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Journal Articles

Interface-dependent magnetotransport properties for thin Pt films on ferrimagnetic Y$$_{3}$$Fe$$_{5}$$O$$_{12}$$

Shiomi, Yuki*; Otani, Takashi*; Iguchi, Satoshi*; Sasaki, Takahiko*; Qiu, Z.*; Nakayama, Hiroyasu*; Uchida, Kenichi*; Saito, Eiji

Applied Physics Letters, 104(24), p.242406_1 - 242406_5, 2014/06

 Times Cited Count:21 Percentile:71.32(Physics, Applied)

Oral presentation

Inelastic neutron scattering study on phonon spectra in dimer-Mott insulator $$beta^{prime}$$-(BEDT-TTF)$$_2$$ICl$$_2$$

Kawamura, Seiko; Matsuura, Masato*; Iguchi, Satoshi*; Sasaki, Takahiko*; Taniguchi, Hiromi*; Kubota, Aiko*; Sato, Kazuhiko*; Inamura, Yasuhiro; Kikuchi, Tatsuya; Kawakita, Yukinobu; et al.

no journal, , 

A molecular dimer-Mott insulator $$beta^{prime}$$-(BEDT-TTF)$$_2$$ICl$$_2$$ is a candidate for a new type of ferroelectric system which shows a relaxor-like dielectric response. We performed inelastic neutron scattering measurements on this system by using a chopper specrometer, and observed phonon spectra in a wide wave vector ($$Q$$)-energy ($$E$$) region for the first time. Clear optical modes with the energies up to $$sim$$ 36 meV were observed together with an acoustic phonon dispersion. The intensity of the optical mode with the lowest energy $$E$$ = 4.2 meV increases at a zone boundary along the $$b$$* axis below $$T_{FE}$$ = 62 K, at which a glassy ferroelectricity appears, and it further increases all over the measured $$Q$$ range below the antiferromangetic transition temperature $$T_{rm N}$$ = 22 K. The results suggest that the lattice dynamics characterized by this optical phonon mode is significantly coupled with strongly correlated charge and spin degrees of freedom.

Oral presentation

Phonon modes in a molecular dimer-Mott insulator $$beta^{prime}$$-(BEDT-TTF)$$_2$$ICl$$_2$$ studied by inelastic neutron scattering

Kawamura, Seiko; Matsuura, Masato*; Iguchi, Satoshi*; Sasaki, Takahiko*; Taniguchi, Hiromi*; Kubota, Aiko*; Sato, Kazuhiko*; Inamura, Yasuhiro; Kikuchi, Tatsuya; Nakajima, Kenji

no journal, , 

Recently it has been reported that a molecular dimer-Mott insulator $$beta^{prime}$$-(BEDT-TTF)$$_2$$ICl$$_2$$ is a candidate of a new type of ferroelectric system which shows a relaxor-like dielectric response. The system exhibits a glassy ferroelectric state below $$T_c$$ = 62 K and long-range antiferromagnetic order below $$T_{rm N}$$ = 22 K. We have performed inelastic neutron scattering experiments on this system by using a chopper spectrometer AMATERAS installed at BL14 in MLF. The phonon intensity at $$sim$$18 and $$sim$$21 meV decreases with lowering temperature, while that at $$sim$$13.5 meV increases. We have already found that a period-doubled optical phonon mode at 4.2 meV is enhanced below around $$T_c$$ and then is suppressed below $$T_{rm N}$$, indicating significant relationship to both charge and spin dynamics. In sharp contrast to this low-energy mode, the intensity of the optical mode at $$sim$$18 meV decreases below $$T_c$$ to reach a constant value at a low temperature.

Oral presentation

Observation of vortex states in small superconductors with artificial pinning centres

Kitano, Kohei*; Okayasu, Satoru; Nojima, Tsutomu*; Sasaki, Takahiko*; Kokubo, Nobuhito*

no journal, , 

We try to observe a new vortex state including anti-vortex by introducing small bores or hollows in microscopic superconductors. We made direct observations of vortex states of microscopic square superconducting samples with 5 bores, located the center of the sample and four corners, by using a scanning SQUID microscope. A unique vortex alignment at low vorticity (L$$<$$5) is observed in comparison with the previous measurements on the samples with no bore. It becomes clear that the vortex alignment is determined by the distance of bores and the interaction among the vortices.

Oral presentation

Studies on phonon modes in a molecular dimer-Mott insulator $$beta^{prime}$$-(BEDT-TTF)$$_2$$ICl$$_2$$ by inelastic neutron scattering

Kawamura, Seiko; Matsuura, Masato*; Iguchi, Satoshi*; Sasaki, Takahiko*; Taniguchi, Hiromi*; Kubota, Aiko*; Sato, Kazuhiko*; Inamura, Yasuhiro; Kikuchi, Tatsuya*; Nakajima, Kenji

no journal, , 

It has been reported that in a molecular dimer-Mott insulator $$beta^{prime}$$-(BEDT-TTF)$$_2$$ICl$$_2$$ shows a relaxor-like dielectric response. The system exhibits a glassy ferroelectric state associated with charge disproportionation within the dimer, where a hole ($$S$$ = 1/2) is localized, below $$T_c$$ = 62K, and a long-range antiferromagnetic order below $$T_{rm N}$$ = 22K. For such molecule-based materials, it is expected that low-energy phonon modes are coupled with spin/charge degrees of freedom. In order to observe the phonon modes in this system, we have performed inelastic neutron scattering measurements in a wide wave-vector and energy region using a chopper spectrometer AMATERAS at J-PARC MLF. The lowest energy mode shows remarkable temperature dependence of its intensity, while any softening is not observed. The result suggests that this phonon mode reflects changes in the spin/charge dynamics.

Oral presentation

Phonon modes of $$beta^{prime}$$-(BEDT-TTF)$$_2$$ICl$$_2$$ coupled with charge and spin studied by inelastic neutron scattering

Kawamura, Seiko; Matsuura, Masato*; Iguchi, Satoshi*; Sasaki, Takahiko*; Taniguchi, Hiromi*; Kubota, Aiko*; Sato, Kazuhiko*; Inamura, Yasuhiro; Kikuchi, Tatsuya*; Nakajima, Kenji

no journal, , 

$$beta^{prime}$$-(BEDT-TTF)$$_2$$ICl$$_2$$ is an organic dimer-Mott insulator which exhibits a glassy ferroelectric state below $$T_c$$ = 62K and an antiferromagnetic order below $$T_{rm N}$$ = 22K. It is expected in such molecule-based materials that low-energy phonon modes lie in the energy region of charge and spin, and then the lattice is expected to couple with charge and spin degrees of freedom. To observe such phonon modes in this system, we have performed inelastic neutron scattering study using a chopper spectrometer AMATERAS installed at J-PARC MLF. The system shows the lowest-energy optical phonon mode at $$E$$ = 4.2 meV. which is significantly related to the charge degree of freedom. Analyzing the data more in detail, the intensity of the 4.2 meV-mode monotonically increases with lowering temperature toward $$T_c$$, becomes constant below $$T_c$$ and drastically increases below $$T_{rm N}$$. The behavior of the optical phonons at some representative $$Q$$ positions are reported.

Oral presentation

Magnetic fluctuations in strongly correlated $$f$$ electrons system URu$$_2$$Si$$_2$$ under high fields

Sakai, Hironori; Higa, Nonoka; Hattori, Taisuke; Tokunaga, Yo; Haga, Yoshinori; Kambe, Shinsaku; Goto, Takayuki*; Hirata, Michihiro*; Awaji, Satoshi*; Sasaki, Takahiko*

no journal, , 

We have performed $$^{29}$$Si nuclear magnetic resonance (NMR) experiments using single crystal of strongly correlated $$5f$$ electrons system URu$$_2$$Si$$_2$$ under high external field of about 24 T. The temperature dependence of NMR shift in the paramagnetic state varies with external fields. The temperature and field dependences of NMR shifts resembles those of magnetic susceptibility.

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