15:30-16:00

Grain boundary effect on oxygen diffusion in Ba-based perovskite oxides

Perovskite oxides are widely used as electroceramics, electrochemical devices, catalysis and so on. In order to control these properties, it is necessary to reveal the oxygen incorporation and oxygen diffusion in perovskite oxides. In addition, the grain boundary in ceramics plays an important role in the oxygen diffusion and the surface reaction. However, that behavior strongly depends on the materials and we need to reveal the effect of grain boundaries on the oxygen diffusion and surface reaction in each material. It is well known that the oxygen tracer diffusion and high resolution secondary mass spectrometry (SIMS) are effective method for an evaluation of the oxygen diffusion and surface reaction in solid. Using this method, we can directly visualize the local oxygen diffusion around grain boundaries. In this presentation, I will present the recent study on the oxygen diffusion and the surface reaction around grain boundaries in Ba-based perovskite oxides by the means of oxygen tracer diffusion and SIMS.

Speaker

Dr. Ken Watanabe, ICYS-MANA Researcher, NIMS

Chair

Dr. Kazunori Takada, MANA PI, NIMS

16:00-16:45

Exploration for magnetoelectric multiferroics showing strong magnetoelectric coupling

Magnetoelectric multiferroics are old but emerging class of materials that combine coupled electric and magnetic dipole order. In these materials, ferroelectric and magnetic ordered states coexist or compete with each other. The interaction leads to a so-called magnetoelectric effect, which is the induction of magnetization by an electric field or electric polarization by a magnetic field. The magnetoelectric effect has attracted much interest for a long time, as the coupling between the magnetism and ferroelectricity can provide an additional degree of freedom in ‘magnetoelectric’ device design. However, there have been no applications using ME couplings developed to date, due mainly to materials limitations and the small magnitude of the magnetoelectric interaction.

In 2003, a new class of multiferroics such as TbMnO has been discovered. These systems exhibit gigantic ME effects accompanied by a magnetic phase transition into a spiral magnetic ordered phase ^[1]. In spiral magnets, inversion symmetry is broken owing to magnetic order, and some spiral-ordered structures such as a cycloidal one make the system polar. This means that a magnetic order can induce ferroelectricity. The ferroelectricity in the new class of multiferroics can be explained in terms of this scheme. Because spiral order often arises from the competition between nearest-neighbor and further-neighbor magnetic interactions, systems containing competing magnetic interactions (spin frustration) are promising candidates for multiferroics. On the basis of this strategy several new multiferroics related to spiral magnetic orders have been discovered in the past few years. In this talk, I introduce our strategy to find new multiferroics showing strong ME coupling and/or high ME performance such as room-temperature operation ^[2].

Reference

[1] T. Kimura, “Spiral magnets as magnetoelectrics, ”Annu. Rev. Mater. Res. 37, 387 (2007).

[2] T. Kimura, “Magnetoelectric hexaferrites”, Annu. Rev. Condens. Matter Phys. (to be published).

 

Speaker

Prof. Tsuyoshi Kimura, Division of Materials Physics, Graduate School of Engineering Science, Osaka University

Chair

Dr. Kazunari Yamaura, Principal Researcher, NIMS