TDK / Epcos T65 material Manganese Zinc is used for low frequency broadband transformers and EMI suppression from 10 to 200kHz, permeability ui varies with size and is between 4500 for small cores to 5200 with larger cores.   Commonly for wide band transformers and noise attenuation 0.5 to to 20MHz  Refer to the T65 Material Data Sheet for more information.  Can be used in most applications in place of Fair-rite 75 material.