Ferrite Toroid Core: Magnesium-Zinc Ferrite, One-Day Grind, 1400 °C (Snoek 1948, Ex. II)

A soft ferrite ring core of magnesium-zinc ferrite: magnesia, zinc oxide and iron oxide ground for a whole day, pressed into a ring and fired at 1400 °C in oxygen. Snoek's ring had an initial permeability of 670 and a Curie point near 100 °C. Source: J. L. Snoek, US 2,452,530 (Philips, 1948), Example II. The violet iron oxide has its own blueprint (precipitated hematite calcined at 1000-1100 °C, after Nurdini et al. 2022); Snoek does not say how his was made. Picture: the patent's Fig. 4, the ring core.