Abstract: A ferrite FM tuning core and a method of producing it. The ferrite tuning core is physically and electrically interchangeable with a powdered iron FM tuning core but exhibits a substantially lower temperature coefficient of permeability. The tuning core is a nickel-zinc ferrite containing, in mol percent, 65-70% ferric oxide, 25-30% nickel oxide, and 4.5-5.5% zinc oxide. In the method, the oxides forming the ferrite are pressed into a solid cylindrical body, and the body is heated at a rate of about 5.degree.-15.degree.F per minute to a maximum temperature of about 2000.degree.-2100.degree.F. Upon reaching the maximum temperature the ferrite body is immediately allowed to cool at a rate of about 1.5.degree.-2.0.degree.F per minute to a temperature below about 400.degree.F.