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Magnetoelectric Crystal Group

Magnetoelectric crystal group has been studying on crystals indicating the multiferroic phenomenon. The multiferroic, multiple ferroics in a single phase, is that of the ferroelectricity, (anti- or weak-) ferromagneticity, ferroelasticity, etc. Mainly ferroelectricity refers to a ferromagnetic and ferroelectric materials having a magnetoelectric effect expressing ferromagnetic order at the same time. Since it is possible to link electricity and magnetism, applications are expected.


Specialized field and research subject

Most multiferroic material, close to practical use, is BiFeO3. Curie temperature, Neel temperature are higher than room temperature (TC = 1103 K, TN = 643 K). The perovskite structure of BiFeO3 is dependent on the synthesis conditions. G-type antiferromagnetic spin configuration has occurred along the [001]h and [111]c orientation as a rhombohedral system or pseudo-cubic crystal system (tetragonal close to a cubic system). Due to the long-period magnetic structure of 62 nm cycle appears along the [110]h orientation of rhombohedral system at room temperature, macroscopic magnetization in bulk cyrtals will be canceled. Such long-period magnetic structure is not present in the thin film. Also originally it is antiferromagnetic, but in the thin film, it will be observed a weak ferromagnetic spin-canting (deviation from anti-parallel). BiFeO3 is expected to be applied as a ferroelectric memory device using ferroelectric, but is not easy to obtain a good ferroelectric properties since the leakage current is large for both bulk crystal and thin films. The cause of the leakage current is considering by shallow level of iron ions with multiple valencies and lattice defects of the oxygen.
Our Group aims to suppress the leakage current and improve the ferromagnetic properties. We investigated the effect of doping in the thin film in past research, and revealed that the co-doping and more elements of the buffer layer are effective in reducing the leakage current. In addition, we are investigating the substrate to deposit the thin film. So it has been attempted on a two-layer film consisted of ferromagnetic and ferroelectric films. From the viewpoint of current perspective of material science, we are promoting research on magnetoelectric crystal and multiferroic thin films.
 


"In Bi5Ti3FeO15, a large electrical magnetic (ME) coupling coefficient of 400 mV / Oe cm is obtained. Figure shows the relationship between the applied magnetization and ME coupling coefficient. Inset is MH hysteresis at room temperature. Zhao, Kimura et.al.: Sci. Rep. 4, (2014), 5255.Obtained ME coupling coefficient is 1000 times larger than past report (0.1 mV / Oe cm *) (* Bai et al .: J. Mag. Mag. Mater. 324, (2012), 2265-2270)." Image

In Bi5Ti3FeO15, a large electrical magnetic (ME) coupling coefficient of 400 mV / Oe cm is obtained. Figure shows the relationship between the applied magnetization and ME coupling coefficient. Inset is MH hysteresis at room temperature. Zhao, Kimura et.al.: Sci. Rep. 4, (2014), 5255.Obtained ME coupling coefficient is 1000 times larger than past report (0.1 mV / Oe cm *) (* Bai et al .: J. Mag. Mag. Mater. 324, (2012), 2265-2270).




Group Leader

"Hideo Kimura" Image

Hideo Kimura


Group Member

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Magnetoelectric Crystal Group
1-2-1 Sengen, Tsukuba, Ibaraki, 305-0047 JAPAN
TEL: 029-859-2437
E-Mail: KIMURA.Hideo=nims.go.jp (Please change "=" to "@")
National Institute for Materials Science (NIMS)
1-2-1 Sengen, Tsukuba, Ibaraki 305-0047, JAPAN
TEL.+81-(0)-29-859-2000
FAX.+81-(0)-29-859-2029