Kawatetsu Mining Company Ltd. has developed large sized Mn-Zn ferrite single crystals mainly usea as me magnetic heads of the Video Tape Recorder, by innovating the structure of the 3 heater zone vertical Bridgman furnace and by optimizing the growth conditions. The weight of the single crystal is 28 kg, which is 110 mm in diameter and 630 mm in length, approximately 7 times as heavy as those conventionally supplied.
Distinctive features of the developed Mn-Zn ferrite single crystal are the uniformity of the composition within +/-0.5 mol%, lower included platinum particles in the crystal and elimination of cracks along with almost the full length of the crystal. In this report, the control of the variation of the composition along with the growth direction, the restriction of the dissolution of the platinum in melt and the suppression of the cracks, which had been main problems to be overcome during the development, are described.