Takayuki Tajiri

Magnetic Behavior of Fe Doped In2O3

We report spin-glass transition at room temperature (RT) and cluster-glass behavior below RT for Fe doped In2O3 powders with the atomic ratio of In : Fe = 1.85 : 0.15 grown in an oxygen atmosphere. In ac susceptibility, a large peak and a small cusp were observed at RT and ≈30 K, respectively. The peak at RT shifted to higher temperatures with an increase of applied field frequency, while the cusp showed no frequency dependence. Third harmonic nonlinear susceptibility exhibited a divergent peak at RT. Field-cooled dc susceptibility increased almost linearly below RT, whereas zero-field-cooled dc susceptibility deviated below the field-cooled one with lowering temperature.

Effects of hydrogen in working gas on valence States of oxygen in sputter-deposited indium tin oxide thin films.

X-ray photoelectron spectroscopy (XPS) and Rutherford backscattering spectroscopy-elastic recoil detection analysis (RBS-ERDA) revealed that hydrogen in working gas for dc-plasma sputter deposition resided in indium tin oxide (ITO) films and generated the O(-) state seen as the suboxide-like O 1s peak in XPS. Growth of the suboxide-like O 1s peak was parallel with an increase of the resided hydrogen quantified by RBS-ERDA. The first-principles band structure calculation revealed that the electronic structure of In(2)O(3) crystal was realized typically for the most conductive as-deposited film grown in the gas containing hydrogen of 1%. The as-deposited film grown in the gas containing hydrogen of more than 1% exhibited rather high density but low mobility of carriers and showed the electronic structure above 4 eV originated from the O(-) state due to the resided hydrogen in addition to that of the most conducting one. Both well preserved In(2)O(3) band structure and proper concentration of the O(2-) vacancy are indispensable for achieving the highest conductivity; however, the O(-) state lowers efficiency of the carrier doping using the O(2-) vacancy in the lattice and increases density of the ionized scattering center for the carriers.

Fabrication of a single layer graphene by copper intercalation on a SiC(0001) surface

Cu atoms deposited on a zero layer graphene grown on a SiC(0001) substrate, intercalate between the zero layer graphene and the SiC substrate after the thermal annealing above 600 °C, forming a Cu-intercalated single layer graphene. On the Cu-intercalated single layer graphene, a graphene lattice with superstructure due to moire pattern is observed by scanning tunneling microscopy, and specific linear dispersion at the K¯ point as well as a characteristic peak in a C1s core level spectrum, which is originated from a free-standing graphene, is confirmed by photoemission spectroscopy. The Cu-intercalated single layer graphene is found to be n-doped.

Novel Size Effect of LaMnO3+δ Nanocrystals Embeded in SBA-15 Mesoporous Silica

LaMnO 3+δ nanocrystals with a mean diameter of 75 A, were synthesized using SBA-15 mesoporous silica. The magnetic properties of the nanocrystals showed a novel size effect and were quite different from those of bulk crystal. The magnetic and electron spin resonance measurement results indicate that the existence of two transition temperatures, 278 and 235 K, which are higher than Neel and Curie temperature of bulk LaMnO 3+δ . The ESR spectrum was observed even at the lower transition temperature and consisted of the two broad lines whose shape changed at each transition temperature. The magnetization curve at 77 K was well reproduced by the summation of the two superparamagnetic magnetizations corresponding to antiferromagnetic and ferromagnetic nanoparticles, respectively. These results suggest that there are noninteracting ferromagnetic and antiferromagnetic nanoparticles with transition temperatures of 278 and 235 K, respectively.

Phase Separation in La1-xSrxMnO3+δ Nanocrystals Studied by Electron Spin Resonance

Nanocrystals of La 1- x Sr x MnO 3+δ (0< x ≤0.51) with a diameter of about 8 nm were synthesized in the pores of the mesoporous silica SBA-15. The crystal structure at all Sr concentrations had a rhombohedral symmetry. The temperature dependence of the magnetization showed ferromagnetic and superparamagnetic behavior, and the magnetization curves indicate the coexistence of a ferromagnetic and an antiferromagnetic component. ESR spectra were observed even at 77 K and were well reproduced by the summation of two absorption lines with either a Gaussian or a Lorentzian profile. The temperature dependence in the ESR spectra suggests the coexistence of two components with two transition temperatures. The magnetic phase of the nanocrystals indicates the coexistence of a ferromagnetic and an antiferromagnetic phase at all Sr concentrations studied (0< x ≤0.51), with a smooth Sr dependence of the two transition temperatures. The experimental results suggest the existence of a phase separation into a ferromagnetic...

Effects of anisotropic strain on perovskite LaMnO3+δ nanoparticles embedded in mesoporous silica

We applied anisotropic stress to LaMnO3+δ nanoparticles synthesized in one-dimensional pores of mesoporous silica and investigated the effects of the anisotropic strain on the nanoparticles, which consisted of ferromagnetic and antiferromagnetic particles. The nanoparticles in the one-dimensional pores were crushed without stress in the direction parallel to the silica walls that separated the pores when the mesoporous silica containing the nanoparticles is pressurized. X-ray diffraction patterns of the nanoparticles indicated that the lattice strain increased with increasing applied pressure. The lattice constants were found to reduce anisotropically, and the values saturated above a critical strain. Both the ferromagnetic and antiferromagnetic transition temperatures for the LaMnO3+δ nanoparticles initially increased with increasing pressure and then remained constant at around the critical strain. These results indicate that anisotropic stress causes distortion of the shape of nanoparticles. This induc...

Investigation of structural changes in chiral magnet Cr1∕3NbS2 under application of pressure

We perform structural analysis experiments on the chiral magnet Cr1∕3NbS2, in which Cr3+ ions are inserted between hexagonal NbS2 layers. The noncentrosymmetrical nature of the inserted Cr3+ appears as a distorted CrS6 octahedron. Under the application of hydrostatic pressure, the lattice shrinks significantly along the c-axis rather than the a-axis. However, at a pressure P of approximately 3–4 GPa, a kink in the rate of decrease in the lattice parameters is observed, and the slight movement of a Nb atom along the c-axis brings about a decrease in the distortion of the CrS6 octahedron. This structural change qualitatively suggests a decrease in the strength of the Dzyaloshinskii-Moriya (D-M) interaction. Under hydrostatic pressure, the magnetic ordering temperature TC decreases, and dTC/dP exhibits a slight change at around 3 GPa. A series of experiments indicates that the change in the structural symmetry of the CrS6 octahedron influences the exchange network between Cr3+ ions as well as the D-M interac...

Uniaxial Strain Effects on Cuprate Superconductor YBa2Cu4O8

The uniaxial strain effects on the cuprate superconductor YBa 2 Cu 4 O 8 (Y-124) were investigated by magnetic measurements and quantitatively compared with those of hydrostatic contraction up to 1...

Synthesis and Magnetic Property of Multiferroic BiMnO3 Nanoparticles in the Pores of Mesoporous Silica

The mesoporous silica material SBA-15 was prepared with control pore size for use as a nanoparticle synthesis template. The X-ray diffraction results show that the nanopores were ordered in a hexagonal structure. The pore size was controlled by the synthesis conditions. Nanoparticles of the multiferroic compound BiMnO3 with an average size of about 14 nm were successfully synthesized in the pores of SBA-15, and their magnetic properties were investigated. The prepared BiMnO3 nanoparticles showed both antiferromagnetic and ferromagnetic behavior, whereas BiMnO3 bulk crystals consistently showed ferromagnetic behavior. The prepared BiMnO3 nanoparticles exhibited unique magnetic size effects: the appearance of antiferromagnetic behavior and the coexistence of antiferromagnetic and ferromagnetic components.

Superparamagnetic behavior of La1−xSrxMnO3 nanoparticles in the MCM-41 molecular sieve

Abstract La1−xSrxMnO3 nanoparticles were prepared by calcination of a molecular sieve MCM-41 soaked in precursor solution. Magnetic properties have been investigated by the magnetization measurements. Superparamagnetic behavior of the nanoparticles is observed both for the antiferromagnetic and ferromagnetic phases at low temperatures. For the antiferromagnetic phase, the superparamagnetic moment corresponds to the uncompensated moments in the antiferromagnetic particles. While for the superparamagnetism for the ferromagnetic phase is smaller than the superparamagnetism estimated for the single-domain ferromagnetic particles.