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We have carried out hard x-ray photoemission spectroscopy (HAXPES) of Yb

The dynamic conductivity and permittivity spectra of the intermediate-valence compound YbB12 are measured in the frequency range (6–104) cm−1 (quantum energy 0.75 meV-1.24 eV) at temperatures of 5–300 K. Analysis of the spectral singularities associated with the response of free charge carriers has made it possible for the first time to determine the temperature dependences of their microscopic parameters, viz., concentration, effective mass, relaxation frequency and time, mobility, and plasma frequency. It is shown that the relaxation frequency decreases upon cooling from 300 K to the coherence temperature T * = 70 K for YbB12, which is mainly associated with the phonon mechanism of scattering of charge carriers. For cooling below the coherence temperature T * = 70 K, the temperature dependence of the relaxation frequency for charge carriers of the Fermi-liquid type is found to be γ ∼ γ0 + T 2, while their effective mass and relaxation time increase, respectively, to m *(20 K) = 34m 0 (m 0 is the free electron mass) and τ(20 K) = 4 × 10−13 s, indicating the establishment of coherent scattering of carriers from localized magnetic moments of the f centers. At a temperature of T = 5 K, the conductivity spectrum contains an absorption line at a frequency of 22 cm−1 (2.7 meV); the origin of this line can be associated with the exciton-polaron bound state. Since such a state was observed earlier in other intermediate-valence semiconductors (such as SmB6, TmSe1−x Te, and (Sm, Y)S), it is probably typical of this class of compounds.

Recent studies suggest that an exemplary Kondo insulator SmB6 belongs to a new class of topological insulators (TIs), in which non-trivial spin-polarized metallic states emerge on surface upon the formation of Kondo hybridization gap in the bulk. Remarkably, the bulk resistivity reaches more than 20 Ohm cm at 4 K, making SmB6 a candidate for a so-called bulk-insulating TI. We here investigate optical-pulse responses of SmB6 by pump-and-probe photoemission spectroscopy. Surface photovoltage effect is observed below ~90 K. This indicates that an optically-active band bending region develops beneath the novel metallic surface upon the bulk-gap evolution. The photovoltaic effect persists for >200 microsec, which is long enough to be detected by electronics devices, and could be utilized for optical gating of the novel metallic surface.

We present the measured resistivity, Hall coefficient, and magnetization for three kinds of Bi 2 Sr 2 CaCu 2 O 8+∂ ceramics subjected to various heat treatments. The Hall effect shows that in this system the carriers have hole-like characteristics. The hole density varies according to the heat treatment; the hole density increases and T c decreases as a result of oxidation. In spite of the atmosphere in which heat treatments were performed, the flux pinning density is increased by quenching. The Hall mobility is independent of the heat treatment of Bi 2 Sr 2 CaCu 2 O 8+∂ . This result indicates that oxygen atoms enter and leave sites on planes other than the CuO 2 planes in Bi 2 Sr 2 CaCu 2 O 8+∂ .

The incubation (transit) time of the perpendicular magnetic tunnel junction (MTJ) is found shorter (longer) than the in-plane MTJ. By making use of the incubation time, a new concept is proposed for MTJ/CMOS hybrid circuits that operate as fast as CMOS circuits without operation power overhead and with negligible MTJ switching error. A nonvolatile latch based on the concept is fabricated in 90nm technology to demonstrate 600MHz stable operation.

We report on X-ray photoemission (XPS), Bremsstrahlung isochromat (BIS) and 4 f resonant ultraviolet photoemission (4 f RPES or UPS) spectroscopy of Ce(Pd 1- x Cu x ) 3 (0≤ x ≤0.133). With increasing x , the 4 f 1 BIS peak clearly observable in CePd 3 is strongly depressed, the 4 f 2 BIS peak is found to shift to lower energies and the intensity of the 3 d 9 4 f 0 component of the Ce 3d core XPS is found to become weaker. These experimental results are discussed in comparison with the spectra calculated by using the impurity Anderson model. It is found that lowering of the 4 f level energy e f along with reduction of the 4 f hybridization strength V with x can qualitatively reproduce the experimental result. It is also strongly suggested that the 4 f -4 f Coulomb energies are different for the 4 f BIS and 3 d XPS final states.

We present the measured resistivity, Hall coefficient, and magnetization in three kinds of Bi2Sr2CaCu2O8+δ ceramics subjected to various heat treatments. The Hall effect shows that the carriers have the hole characteristic in this system. The hole number varies according to the heat treament. It increases and Tc decreases as a result of oxidation. In spite of the atmosphere of the heat treatment, the density of the flux pinning is increased by quenching. The Hall mobility is independent of the heat treatments for Bi2Sr2CaCu2O8+δ This result indicates that oxygens enter and leave sites on a plain other than the CuO2 plain in Bi2Sr2CaCu2O8+δ.

We have measured the magnetoresistance and de Haas-van Alphen (dHvA) effect in UB 12 . Shown by the result of magnetoresistance, this material is a compensated metal, and possesses an open orbit along the direction. The detected dHvA branches are roughly explained by the recent band calculation performed by Harima et al . The cyclotron mass is in the range of 0.6 m 0 to 6 m 0 .

The magnetic susceptibility and electrical resistivity in the metal-insulator (MI) transition of a mixed-valent Ti-oxide system, Y1-x CaxRTiO3, is investigated as a function of pressure. This system exhibits obviously the temperatureinduced MI transition at x=0. 3-0. 4. At the low temperature metallic phase, susceptibility, X (T), is strongly suppressed with pressure. On the other hand, in the high temperature semiconductiong phase X (T) obeying the Curie-Weiss law is not affected strongly with pressure. The coefficient of the T2-term in resistivity, A, and the residual resistivity, ρ (0), are decreases rapidly with pressure. At x=0. 375 and 0. 39, we recognize the relation of A∝X (10 K) 2 at the low temperature metallic state.

The metal-insulator transition in the Y 1− x Ca x TiO 3 alloy system occurs about x = 0.35. Various physical property measurements suggest that this MI transition cannot be understood as a simple change in the carrier number in the Hubbard band. In this paper, detailed magnetic property and electrical resistivity behaviours around MI transition are discussed.

The high field magnetization measurements in Lu1−xYbxB12 have been performed. In the dilute Yb region (0

The paramagnetic Meissner effect (PME) in the field cooled susceptibility has been observed in superconducting single crystals of Ba_{1-x}K_xBiO_3 using magnetometers of Quantum-Design Co.. The PME is similar to that observed in cuprates and Nb superconductors. For the Ba_{0.63}K_{0.37}BiO_3 crystal, the PME is observed in cooling process under the field up to 750 Oe. The PME was not found in the virgin-charged superconducting magnet. The PME is found in a superconductor with trapped flux and may arise from a remnant field, a temperature inhomogeneity near T_c, and a potassium-concentration inhomogeneity., Comment: 4 pages, 4 figures

We have measured the electrical resistance of the metallic dense Kondo compound CePdSn and the semiconducting dense Kondo compound YbB12 under hydrostatic pressure up to 80 kbar. The pressure dependence of the resistance and its implications for the pressure dependence of the gap energy is discussed.

The acoustic de Haas-van Alphen effects of CeCu 2 , YCu 2 and UB 12 have been observed by the sound velocity measurements. The angular variation of the frequencies and the mass enhancement effect are determined.

The time-resolved switching characteristics of 100×200 nm2 size CoFeB/MgO/CoFeB-based magnetic tunnel junction (MTJ) are investigated by using the 20 GHz sampling measurement technique. We focused on the physical quantities of the time-resolved characteristics such as incubation time t A, transit time t B, and the standard deviations σV's of the period of the switching waveform. Furthermore, the dependencies of t A and t B on the applied pulse waveforms are analyzed. We found t A exponentially decreases as the applied voltage to MTJ increases, while t B remains less than two nano seconds regardless of the applied voltage. Furthermore, it is observed that the standard deviations of the waveform during t A is larger than that of the other periods. Finally, we discuss the switching characteristics with proposed toy model based on spin transfer torque (STT) phenomena.

A novel nonvolatile static random access memory cell is proposed that consists of four transistors and two spin-transfer-torque magnetic tunnel junctions (STT-MTJs). In the case of the NFET driver cell, the free layers of the magnetic tunnel junctions are connected to the transistors' sources and drains to make the cell read-disturb free. The static power is totally eliminated as the power line is shut down during data hold. The static noise margin of the cell is calculated based on the experimental data on MTJ switching that is enhanced from the resistive load SRAM cell due to the MTJ's switching operation. The cell size is estimated to become smaller than the 6-transistor SRAM cell when it is designed at 45 nm node and beyond owing to the MTJ's area shrink as well as the thinning of its tunnel dielectrics (MgO).

In this paper, we have described the complementary metal–oxide–semiconductor (CMOS)/magnetic tunnel junction (MTJ) integrated process technology; MTJs were fabricated on via metal with surface roughness of 0.3 nm with 0.14 µm CMOS process and 60 ×180 nm2 MTJ process. It is shown that by this process technology, the fabricated MTJ on CMOS logic circuit plane achieves a large change in a resistance of 3.63 kΩ (anti-parallel) with the TMR ratio of 138% at room temperature, which is large enough for a sensing scheme of standard CMOS logic. Furthermore, we have successfully demonstrated the DC and AC operation of this MTJ with write transistors. As the results, our MTJ achieves high enough write/read performance with transistors for realizing MTJ-based logic circuits.

NMR experiments of51V are reported for a perovskite oxide CaVO3−y, whose electronic and magnetic properties are recently found to depend strongly on oxygen stoichiometry. A sharp free decay signal has been observed for a powdered sample of CaVO3.0 with a metallic Knight shift of K= 0.17 ± 0.02% and a Korringa value (T1T)−1 = 3.2 ± 0.5 (sK)−1 which confirms the material is a simple Pauli paramagnet without any appreciable importance of electron-electron correlation.

From the magnetic susceptibility and specific heat measurements, it is found that UB 12 , UIr 3 B 2 and UOs 3 B 2 have no magnetic order down to 1.7 K. The observed specific heat coefficient γ is 20, 39 and 80 mJ/mol K 3 for UB 12 , UOs 3 B 2 and UIr 3 B 2 , respectively. Mass enhancement factor for UIr 3 B 2 is about 5.5.

Magnetic susceptibility and lattice parameter measurements indicate that Yb valence in Lu1−xYbxB12 is independent of x and about 2.9–3.0. Resistivity and Hall constant measurements reveal that this alloy system changes from a Kondo-like state to the SmB6-type mixed valence state with increasing x.

High field magnetization and magnetoresistance of YbB 12 are investigated up to 550 kOe at low temperatures with special interest in the semiconductive band gap energy under the field. Very large negative magnetoresistance is found and the system is perfectly metallic around 500 kOe with anomalous increase in the magnetization. The experimental results are explained by introducing the model that the band gap produced by the mixing of the f- and conduction electrons is destroyed by applying the field and the released f-electron gives an anomalous magnetization. The g J -value is estimated as 1.9 for the f-level and this means that \(\varGamma_{8}\) may be most favourable for the responsible f-electron at the Fermi energy.

Results of our theoretical and experimental studies on the anomalous Kondo ferromagnet CeRh3B2 based on the f0 (lz = 0) band and the d0 screening of the 4f hole are shown. Gap formation in the unique compounds YbB12 and Ce(Pd1−xCux)3 is described by comparing with SmB6. Gap creation on the Kondo lattice is thereby established. Finally, a dense Kondo state in samarium compounds is shown in our recent experiments compared with that in cerium compounds.

The magnetic susceptibility, electrical resistivity, Hall effect, NMR, XPS and specific heat measurements indicate that (1) YbB12 is a mixed valence compound with the valence of + 2.9, (2) as the temperature decreases χ goes through a pronounced peak at 75 K and then decreases rapidly to a constant value after subtraction of impurity effect, (3) the transport properties are very similar to those of SmB6, (4) 1/T1 obtained from 11B NMR shows a temperature dependence of activation type, (5) the magnetic specific heat is of Schottky type. These results suggest that YbB12 is a new mixed valence compound accompanied with the formation of an energy gap. Some of the experimental results are analysed by the model used in SmB6.

The transport and specific heat measurements have indicated that (1) Sm 1− y Yb y B 6 shows Kondo effect in the low concentration range of Sm, (2) the ground state of the crystal field split J = 5 2 level of the Sm ion is a quartet Γ 8 , (3) Tm 1/2 Yb 1/2 B 6 also shows Kondo effect.

The compound CePdSn is found to be an antiferromagnet with a Neel poin of 7 K. Experimental results on the alloy system Ce ( Ni 1− x Pd x ) Sn revealed that the transport properties change from a semiconducting-like Kondo state to a metallic one with increase in x . YbNiSn is a new Kondo compound with a small ferromagnetic moment below 5.5 K.

Specific heat measurements of YbB 12 have revealed that the band gap is formed on the Kondo lattice originated from the Γ 8 ground state. Increase of C / T of Yb x Lu 1− x B 12 in the low temperature region takes place in the concentration range larger than x ≈ 1 2 and its origin also is from 4f-band gap formation.

Single phase TmB12, YbB12 and LuB12 were successfully obtained by the arc-melting and floating zone methods. The XPS measurements of these compounds have indicated that (1) only YbB12 is a valence fluctuating compound with the valency of +2.9 at room temperature, (2) the correlation energy between Yb2+ and Yb3+ ions is about 6.0 eV, (3) Tm and Lu ions in the dodecaborides are in a trivalent state, and (4) the binding energy of the 4f level in TmB12 and LuB12 is 5.0 and 7.7 eV, respectively.

High magnetic field studies up to 550 kOe are done on the magnetic and electric properties of YbB12 at low temperatures with special interest in the band gap energy under the field. The gap is quenched around 200 kOe and a large magnetization appears above 450 kOe.

The rare earth hexaborides and dodecaborides have been prepared using a floating zone technique.The rare earth hexaborides exhibit a variety of physical properties ranging from superconductor (YB6), to typical monovalent metal (LaB6), dense Kondo system (CeB6), valence fluctuating system (SmB6), anomalous magnetism based on the narrow gap semiconductor (EuB6), and nonmagnetic narrow gap semiconductor (YbB6).From the measurements of the magnetic susceptibility, electrical resistivity, Hall effect, NMR, XPS and specific heat measurement, it is found that YbB12 exhibits unique behavior uncharacteritic of hitherto studied ytterbium compounds; YbB12 is a mixed valent compound accompanied with the formation of an energy gap. LuB12 is a monovalent metal similar to LaB6.The rare earth hexaborides and dodecaborides have been prepared using a floating zone technique.The rare earth hexaborides exhibit a variety of physical properties ranging from superconductor (YB6), to typical monovalent metal (LaB6), dense Kondo system (CeB6), valence fluctuating system (SmB6), anomalous magnetism based on the narrow gap semiconductor (EuB6), and nonmagnetic narrow gap semiconductor (YbB6).From the measurements of the magnetic susceptibility, electrical resistivity, Hall effect, NMR, XPS and specific heat measurement, it is found that YbB12 exhibits unique behavior uncharacteritic of hitherto studied ytterbium compounds; YbB12 is a mixed valent compound accompanied with the formation of an energy gap. LuB12 is a monovalent metal similar to LaB6.

Magnetic susceptibility, electrical resistivity, Hall effect and L III absorption measurements indicate that YbB 12 exhibits unique behavior uncharacteristic of hitherto studied ytterbium compounds. We suggest that YbB 12 is a valence fluctuating system accompanied with the formation of an energy gap.

Magnetic susceptibility, L III absorption and lattice parameter measurements indicate that Tm valence changes from 3+ to mixed valence with decreasing y in Tm 1− y Yb y B 6 , whereas mixed valence seems to persist even to the single impurity limit in Tm 1− x La x B 6 . These results are compared with experimental one on Sm in the isomorphous alloys.