15:30-16:00

Hollow Microporous Nanostructures: Exquisite Construction of Prussian Blue Analogues

Crystalline coordination polymers are widely utilized due to the advantages such as flexible structure, high specific surface area as well as narrow pore-size distribution. Making crystalline coordination polymers into nanostructures is a promising way to further enhance the performance and explore new functions of them. Hollow crystalline porous coordination polymers are interesting materials because of the open microporous shells and large cavities. However, it is difficult to get hollow coordination polymer without losing microporosity by conventional ways. We have developed a facile route to prepare crystalline Prussian Blue analogues nanoparticles with hollow interiors by controlled construction and etching. Benefiting from the unique structures, hollow Prussian Blue analogues showed interesting magnetic property and high porosity. The uniform micropores and high specific surface areas made hollow Prussian Blue analogues to be good candidates for water treatment and drug delivery.

Speaker

Dr. Ming Hu, ICYS-MANA Researcher, NIMS

Chair

Dr. Kenjiro Miyano, Managing Director, ICYS, NIMS

16:00-16:30

Random Fan-Out State Induced by Site-Random Interlayer Couplings

Infinite-layer iron oxide SrFeO₂ exhibits a Néel transition to the (πππ) ordered phase at 473K^[1], and the transition temperature decreases as more Fe ions are substituted by Mn ions^[2]. In the neutron diffraction measurements on Sr(Fe_1-xMn_x)O₂ where x=0.3, it has been observed that the magnetic peaks develop at (πππ) and (ππ0) wave vectors at low temperature^[3]. However, a detail of spin ordering pattern in the low-temperature phase and a mechanism of coexisting of (πππ) and (ππ0) wave vectors have not been clarified from experimental researches. In order to understand the spin ordering pattern in the low-temperature phase of Sr(Fe_0.7Mn_0.3)O₂, we study the low-temperature properties of a classical Heisenberg model with site-random interlayer couplings on the cubic lattice^[3,4]. This model is introduced as a simplified effective model of Sr(Fe_1-xMn_x)O₂. By Monte Carlo simulation results of our model, we find the novel bulk spin structure called the “random fan-out state” which explains the simultaneous appearance of (πππ) and (ππ0) wave vectors. This magnetic structure has three feature: (i) arrangement of spins in each layer is Néel order, (ii) correlation between next-nearest layers is ferromagnetic, (iii) magnetization vector in odd-numbered and that in even-numbered layers are not parallel or antiparallel to each other, and the angle between these vectors depends on the ion concentration. Furthermore, we perform the Rietveld structural refinement and find that the neutron diffraction pattern observed in Sr(Fe_1-xMn_x)O₂ is well fitted by using the random fan-out state. Thus, we conclude that it is highly possible that the coexistence of (πππ) and (ππ0) wave vectors in Sr(Fe_1-xMn_x)O₂ is due to the random fan-out state. The collaborators are Prof. Naoki Kawashima (Univ. Tokyo), Prof. Hiroshi Kageyama (Kyoto Univ.), Dr. Cedric Tassel (Kyoto Univ.), Dr. Liis Seinberg (Kyoto Univ.), and Mr. Takafumi Yamamoto (Kyoto Univ.).

References

[1] Y. Tsujimoto et al., Nature 450, 1062 (2007).

[2] L. Seinberg et al., Inorg. Chem. 50, 3988 (2011).

[3] R. Tamura et al., Phys. Rev. B 84, 214408 (2011).

[4] R. Tamura and N. Kawashima, J. Phys.: Conf. Ser. 320, 012013 (2011).

Speaker

Dr. Ryo Tamura, ICYS-Sengen Researcher, NIMS

Chair

Dr. Kenjiro Miyano, Managing Director, ICYS, NIMS