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Toward highly functional devices using multi-ferroics

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Uploaded on Apr 15, 2010

[Keio Spintronics Network - Kimura's Laboratory , Osaka University]

At Osaka Universitys Graduate School of Engineering Science, the Kimura Laboratory is studying phenomena where dielectric and magnetic properties are interrelated. This research has several aims: to design and synthesize various materials; to precisely measure their structural, magnetic, and dielectric properties; to understand these phenomena; and to develop materials with highly functional characteristics.

Q. Basically, in this research we design and make materials ourselves to obtain new properties, including functional properties. We investigate physical phenomena, and in the future, wed like to put them to use in new devices.

Recently, the Kimura Lab has been focusing on materials called multiferroics. Ordinarily, electric fields and spin, or charge and magnetic fields, arent related much, so they dont influence each other much. But in multiferroics, which combine magnetic and ferroelectric ordering in one material, these properties interact, resulting in electromagnetic effects. The question of why magnetic and dielectric properties are linked in multiferroics hasnt yet been answered. But recently, its become clear that the key to this problem is the fact that spins are arranged in spirals in the multiferroics.

Q. These spiral structures are of two types, clockwise and anticlockwise. Theyre mirror images of each other. The mirror relationship is only evident when we consider the magnetic structure. Basically, such magnetic structures are not very stable, so if you apply a slight magnetic field, they collapse. Since the magnetic structures had a strong relationship with polarization, electric polarization also collapses. In such materials, their polarization changes dramatically by applying a magnetic field.

To date, multiferroics have been searched for in iron oxides. But the Kimura Lab has made a pioneering discovery in simple copper oxide: a ferroelectric property is caused by a spiral magnetic structure at very high temperatures. If multiferroics R&D advances, enabling electromagnetic effects to be controlled, itll be possible to design materials that are only magnetic when a voltage is applied. Its expected that this would lead to the development of highly functional devices.

Q. One of our aims is to find multiferroics that can actually be utilized to make useful things, though it may take 20 years. But thats not our only aim. The most interesting thing about research is that things happen that we dont predict. We work in one direction, but sometimes things happen that we dont think of beforehand. I enjoy this interesting aspect, and Id like our students to enjoy it, too. And I hope we can do research that keeps opening up new worlds.

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