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Suppression of f-Electron Itinerancy in CeRu2Si2 by a Strong Magnetic Field
Authors:
Y. H. Matsuda,
T. Nakamura,
J. L. Her,
S. Michimura,
T. Inami,
K. Kindo,
T. Ebihara
Abstract:
The valence state of Ce in a canonical heavy fermion compound CeRu2Si2 has been investigated by synchrotron X-ray absorption spectroscopy at 1.8 K in high magnetic fields of up to 40 T. The valence was slightly larger than for the pure trivalent state (Ce3+: f1), as expected in heavy fermion compounds, and it decreased toward the trivalent state as the magnetic field was increased. The field-induc…
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The valence state of Ce in a canonical heavy fermion compound CeRu2Si2 has been investigated by synchrotron X-ray absorption spectroscopy at 1.8 K in high magnetic fields of up to 40 T. The valence was slightly larger than for the pure trivalent state (Ce3+: f1), as expected in heavy fermion compounds, and it decreased toward the trivalent state as the magnetic field was increased. The field-induced valence reduction indicates that the itinerant character of the 4f electrons in CeRu2Si2 was suppressed by a strong magnetic field. The suppression was gradual and showed characteristic magnetic field dependence, which reflects the metamagnetism around Hm \sim 8 T. The itinerant character persisted, even at 40 T (\sim 5Hm), suggesting that the Kondo bound state is continuously broken by magnetic fields and that it should completely collapse at fields exceeding 200 T.
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Submitted 25 July, 2012; v1 submitted 4 April, 2012;
originally announced April 2012.
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Magnetic-field-induced spin-crossover transition in [Mn$^{\textrm{III}}$(taa)] studied by X-ray absorption spectroscopy
Authors:
Jim Long Her,
Yasuhiro H. Matsuda,
Motohiro Nakano,
Yasuhiro Niwa,
Yasuhiro Inada
Abstract:
The X-ray absorption near-edge structure (XANES) of Mn in a spin-crossover compound, [Mn$^{\textrm{III}}$(taa)], was studied in pulsed high magnetic fields up to 37T. By applying magnetic fields to the low-temperature low-spin (LS) state, significant changes in the spectra were observed, suggesting a magnetic-field-induced spin-crossover to the high-spin (HS) state. At low temperatures, the magnet…
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The X-ray absorption near-edge structure (XANES) of Mn in a spin-crossover compound, [Mn$^{\textrm{III}}$(taa)], was studied in pulsed high magnetic fields up to 37T. By applying magnetic fields to the low-temperature low-spin (LS) state, significant changes in the spectra were observed, suggesting a magnetic-field-induced spin-crossover to the high-spin (HS) state. At low temperatures, the magnetic field dependence of the changes in the spectra exhibited hysteresis. Furthermore, when the magnetic field was set to zero, a considerable remanent component was observed. The energy barrier of the HS $\to$ LS transition was evaluated from the temperature dependence of the decay time of the remanent signal. The energy barrier of the transition was found to be 134K, which is notably lower than that for other spin-crossover compounds reported previously. Since the fraction of the field-induced HS state was at most 30% and the thermodynamic macroscopic field-induced phase transition was expected to occur in fields higher than 55T, the observed field-induced transition at low temperatures down to 17K could be understood as a localized microscopic transition at the single-molecular level.
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Submitted 4 April, 2010;
originally announced April 2010.
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Anomalous pressure effect on the magnetic ordering in multiferroic BiMnO3
Authors:
C. C. Chou,
S. Taran,
J. L. Her,
C. P. Sun,
C. L. Huang,
H. Sakurai,
A. A. Belik,
E. Takayama-Muromachi,
H. D. Yang
Abstract:
We report the magnetic field dependent dc magnetization and the pressure-dependent (pmax ~ 16 kbar) ac susceptibilities Xp(T) on both powder and bulk multiferroic BiMnO3 samples, synthesized in different batches under high pressure. A clear ferromagnetic (FM) transition is observed at TC ~ 100 K, and increases with magnetic field. The magnetic hysteresis behavior is similar to that of a soft ferro…
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We report the magnetic field dependent dc magnetization and the pressure-dependent (pmax ~ 16 kbar) ac susceptibilities Xp(T) on both powder and bulk multiferroic BiMnO3 samples, synthesized in different batches under high pressure. A clear ferromagnetic (FM) transition is observed at TC ~ 100 K, and increases with magnetic field. The magnetic hysteresis behavior is similar to that of a soft ferromagnet. Ac susceptibility data indicate that both the FM peak and its temperature (TC) decrease simultaneously with increasing pressure. Interestingly, above a certain pressure (9 ~ 11 kbar), another peak appears at Tp ~ 93 K, which also decreases with increasing pressure, with both these peaks persisting over some intermediate pressure range (9 ~ 13 kbar). The FM peak disappears with further application of pressure; however, the second peak survives until present pressure limit (pmax ~ 16 kbar). These features are considered to originate from the complex interplay of the magnetic and orbital structure of BiMnO3 being affected by pressure.
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Submitted 10 March, 2010;
originally announced March 2010.
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Colossal Electroresistance and Colossal Magnetoresistance in Spinel Multiferroic CdCr2S4
Authors:
C. P. Sun,
C. L. Huang,
C. C. Lin,
J. L. Her,
C. J. Ho,
J. -Y. Lin,
H. Berger,
H. D. Yang
Abstract:
Colossal magnetoresistance (CMR) and electroresistance (CER) induced by the electric field in spinel multiferroic CdCr2S4 are reported. It is found that a metal-insulator transition (MIT) in CdCr2S4 is triggered by the electrical field. In magnetic fields, the resistivity of CdCr2S4 responds similarly to that of CMR manganites. Combing previous reports, these findings make CdCr2S4 the unique com…
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Colossal magnetoresistance (CMR) and electroresistance (CER) induced by the electric field in spinel multiferroic CdCr2S4 are reported. It is found that a metal-insulator transition (MIT) in CdCr2S4 is triggered by the electrical field. In magnetic fields, the resistivity of CdCr2S4 responds similarly to that of CMR manganites. Combing previous reports, these findings make CdCr2S4 the unique compound to possess all four properties of the colossal magnetocapacitive (CMC), colossal electrocapacitive (CEC), CER, and CMR. The present results open a new venue for searching new materials to show CMR by tuning electric and magnetic fields.
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Submitted 10 March, 2010; v1 submitted 3 March, 2010;
originally announced March 2010.
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High-field magnetization of a two dimensional spin frustration system Ni$_{5}$(TeO$_{3}$)$_{4}$X$_{2}$ (X = Br and Cl)
Authors:
J. L. Her,
Y. H. Matsuda,
K. Suga,
K. Kindo,
S. Takeyama,
H. Berger,
H. D. Yang
Abstract:
High-field magnetization, M($H$), on Ni$_{5}$(TeO$_{3}$)$_{4}$X$_{2}$ (X = Br and Cl) were measured by using a pulse magnet. These compounds have a two dimensional crystal structure and a distorted kagome spin frustrated system which is builded by the Ni$^{2+}$ ions ($\textbf{S}$ = 1). The Néel transition temperatures are $T_{N} \sim$ 28 and 23 K for X = Br and Cl, respectively. When…
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High-field magnetization, M($H$), on Ni$_{5}$(TeO$_{3}$)$_{4}$X$_{2}$ (X = Br and Cl) were measured by using a pulse magnet. These compounds have a two dimensional crystal structure and a distorted kagome spin frustrated system which is builded by the Ni$^{2+}$ ions ($\textbf{S}$ = 1). The Néel transition temperatures are $T_{N} \sim$ 28 and 23 K for X = Br and Cl, respectively. When $T < T_{N}$, we observed a step-like transition at $H_{c} \sim$ 11 and 10 T for X = Br and Cl, respectively. On the other hand, at $T > T_{N}$, the field-dependent magnetization curves behaved like a monotonically increasing straight line up to 55 T. The $H_{c}$ value is close to those obtained by previous spin resonance studies in which a model of spin-flop scenario was proposed to explain the field-dependent resonance spectra. Their model predicts a further transition at around 23 T, however, our observations did not show any plateau behaviors, saturation or other anomalies up to 55 T, suggesting that the further transition possibly exists at a much higher field region.
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Submitted 26 June, 2009;
originally announced June 2009.