ML91S MADC-F™ Mn-Zn Soft Ferrite Cores Proterial ML91S MADC-F™ Mn-Zn Soft Ferrite Cores feature low core loss at a 1MHz to 3MHz frequency range. Proterial ML91S Soft Ferrite Cores provide 900µi initial permeability at +23°C and 530mT (+23°C) or 430mT (+100°C) saturation magnetic flux density at 1000A/m. ML91S is designed for use in transformers and inductors for automotive, data center, server, and telecommunication applications.