The history of ferrite magnets marks one of the most important milestones in the development of permanent magnets. The first ferrite magnet was developed by Dr. Yogoro Kato and Dr. Takeshi Takei from Tokyo Institute of Technology in 1930.
This discovery eventually led to the founding of the TDK Corporation in 1935. These primary ceramic magnets were based on compounds with the general formula MFe2O4 where M can be a divalent metal ion such as Mn2+, Ni2+, Co2+, Cu2+ and Fe2+ and often a combination of these metal ions. The magnet was named as OP magnets at the time, which has been attributed to a double reference: “Okayama’s permanent magnet” (referring to the town where Tokyo Institute of Technology is located) and to “oxide powder magnet” as main constituent. Its magnetic properties were poor with energy product of only around 1 MGOe.
Modern ferrite magnets are M-type Ferrites produced from hexaferrite structure represented by the formula MFe12O19. The fabrication of hexaferrites started by Phillips Research Laboratories (The Netherlands) in 1952. The first ferrite magnets produced by Phillips were based on Barium hexaferrite BaFe12O19 which was found to develop a coercivity as high as 2100 Oersted (170 kA/m), then they began marketing Barium ferrite magnets under the trade name Ferroxdure.
There was a rapid increase in sales due to the material combined good magnetic properties with low cost. Phillips introduced an improve ferrite magnets based on Strontium hexaferrite SrFe12O19 in the 1960s. Energy products of up to 4 MGOe (31.8kJ/m3) were achieved and soon came to dominate the permanent magnet market. Magnetic properties of Strontium ferrite magnets have continuously improved in the last several decades by introducing Lanthanum (La) and Cobalt (Co). The history of ferrite magnets continues to be a testament to the evolution and significance of these essential materials.
