Hexagonal Ferrites: From Fridge Magnets to High Tech Uses

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New hexagonal ferrites-based tape could store the equivalent of 8 million books. Photo by Poor Angel

Magnets: Well Known and Developed Applications

Hexagonal ferrites are employed in many different sectors; we do not realize, but we use them in many objects and/or devices in our everyday lives.

Some examples include fridge magnets (both the magnet which keeps the door shut, and the one you stick on the outside), electric motors (there are about 100 different ferrite-based motors in every car) and loudspeakers (the part which generates the sound).

Another important use is data storage: many hard disks and tapes are made of hexagonal ferrites, some having very impressive storage capacity. In 2011, for example, Fujifilm produced a barium hexaferrite-based tape with a memory of 5 Tera-bites. How big is that? Pretty big: one tape could store the equivalent of 8 million books.

Hexaferrites: Innovative Applications

Although these common applications are very important, researchers are conducting experiments to improve the properties of these materials, and to find ways to use them for innovative applications.

A review paper, published in Progress in Materials Science described the latest developments for hexagonal ferrites. The review was written by Dr. Robert Pullar, from the Centre for Research in Ceramic and Composite Materials (CICECO) of the University of Aveiro (Portugal).

Multiferroic Materials

In the last year, there has been a sudden growth of interest in hexagonal ferrites because of their multiferroic properties. Multiferroics are materials which can have both magnetic and electric polarization; moreover, the magnetic properties can affect the electric ones, and vice versa, a process known as coupling.

Although there are already known multiferroic materials (i.e. bismuth ferrite BiFeO3), they only show these properties at very low temperatures (i.e. -140oC). At room temperature, they have very poor multiferroic properties and coupling. In the case of hexagonal ferrites, on the contrary, researchers observed excellent multiferroic behavior at room temperature.

Advanced multiferroic materials could be used in stealth technology. Photo by Wikicommon.

Field in Continuous Expansion

Dr. Robert Pullar explains why these latest discoveries are so important:

“Hexagonal ferrites and their multiferroic properties potentially could really revolutionize the market, as very few materials show good magnetic and electrical coupling at room temperature. Furthermore, hexaferrites are already major global commercial products, cheaply produced in great quantities, and no special processing is required to make them. Therefore, their production for multiferroic applications is definitely feasible.”

Multiferroic Applications: The Future

The use of hexaferrites in multiferroic applications has virtually limitless possibility. According to Dr. Pullar, they may be used for various technologies, such as, “highly sensitive magnetic field sensors (used in biomedicine), a new generation of smart stealth technology (used in military/aviation), improved data storage solutions for IT and computing, and tunable filters and switches for wireless communications.

Sources

Ötzgür, U., et al. Microwave ferrites, part 1: fundamental properties. Journal Materials Science: Materials in Electronics. 20(9), 789-834 (2009). Accessed May 27, 2012.

Gutfleisch O. et al. Magnetic Materials and Devices for the 21st Century: Stronger, Lighter and More Energy Efficient. Advanced Materials. 23(7), 821-842 (2011). Accessed May 27, 2012.

R.C. Pullar. Hexagonal ferrites: A review of the synthesis, properties and applications of hexaferrite ceramics. (2012). Progress in Materials Science. 57, 1191-1334 (2012). Accessed May 27, 2012.

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