AsianScientist (Jan. 13, 2016) – A research group at the University of Tokyo has successfully developed the world’s smallest nanomagnet, a single-digit nanosize hard ferrite magnet composed of iron oxide, which has much greater storage capabilities than its predecessors. The magnet displays both magnetic and electrical properties and is eco-friendly and low-cost, making it suitable for mass production. The article was published in Nature.
Ferrite magnets made of iron oxide are widely used in permanent magnets, electromagnetic wave absorbing materials, magnetic fluids and particularly, magnetic recording media. There is a constantly growing need to increase the storage density of such materials. To this end, nanometer-scale magnetic particles with a large coercivity, or resistance to change in magnetic state, are needed.
However, developing such particles remains a challenge. Ferrite magnets have the chemical stability required at the nanometer scale, but since existing materials cannot maintain magnetism as particle size is reduced, there were no hard ferrite magnets with a particle size of less than ten nanometers.
Led by Professor Ohkoshi Shin-ichi from the Graduate School of Science, the University of Tokyo, the research group developed a new method to systematically synthesize epsilon-type iron oxide (ε-Fe2O3) particles of different sizes in the range of five to 40 nm. Their findings revealed that ε-Fe2O3 particles larger than 7.5 nm exhibit magnetic properties, in a phenomenon known as ferromagnetic phase transition.
Furthermore, for use in magnetic recording media such as magnetic tape and hard discs, a material should have a coercive field larger than 3 kilo oersted (kOe). The developed material exhibits a coercive field of 5 kOe at 8 nm particle size, demonstrating its effectiveness as a material for ultra-high density magnetic recording.
In addition, epsilon-type iron oxide has been shown theoretically and experimentally to exhibit not only ferromagnetic properties, but also spontaneous electric polarization—making it the smallest multiferroic ferrite particle yet.
“The ferrite magnet that we have developed may have applications as a future material for magnetic tape storage, a technology used by Google and others as a mass storage medium for archiving big data—and the focus of intense interest,” says Ohkoshi.
“Epsilon-type iron oxide has the lightest color among ferrite magnets, making it suitable for novel applications, such as in transparent magnetic paints and magnetic color toner for printers,” he adds.
The article can be found at: Ohkoshi et al. (2015) Nanometer-size Hard Magnetic Ferrite Exhibiting High Optical-transparency and Nonlinear Optical Magnetoelectric Effect.
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Source: University of Tokyo.
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