There are two basic ferrite material groups: (1) Those having a permeability range from 20 to 850 µ are of the Nickel Zinc (NiZn) class (mix 43,61,67), and (2) those having permeabilities above 850 µ are usually of the Manganese Zinc (MnZn) class (Mix 31,77).
The NiZn ferrite cores exhibit high volume resistivity, moderate temperature stability and high ‘Q’ factors for the 500 KHz to 100 MHz frequency range. They are well suited for low power, high inductance resonant circuits. Their low permeability factors also make them useful for wide band transformer applications.
The MnZn ferrite cores, have permeabilities above 800 µ, have fairly low volume resistivity and moderate saturation flux density. They offer high ‘Q’ factors for the 1 KHz to 1 MHz frequency range. Cores from this group of materials are widely used for switched mode power conversion transformers operating in the 20 KHz to 100 KHz frequency range. These cores are also very useful for the attenuation of unwanted RF noise signals in the frequency range of 2 MHz to 400 MHz and above.
A Ferrite Mix Selection Guide is available HERE for aid in choosing the proper mix for your application. Available popular mixes include 31, 43, 61, 67, and 77