arXiv subjects

S. Iguchi

Publications and source records attributed to S. Iguchi.

23 records · Page 2Linked to original sources

arXiv2006

Impurity-doping induced ferroelectricity in frustrated antiferromagnet CuFeO2

Dielectric responses have been investigated on the triangular-lattice antiferromagnet CuFeO2 and its site-diluted analogs CuFe1-xAlxO2 (x=0.01 and 0.02) with and without application of magnetic field. We have found a ferroelectric behavior at zero magnetic field for x=0.02. At any doping level, the onset field of the ferroelectricity always coincides with that of the noncollinear magnetic structure while the transition field dramatically decreases to zero field with Al doping. The results imply the further possibility of producing the ferroelectricity by modifying the frustrated spin structure in terms of site-doping and external magnetic field.

cond-mat.str-el↗

arXiv2005

Magneto-optics induced by the spin chirality in itinerant ferromagnet Nd$_2$Mo$_2$O$_7$

It is demonstrated both theoretically and experimentally that the spin chirality associated with a noncoplanar spin configuration produces a magneto-optical effect. Numerical study of the two-band Hubbard model on a triangle cluster shows that the optical Hall conductivity $σ_{xy}(ω)$ is proportional to the spin chirality. The detailed comparative experiments on pyrochlore-type molybdates $R_2$Mo$_2$O$_7$ with $R=$Nd (Ising-like moments) and $R=$Gd (Heisenberg-like ones) clearly distinguishes the two mechanisms, i.e., spin chirality and spin-orbit interactions. It is concluded that for $R$=Nd, $σ_{xy}(ω)$ is dominated by the spin chirality for the dc ($ω=0$) and the $d \to d$ incoherent intraband optical transitions between Mo atoms.

cond-mat.str-el↗

arXiv2004

Chemical Control of Spin Chirality in $(Nd_{1-x} Dy_x)_2 Mo_2 O_7$

Magnetization and Hall resistivity have been investigated for single crystals of Dy-doped Nd$_{2}$Mo$_{2}$O$_{7}$. A sharp decrease of the Hall resistivity upon a metamagnetic transition, perhaps associated with magnetic-field ($H$) induced flop of Dy$^{3+}$ moments, has been observed in the Dy-doped crystals only for $H \parallel [111]$ direction. In addition, the sign of the Hall resistivity at a high field, both for $H \parallel [100]$ and for $H \parallel [111]$, changes with the Dy-doping. These results are explained in terms of the sign change of Mo spin chirality that is controlled by the Dy$^{3+}$ moments with a different sign of $f$-$d$ interaction from the Nd$^{3+}$ moments.

cond-mat.str-el↗

arXiv2003

Orbital Motion in the Radio Galaxy 3C 66B: Evidence for a Supermassive Black Hole Binary

Supermassive black hole binaries may exist in the centers of active galactic nuclei like quasars and radio galaxies and mergers between galaxies may result in the formation of supermassive binaries during the course of galactic evolution. Using the very-long-baseline interferometer, we imaged the radio galaxy 3C 66B at radio frequencies and found that the unresolved radio core of 3C 66B shows well-defined elliptical motions with a period of 1.05 +/- 0.03 years, which provides a direct detection of a supermassive black hole binary.

astro-ph↗

arXiv2000

Pair Plasma Dominance in the Parsec-Scale Relativistic Jet of 3C345

We investigate whether a pc-scale jet of 3C345 is dominated by a normal plasma or an electron-positron plasma. We present a general condition that a jet component becomes optically thick for synchrotron self-absorption, by extending the method originally developed by Reynolds et al. The general condition gives a lower limit of the electron number density, with the aid of the surface brightness condition, which enables us to compute the magnetic field density. Comparing the lower limit with another independent constraint for the electron density that is deduced from the kinetic luminosity, we can distinguish the matter content. We apply the procedure to the five components of 3C345 (C2, C3, C4, C5, and C7) of which angular diameters and radio fluxes at the peak frequencies were obtainable from literature. Evaluating the representative values of Doppler beaming factors by their equipartition values, we find that all the five components are likely dominated by an electron-positron plasma. The conclusion does not depend on the lower cutoff energy of the power-law distribution of radiating particles.

astro-ph↗