Giant multiple caloric effects in charge transition ferrimagnet

Kosugi, Yoshihisa*; Goto, Matato*; Tan, Z.*; Kan, Daisuke*; Isobe, Masahiko*; Yoshii, Kenji; Mizumaki, Masaichiro*; Fujita, Asaya*; Takagi, Hidenori*; Shimakawa, Yuichi*

Scientific Reports (Internet), 11(1), p.12682_1 - 12682_8, 2021/06

https://doi.org/10.1038/s41598-021-91888-8

Caloric effects of solids provide more efficient and environment-friendly innovative refrigeration systems compared to the widely-used conventional vapor compressive cooling systems. Exploring novel caloric materials is challenging but critically important in developing future technologies. Here we discovered that the quadruple perovskite structure ferrimagnet BiCuCrO shows a large multicaloric effect at the first-order charge transition occurred around 190 K. Large latent heat and the corresponding isothermal entropy changes 28.2 J K kg can be fully utilized by applying both magnetic fields (magnetocaloric effect) and pressure (barocaloric effect). Adiabatic temperature changes reach 3.9 K for the 50 kOe magnetic field and 4.8 K for the 4.9 kbar pressure, and thus highly efficient thermal controls are achieved by multiple ways.

Local structural analysis of half-metallic ferromagnet CrO

Kodama, Katsuaki; Ikeda, Kazutaka*; Isobe, Masahiko*; Takeda, Hikaru*; Ito, Masayuki*; Ueda, Yutaka*; Shamoto, Shinichi; Otomo, Toshiya*

Journal of the Physical Society of Japan, 85(9), p.094709_1 - 094709_5, 2016/09

https://doi.org/10.7566/JPSJ.85.094709

Devil's flower resulting from a successive charge disproportionation of NaVO; Understanding of the details of the Ising spin and the competitive interactions which made the devil's flower bloom

Owada, Kenji; Fujii, Yasuhiko; Muraoka, Jiro*; Nakao, Hironori*; Murakami, Yoichi*; Noda, Yukio*; Osumi, Hiroyuki*; Ikeda, Naoshi*; Shobu, Takahisa; Isobe, Masahiko*; et al.

Hoshako, 21(2), p.87 - 96, 2008/03

http://ci.nii.ac.jp/naid/10020476047

Devil's flower has been found in a temperature-pressure phase diagram of NaVO, which shows a charge disproportionation (CD) at ambient pressure. By a complementary use of an X-ray structural analysis and a resonant X-ray diffraction, which is sensitive to CD, we have investigated the structural relationship between two ground states appeared in lower and higher pressure regions including the charge arrangements. It has been clarified that two equivalent types of charge arrangement in CD correspond to the Ising variable in NaVO. The atomic shifts are regarded as linearly coupled to the Ising spins. The results lead us to the conclusion that it is the first time that the devil's flower blooms in a charge-disproportionation system. The results also lead us to a hypothesis that the competitive interactions between a Ising spins may result from the Ising spin-phonon coupling.

Discovery of the "Devil's flower" in a charge-ordering system; Synchrotron X-ray diffraction study of NaVO

Owada, Kenji; Fujii, Yasuhiko; Nakao, Hironori*; Murakami, Yoichi*; Isobe, Masahiko*; Ueda, Yutaka*

Modern Physics Letters B, 20(5), p.199 - 214, 2006/02

https://doi.org/10.1142/S0217984906010548

We review recent synchrotron diffraction studies of NaVO. The resonant X-ray scattering performed on a monoclinically-split single domain of NaVO shows a critically enhanced contrast between V and V ions. The results has led us to the unequivocal conclusion of the charge-order pattern of low-temperature phase of NaVO below = 35 K. In spite of the possible four types of configuration of the zig-zag-type charge-order patterns in the -plane (A, A', B and B'), the stacking sequence along the -axis is determined as the AAA'A' type by comparison with model calculations. By assigning the A and A' configurations to Ising spins and , one can reasonably explain the previously discovered "devil's staircase"-type behavior with respect to the modulation of layer-stacking sequences at high pressures and low temperatures, which clearly resembles the global phase diagram theoretically predicted by the ANNNI model, called "devil's flower". This is the first case that the devil's flower appears in such a charge-ordering system, where charge-order patterns are regarded as Ising spins.

Estimation of Cs distribution and characteristics in the reactor under severe accident, 3; Chemical forms of Cs chemisorbed products

Suzuki, Eriko; Nakajima, Kunihisa; Miwa, Shuhei; Osaka, Masahiko; Hashimoto, Naoyuki*; Isobe, Shigehito*; Oka, Hiroshi*

no journal, , 

In order to evaluate the properties of chemisorbed cesium (Cs) onto the structural materials in nuclear reactors during severe accidents, temperature dependency of the chemical forms of Cs chemisorbed compounds was investigated based on the compilation of previous studies, the simulation tests of Cs chemisorption onto stainless steel, the acquisition of thermodynamic data and the thermodynamic equilibrium calculations, and the microstructure observation of chemical forms inside the oxide layer. It was revealed that the different Cs chemisorbed compounds were formed depending on the temperature conditions, such as Cs-Fe-O at 873-973 K, Cs-Fe-Si-O at 973-1273 K and Cs-Si-O at 1073-1273 K.

Distribution measurement at microlevel of Cs chemisorbed compounds onto stainless steel under LWR severe accident

Suzuki, Eriko; Ogawa, Hiroaki; Nakajima, Kunihisa; Nishioka, Shunichiro; Osaka, Masahiko; Yamashita, Shinichiro; Kurishiba, Ryoko*; Endo, Takashi*; Isobe, Shigehito*; Hashimoto, Naoyuki*

no journal, , 

To elucidate Cs chemisorption behaviour onto stainless steel under LWR severe accident condition, elemental distribution measurement at microlevel was performed by using XPS and TEM. As a result, it was found that Cs-(Fe)-Si-O compounds, which have different composition, could be distributed.

Microstructure of Cs chemisorbed stainless steel type 304

Suzuki, Eriko; Nakajima, Kunihisa; Miwa, Shuhei; Osaka, Masahiko; Hashimoto, Naoyuki*; Isobe, Shigehito*

no journal, , 

In order to improve the cesium (Cs) chemisorption model onto stainless steel (SUS), the chemical forms and distributions of Cs compounds formed inside of the SUS oxide layer at 873-1273 K were evaluated based on the microscopic observation. It was revealed that compositions of Cs compounds varies alonbg depth from the oxide layer surface on SUS, which was tested in 1073-1273 K. In addition, an amorphous phase containing Cs was observed inside of the oxide layer on the SUS tested in 873-973 K. These results suggest that the chemical reactions occurred inside of the SUS oxide layer are different from that in the nearest region of the SUS oxide layer surface.

Estimation of Cs distribution and characteristics in the reactor under severe accident; Chemical forms of Cs chemisorbed compounds

Suzuki, Eriko; Nakajima, Kunihisa; Miwa, Shuhei; Osaka, Masahiko; Hashimoto, Naoyuki*; Isobe, Shigehito*; Oka, Hiroshi*

no journal, , 

In order to evaluate the properties of chemisorbed cesium (Cs) onto the structural materials in nuclear reactors during severe accidents, temperature dependency of the chemical forms of Cs chemisorbed compounds was investigated based on the compilation of previous studies, the simulation tests of Cs chemisorption onto stainless steel, the acquisition of thermodynamic data and the thermodynamic equilibrium calculations, and the microstructure observation of chemical forms inside the oxide layer. It was revealed that the different Cs chemisorbed compounds were formed depending on the temperature conditions, such as Cs-Fe-O at 873-973 K,Cs-Fe-Si-O at 973-1273 K and Cs-Si-O at 1073-1273 K.

Local structural analysis on half metallic ferromagnet CrO

Kodama, Katsuaki; Ikeda, Kazutaka*; Takeda, Hikaru*; Isobe, Masahiko*; Ito, Masayuki*; Ueda, Yutaka*; Shamoto, Shinichi; Otomo, Toshiya*

no journal, , 

no abstracts in English