. However, we discourage our customers from machining cores on their own if they are not set up with the appropriate equipment.
What is “gapping” and why are some cores “gapped” while others are not?
“Gapping” is the intentional introduction of an air gap, usually performed on the center leg of the core, to increase the saturation level of a core. Gapping also allows for tighter tolerances on the inductance level of the core.
Why are cores coated and what coatings are available?
In some cases, toroids and cores are coated to provide a smoother winding surface. However, coating such as nylon and polyester also provide a voltage breakdown guarantee up to 500 volts. Smaller cores are often coated with parylene that offers a voltage breakdown of 600 volts minimum.