Electric Control of Spin Helicity in a Magnetic Ferroelectric

Magnetic ferroelectrics or multiferroics, which are currently extensively explored, may provide a good arena to realize a novel magnetoelectric function. Here we demonstrate the genuine electric control of the spiral magnetic structure in one of such magnetic ferroelectrics, TbMnO3. A spin-polarized neutron scattering experiment clearly shows that the spin helicity, clockwise or counter-clockwise, is controlled by the direction of spontaneous polarization and hence by the polarity of the small cooling electric field.Comment: 4 pages, 3 figure

Monolithic Ge:Ga Detector Development for SAFARI

We describe the current status and the prospect for the development of monolithic Ge:Ga array detector for SAFARI. Our goal is to develop a 64x64 array for the 45 -- 110 um band, on the basis of existing technologies to make 3x20 monolithic arrays for the AKARI satellite. For the AKARI detector we have achieved a responsivity of 10 A/W and a read-out noise limited NEP (noise equivalent power) of 10^-17 W/rHz. We plan to develop the detector for SAFARI with technical improvements; significantly reduced read-out noise with newly developed cold read-out electronics, mitigated spectral fringes as well as optical cross-talks with a multi-layer antireflection coat. Since most of the elemental technologies to fabricate the detector are flight-proven, high technical readiness levels (TRLs) should be achieved for fabricating the detector with the above mentioned technical demonstrations. We demonstrate some of these elemental technologies showing results of measurements for test coatings and prototype arrays.Comment: To appear in Proc. Workshop "The Space Infrared Telescope for Cosmology & Astrophysics: Revealing the Origins of Planets and Galaxies". Eds. A.M. Heras, B. Swinyard, K. Isaak, and J.R. Goicoeche

Weakening of the diamagnetic shielding in FeSe1−x_{1-x}Sx_x at high pressures

The superconducting transition of FeSe$_{1-x}$S$_x$ with three distinct sulphur concentrations $x$ was studied under hydrostatic pressure up to $\sim$70 kbar via bulk AC susceptibility. The pressure dependence of the superconducting transition temperature ($T_c$) features a small dome-shaped variation at low pressures for $x=0.04$ and $x=0.12$, followed by a more substantial $T_c$ enhancement to a value of around 30 K at moderate pressures. In $x=0.21$, a similar overall pressure dependence of $T_c$ is observed, except that the small dome at low pressures is flattened. For all three concentrations, a significant weakening of the diamagnetic shielding is observed beyond the pressure around which the maximum $T_c$ of 30 K is reached near the verge of pressure-induced magnetic phase. This observation points to a strong competition between the magnetic and high-$T_c$ superconducting states at high pressure in this system.Comment: 5 pages, 4 figures + Supplemental Material (2 pages, 3 figures). Accepted for publication in Phys. Rev. B (Rapid Comm.

Anisotropic magnetic diffuse scattering in an easy-plane type antiferromagnet ErNi2_{2}Ge2_{2}

We report on neutron scattering studies of a rare earth intermetallic compound ErNi$_{2}$Ge$_{2}$. Polarized neutron scattering experiments revealed that the magnetic ordered moment ${\bm m}$ lies in ab-plane. Taking account of a lack of the third higher harmonic reflection, ErNi$_{2}$Ge$_{2}$ is considered to have a helical magnetic structure. The magnetic scattering profiles along the $[100]^{\ast}$- and the $[110]^{\ast}$-directions are well described by the sum of Gaussian and modified-Lorentzian terms, even far below $T_{\scriptsize N}$, indicating that short-range orders coexist with a long-range order. Interestingly, the modified-Lorentzian-type diffuse scattering is not present in the profiles along the $[001]^{\ast}$-direction. The anisotropy of the diffuse scattering suggests that the short-range-order consists of one dimensional long-range helices along the c-axis.Comment: 4 pages, to be published in J. Phys.: Condens. Matter (HFM2008