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Journal Articles

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

 Times Cited Count:0 Percentile:0(Multidisciplinary Sciences)

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 BiCu$$_{3}$$Cr$$_{4}$$O$$_{12}$$ 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$$^{-1}$$ kg$$^{-1}$$ 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.

Journal Articles

Three-dimensional electronic structures and the metal-insulator transition in Ruddlesden-Popper iridates

Yamasaki, Atsushi*; Fujiwara, Hidenori*; Tachibana, Shoichi*; Iwasaki, Daisuke*; Higashino, Yuji*; Yoshimi, Chiaki*; Nakagawa, Koya*; Nakatani, Yasuhiro*; Yamagami, Kohei*; Aratani, Hidekazu*; et al.

Physical Review B, 94(11), p.115103_1 - 115103_10, 2016/11

AA2016-0587.pdf:2.55MB

 Times Cited Count:14 Percentile:64.66(Materials Science, Multidisciplinary)

In this study, we systematically investigate three-dimensional(3D) momentum-resolved electronic structures of Ruddlesden-Popper-type iridium oxides Sr$$_{n+1}$$Ir$$_{n}$$O$$_{3n+1}$$ using soft-X-ray angle-resolved photoemission spectroscopy (SX-ARPES). Our results provide direct evidence of an insulator-to-metal transition that occurs upon increasing the dimensionality of the IrO$$_{2}$$-plane structure. This transition occurs when the spin-orbit-coupled $$j_{eff}$$ = 1/2 band changes its behavior in the dispersion relation and moves across the Fermi energy. By scanning the photon energy over 350 eV, we reveal the 3D Fermi surface in SrIrO$$_{3}$$ and $$k_{z}$$-dependent oscillations of photoelectron intensity in Sr$$_{3}$$Ir$$_{2}$$O$$_{7}$$. To corroborate the physics deduced using low-energy ARPES studies, we propose to utilize SX-ARPES as a powerful complementary technique, as this method surveys more than one whole Brillouin zone and provides a panoramic view of electronic structures.

Journal Articles

Large trigonal-field effect on spin-orbit coupled states in a pyrochlore iridate

Uematsu, Daisuke*; Sagayama, Hajime*; Arima, Takahisa*; Ishikawa, Jun*; Nakatsuji, Satoru*; Takagi, Hidenori*; Yoshida, Masahiro*; Mizuki, Junichiro; Ishii, Kenji

Physical Review B, 92(9), p.094405_1 - 094405_6, 2015/09

 Times Cited Count:18 Percentile:68.15(Materials Science, Multidisciplinary)

Journal Articles

Engineering a spin-orbital magnetic insulator by tailoring superlattices

Matsuno, Jobu*; Ihara, Kota*; Yamamura, Shugen*; Wadachi, Hiroki*; Ishii, Kenji; Shankar, V.*; Kee, H.-Y.*; Takagi, Hidenori*

Physical Review Letters, 114(24), p.247209_1 - 247209_5, 2015/06

 Times Cited Count:113 Percentile:97.77(Physics, Multidisciplinary)

Journal Articles

Spin-orbit fluctuations in frustrated heavy-fermion metal LiV$$_{2}$$O$$_{4}$$

Tomiyasu, Keisuke*; Iwasa, Kazuaki*; Ueda, Hiroaki*; Niitaka, Seiji*; Takagi, Hidenori*; Kawamura, Seiko; Kikuchi, Tatsuya; Inamura, Yasuhiro; Nakajima, Kenji; Yamada, Kazuyoshi*

Physical Review Letters, 113(23), p.236402_1 - 236402_5, 2014/12

 Times Cited Count:13 Percentile:68.3(Physics, Multidisciplinary)

Spin fluctuations were studied over a wide momentum ($$hbar$$$$Q$$) and energy ($$E$$) space in the frustrated ${it d}$-electron heavy-fermion metal LiV$$_{2}$$O$$_{4}$$ by time-of-flight inelastic neutron scattering. We observed the overall ${it Q-E}$ evolutions near the characteristic ${it Q}$ = 0.6 $AA $^{-1}$$ peak and found another weak broad magnetic peak around 2.4 $AA $^{-1}$$. The data are described by a simple response function, a partially delocalized magnetic form factor, and antiferromagnetic short-range spatial correlations, indicating that heavy-fermion formation is attributable to spin-orbit fluctuations with orbital hybridization.

Journal Articles

Spin-orbit coupling induced semi-metallic state in the 1/3 hole-doped hyper-kagome Na$$_3$$Ir$$_3$$O$$_8$$

Takayama, Tomohiro*; Yaresko, A.*; Matsumoto, Akiyo*; Nuss, J.*; Ishii, Kenji; Yoshida, Masahiro*; Mizuki, Junichiro; Takagi, Hidenori*

Scientific Reports (Internet), 4, p.6818_1 - 6818_6, 2014/10

 Times Cited Count:30 Percentile:84.43(Multidisciplinary Sciences)

Journal Articles

Momentum-resolved electronic excitations in the Mott insulator Sr$$_2$$IrO$$_4$$ studied by resonant inelastic X-ray scattering

Ishii, Kenji; Jarrige, I.; Yoshida, Masahiro; Ikeuchi, Kazuhiko*; Mizuki, Junichiro; Ohashi, Kei*; Takayama, Tomohiro*; Matsuno, Jobu*; Takagi, Hidenori*

Physical Review B, 83(11), p.115121_1 - 115121_5, 2011/03

 Times Cited Count:67 Percentile:91.69(Materials Science, Multidisciplinary)

Journal Articles

Magnetic structure and local lattice distortion in giant negative thermal expansion material Mn$$_{3}$$Cu$$_{1-x}$$Ge$$_{x}$$N

Iikubo, Satoshi*; Kodama, Katsuaki; Takenaka, Koshi*; Takagi, Hidenori*; Shamoto, Shinichi

Journal of Physics; Conference Series, 251, p.012014_1 - 012014_4, 2010/12

 Times Cited Count:3 Percentile:78.5

Journal Articles

Gradual development of $$Gamma^{5g}$$ antiferromagnetic moment in the giant negative thermal expansion material Mn$$_3$$Cu$$_{1-x}$$Ge$$_x$$N ($$xsim$$ 0.5)

Kodama, Katsuaki; Iikubo, Satoshi*; Takenaka, Koshi*; Takigawa, Masashi*; Takagi, Hidenori*; Shamoto, Shinichi

Physical Review B, 81(22), p.224419_1 - 224419_8, 2010/06

 Times Cited Count:38 Percentile:81.73(Materials Science, Multidisciplinary)

Journal Articles

Anomalous metallic state in the vicinity of metal to valence-bond solid insulator transition in LiVS$$_{2}$$

Katayama, Naoyuki*; Uchida, Masaya*; Hashizume, Daisuke*; Niitaka, Seiji*; Matsuno, Jobu*; Matsumura, Daiju; Nishihata, Yasuo; Mizuki, Junichiro; Takeshita, Nao*; Gauzzi, A.*; et al.

Physical Review Letters, 103(14), p.146405_1 - 146405_4, 2009/10

 Times Cited Count:45 Percentile:86.42(Physics, Multidisciplinary)

We investigate LiVS$$_{2}$$ and LiVSe$$_{2}$$ with a triangular lattice as itinerant analogues of LiVO$$_{2}$$ known for the formation of a valence-bond solid (VBS) state out of an S = 1 frustrated magnet. LiVS$$_{2}$$, which is located at the border between a metal and a correlated insulator, shows a first order transition from a paramagnetic metal to a VBS insulator at T$$_{c}$$ $$sim$$ 305 K upon cooling. The presence of a VBS state in the close vicinity of insulator-metal transition may suggest the importance of itinerancy in the formation of a VBS state. We argue that the high temperature metallic phase of LiVS$$_{2}$$ has a pseudogap, likely originating from the VBS fluctuation. LiVSe$$_{2}$$ was found to be a paramagnetic metal down to 2 K.

Journal Articles

Local structure anomaly around Ge dopants in Mn$$_{3}$$Cu$$_{0.7}$$Ge$$_{0.3}$$N with negative thermal expansion

Matsuno, Jobu*; Takenaka, Koshi*; Takagi, Hidenori*; Matsumura, Daiju; Nishihata, Yasuo; Mizuki, Junichiro

Applied Physics Letters, 94(18), p.181904_1 - 181904_3, 2009/05

 Times Cited Count:41 Percentile:82.64(Physics, Applied)

Local structure analysis of Cu and Ge atoms in the negative thermal expansion material Mn$$_{3}$$Cu$$_{0.7}$$Ge$$_{0.3}$$N was conducted using X-ray absorption fine structure measurements. The temperature dependence of the interatomic distance was found to reflect the macroscopic negative thermal expansion both for Cu-Mn and Ge-Mn shells, although the magnitude of the relative change was much larger for Ge-Mn than Cu-Mn. An enhanced anomaly of the Debye-Waller factor was observed for the Ge-Mn shell in the temperature region of the negative expansion, indicating the presence of static local disorder around Ge impurities. These local structure anomalies strongly suggest that the local and inhomogeneous strain around Ge is essential in broadening the discontinuous volume contraction.

Journal Articles

Local lattice distortion in the giant negative thermal expansion material Mn$$_3$$Cu$$_{1-x}$$Ge$$_x$$N

Iikubo, Satoshi*; Kodama, Katsuaki; Takenaka, Koshi*; Takagi, Hidenori*; Takigawa, Masashi*; Shamoto, Shinichi

Physical Review Letters, 101(20), p.205901_1 - 205901_4, 2008/11

 Times Cited Count:149 Percentile:96.68(Physics, Multidisciplinary)

Giant negative thermal expansion is achieved in antiperovskite manganese nitrides when the sharp volume change associated with magnetic ordering is broadened by substitution. In this Letter, we address the unique role of the "magic" element, Ge, for such broadening in Mn$$_3$$Cu$$_{1-x}$$Ge$$_x$$N. We present evidence for a local lattice distortion well described by the low-temperature tetragonal (${it T$_{4}$}$) structure of Mn$$_3$$GeN for a range of $$x$$, where the overall structure remains cubic. This structural instability shows a strong correlation with the broadness of the growth of the ordered magnetic moment and, hence, is considered to trigger the broadening of the volume change.

Journal Articles

Frustrated minority spins in GeNi$$_2$$O$$_4$$

Matsuda, Masaaki; Chung, J.-H.*; Park, S.*; Sato, Taku*; Matsuno, Kenichiro*; Katori, Hiroko*; Takagi, Hidenori*; Kakurai, Kazuhisa; Kamazawa, Kazuya*; Tsunoda, Yorihiko*; et al.

Europhysics Letters, 82(3), p.37006_1 - 37006_5, 2008/05

 Times Cited Count:17 Percentile:68.61(Physics, Multidisciplinary)

Recently, two consecutive phase transitions were observed, upon cooling, in an antiferromagnetic spinel GeNi$$_2$$O$$_4$$ at $$T_{N1}=12.1$$ K and $$T_{N2}=11.4$$ K, respectively. Using unpolarized and polarized elastic neutron scattering we show that the two transitions are due to the existence of frustrated minority spins in this compound. Upon cooling, at $$T_{N1}$$ the spins on the $$<$$111$$>$$ kagom$'e$ planes order ferromagnetically in the plane and antiferromagnetically between the planes (phase I), leaving the spins on the $$<$$111$$>$$ triangular planes that separate the kagom$'e$ planes frustrated and disordered. At the lower $$T_{N2}$$, the triangular spins also order in the $$<$$111$$>$$ plane (phase II). We also present a scenario involving exchange interactions that qualitatively explains the origin of the two purely magnetic phase transitions.

Journal Articles

Magnetovolume effect in Mn$$_3$$Cu$$_{1-x}$$Ge$$_x$$N related to the magnetic structure; Neutron powder diffraction measurements

Iikubo, Satoshi; Kodama, Katsuaki; Takenaka, Koshi*; Takagi, Hidenori*; Shamoto, Shinichi

Physical Review B, 77(2), p.020409_1 - 020409_4, 2008/01

 Times Cited Count:100 Percentile:94.77(Materials Science, Multidisciplinary)

Magnetic structures in an antiperovskite system Mn$$_3$$Cu$$_{1-x}$$Ge$$_x$$N with a large magneto-volume effect above $$x$$=0.15 have been studied by neutron powder diffraction measurement. The present neutron study revealed that not only a cubic crystal structure, but also a $$Gamma^{5g}$$ antiperovskite spin structure, is a key ingredient of the large magneto-volume effect in this itinerant electron system. The large magneto-volume effect is possibly ascribed to the geometrical frustration originating from the corner-shared octahedra of the antiperovskite sturucture.

Journal Articles

Quasiparticle interference and superconducting gap in Ca$$_{2-x}$$Na$$_x$$CuO$$_2$$Cl$$_2$$

Hanaguri, Tetsuo*; Kosaka, Yuki*; Davis, J. C.*; Lupien, C.*; Yamada, Ikuya*; Azuma, Masaki*; Takano, Mikio*; Oishi, Kazuki; Ono, Masaki*; Takagi, Hidenori*

Nature Physics, 3(12), p.865 - 871, 2007/12

 Times Cited Count:134 Percentile:95.94(Physics, Multidisciplinary)

Journal Articles

Low-energy spectroscopic mapping studies in optimally-doped Ca$$_{2-x}$$Na$$_x$$CuO$$_2$$Cl$$_2$$

Hanaguri, Tetsuo*; Kosaka, Yuki*; Davis, J. C.*; Lupien, C.*; Yamada, Ikuya*; Azuma, Masaki*; Takano, Mikio*; Oishi, Kazuki; Takagi, Hidenori*

Physica C, 460-462, p.954 - 955, 2007/09

 Times Cited Count:1 Percentile:7.1(Physics, Applied)

We performed high-resolution scanning tunneling microscopy/spectroscopy on an optimally-doped Ca$$_{2-x}$$Na$$_x$$CuO$$_2$$Cl$$_2$$ crystal. The so-called checkerboard local-density-of-state modulation manifests in the spectroscopic map of the optimally-doped sample. In addition, spatially-inhomogeneous energy gap is observed. The gap tends to be buried at elevated temperatures and correlates with the checkerboard modulation. These results suggest that the gap is related to superconductivity which coexists with the checkerboard modulation.

Journal Articles

Spiral spin structure in the Heisenberg pyrochlore magnet CdCr$$_2$$O$$_4$$

Matsuda, Masaaki; Takeda, Masayasu; Nakamura, Mitsutaka; Kakurai, Kazuhisa; Osawa, Akira*; Leli$`e$vre-Berna, E.*; Chung, J.-H.*; Ueda, Hiroaki*; Takagi, Hidenori*; Lee, S.-H.*

Physical Review B, 75(10), p.104415_1 - 104415_6, 2007/03

 Times Cited Count:41 Percentile:82.49(Materials Science, Multidisciplinary)

A frustrated spinel CdCr$$_2$$O$$_4$$ undergoes a three-dimensional spin-Peierls transition at $$T_N$$ = 7.8 K from a cubic paramagnetic to a tetragonal N$'e$el state. The N$'e$el state has a spiral magnetic structure with a characteristic wave vector of $$(0,delta,1)$$ when the $$c$$ axis elongated. Here we report our spherical neutron polarimetry experiments to investigate the spiral spin structure in detail. Our results indicate that the spins lie in the $$ac$$ plane perpendicular to the direction of the spiral modulation. We also found that the spiral structure in the $$ac$$ plane is elliptical with the $$c$$-component larger by $$sim$$24% than the $$a$$-component, suggesting a strong coupling between the magnetic structure and structural distortion. Unpolarized neutron diffraction under an external magnetic field has also been performed. The magnetic field dependence suggests existence of magnetic anisotropy in the N$'e$el state, which is consistent with our previous inelastic studies.

Journal Articles

Statics and dynamics of incommensurate spin order in a geometrically frustrated antiferromagnet CdCr$$_2$$O$$_4$$

Chung, J.-H.*; Matsuda, Masaaki; Lee, S.-H.*; Kakurai, Kazuhisa; Ueda, Hiroaki*; Sato, Taku*; Takagi, Hidenori*; Hong, K.-P.*; Park, S.*

Physical Review Letters, 95(24), p.247204_1 - 247204_4, 2005/12

 Times Cited Count:133 Percentile:95.33(Physics, Multidisciplinary)

no abstracts in English

Journal Articles

Single-crystal growth of transition metal oxides at high pressures of several GPa

Azuma, Masaki*; Saito, Takashi*; Ishiwata, Shintaro*; Yoshida, Hirofumi*; Takano, Mikio*; Kosaka, Yuki*; Takagi, Hidenori*; Utsumi, Wataru

Journal of Physics; Condensed Matter, 14(44), p.11321 - 11324, 2002/11

 Times Cited Count:7 Percentile:39.68(Physics, Condensed Matter)

no abstracts in English

Oral presentation

Detailed magnetic structure of a frustrated spinel CdCr$$_2$$O$$_4$$ studied by polarized neutron techniques

Matsuda, Masaaki; Osawa, Akira*; Takeda, Masayasu; Kakurai, Kazuhisa; Chung, J.-H.*; Lee, S.-H.*; Ueda, Hiroaki*; Takagi, Hidenori*

no journal, , 

CdCr$$_2$$O$$_4$$ has the spinel structure, in which geometrical frustration exists between the Cr$$^{3+}$$ moments located at the corners of the tetrahedron. It shows an incommensurate antiferromagnetic ordering below $$Trm_N$$=7.8K with a characteristic wave vector of $$Q=(0, delta, 1)$$ ($$deltasim0.09$$). We first performed a 1D polarized neutron analysis and determined that the Cr$$^{3+}$$ moments has a planer anisotropy in the $$ac$$ plane, indicating that the magnetic structure is spiral. Finally, the 3D polarized neutron analysis using a CRYOPAD on TAS-1 at JRR-3 determined that the magnetic structure is elliptical spiral in the $$ac$$ plane with ellipsoid slightly elongated along the $$c$$ axis. The origin of the structure will be discussed.

38 (Records 1-20 displayed on this page)