arXiv subjects

Mitsuru Itoh

Publications and source records attributed to Mitsuru Itoh.

22 records · Page 2Linked to original sources

arXiv2010

Magnetic structure and spin dynamics of quasi-one-dimensional spin-chain antiferromagnet BaCo2V2O8

We report a neutron diffraction and muon spin relaxation muSR study of static and dynamical magnetic properties of BaCo2V2O8, a quasi-one-dimensional spin-chain system. A proposed model for the antiferromagnetic structure includes: a propagation vector k_AF = (0, 0, 1), independent of external magnetic fields for fields below a critical value H_c(T). The ordered moments, of 2.18 μ_B per Co ion, are aligned along the crystallographic c-axis. Within the screw chains, along the c axis, the moments are arranged antiferromagnetically. In the basal planes the spins are arranged ferromagnetically (forming zig-zags paths) along one of the axis and antiferromagnetically along the other. The temperature dependence of the sub-lattice magnetization is consistent with the expectations of the 3D Ising model. A similar behavior is observed for the internal static fields at different muon stopping sites. Muon time spectra measured at weak longitudinal fields and temperatures much higher than T_N can be well described using a single muon site with an exponential muon spin relaxation that gradually changes into an stretched exponential on approaching T_N. The temperature-induced changes of the relaxation suggest that the Co fluctuations dramatically slow down and the system becomes less homogeneous as it approaches the antiferromagnetic state.

cond-mat.str-el↗

arXiv2009

Ferroelectric Soft Mode in Pb(Mg1/3Nb2/3)O3

Ferroelectric soft mode in Pb(Mg1/3Nb2/3)O3 (PMN) has been clearly resolved by precision Raman scattering measurements for the first time. A polarization direction of the incident laser was chosen along [110] in cubic configuration in order to eliminate strong scattering components around 45 cm-1, which always smeared the low-frequency spectra of PMN. The soft mode frequency omega_s (=\sqrt{omega_0^2-gamma^2}) softens around 200 K, where omega_0 and gamma are a harmonic frequency and a damping constant, respectively. The present result evidenced that the origin of the polarizationthe in PMN is the soft mode.

cond-mat.mtrl-sci↗

arXiv2005

Unusual Dielectric Relaxation in Lightly Doped n-Type Rhombohedral BaTi0.85Zr0.15O3:Ta Ferroelectric Ceramics

The dielectric properties of tantalum doped BaTi0.85Zr0.15O3 were investigated. The conventional solid state reaction method was used to make the ceramic samples. The composition was close to the pinch point of the three structure phase transitions in BaTiO3. Powder X-ray diffraction result indicated that the samples were in very slightly distorted rhombohedral structure at room temperature, and the dielectric measurement showed only cubic-to-rhombohedral phase transition occurred. Instead of a sharp peak characteristic of a ferroelectric (FE) transition, the large dielectric response was similar to those in nonferroelectric perovskites CaCu3Ti4O12, AFe1/2B1/2O3 (A=Ba, Sr, Ca; B=Nb, Ta, Sb) and IBLC (Internal Barrier Layer Capacitance) BaTiO3 based FE ceramics. However, unlike its FE analogue, the conventional BaTiO3 based IBLC ceramics, our samples showed weaker temperature dependence of relative permittivity which spans over a wide temperature range. A Maxwell-Wagner type relaxation in the FE state was observed. Moreover, another relaxation mode appears from the vicinity of FE phase transition temperature TC, and extends over a narrow temperature range, with unusual slowing down of relaxation rate as temperature rises, which is contrary to what is commonly observed. We associate these unusual phenomena with the very slightly distorted rhombohedral structure of our samples and the presence of the grain boundary barrier layer where oxygen vacancies distribute non-homogeneously.

cond-mat.mtrl-sci↗

arXiv2004

Polar Order in Quantum Paraelectric SrTiO3-16 and SrTiO3-18 at Low Temperature

Optical second-harmonic generation (SHG) in SrTi16O3 (STO16) and SrTi18O3 (STO18) was investigated using the SHG microscope. While no-biased STO16 exhibits weak and almost temperature-independent SHG signals, a marked SHG is observed under the electric field in the quantum paraelectric region. In STO18, strong SHG signals appear spontaneously below 36K. However, neutron and X-ray diffraction analyses indicate that no structural change appears at low temperature in STO18, and STO16 under the electric field. By taking into account the fact that the SHG is sensitive to the local polar-order, the combined studies reveals that the long-range order of polar phase does not develop on the both crystals and is frozen in local regions.

cond-mat.mtrl-sci↗