27 research outputs found
Magnetic-crystallographic phase diagram of superconducting parent compound FeTe
hrough neutron diffraction experiments, including spin-polarized
measurements, we find a collinear incommensurate spin-density wave with
propagation vector () at base
temperature in the superconducting parent compound FeTe. This critical
concentration of interstitial iron corresponds to and leads
crystallographic phase separation at base temperature. The spin-density wave is
short-range ordered with a correlation length of 22(3) \AA, and as the ordering
temperature is approached its propagation vector decreases linearly in the
H-direction and becomes long-range ordered. Upon further populating the
interstitial iron site, the spin-density wave gives way to an incommensurate
helical ordering with propagation vector () at base temperature. For a sample with , we
also find an incommensurate spin-density wave that competes with the
bicollinear commensurate ordering close to the N\'eel point. The shifting of
spectral weight between competing magnetic orderings observed in several
samples is supporting evidence for the phase separation being electronic in
nature, and hence leads to crystallographic phase separation around the
critical interstitial iron concentration of 12%. With results from both powder
and single crystal samples, we construct a magnetic-crystallographic phase
diagram of FeTe for $ 5% < x <17%
AND/R: Advanced neutron diffractometer/reflectometer for investigation of thin films and multilayers for the life sciences
An elastic neutron scattering instrument, the advanced neutron diffractometer/reflectometer (AND/R), has recently been commissioned at the National Institute of Standards and Technology Center for Neutron Research. The AND/R is the centerpiece of the Cold Neutrons for Biology and Technology partnership, which is dedicated to the structural characterization of thin films and multilayers of biological interest. The instrument is capable of measuring both specular and nonspecular reflectivity, as well as crystalline or semicrystalline diffraction at wave-vector transfers up to approximately 2.20 Å(-1). A detailed description of this flexible instrument and its performance characteristics in various operating modes are given.D. J. M. is supported
through a NSF NIRT grant Contract No. 0304062
Spiral Spin Structures and Origin of the Magnetoelectric Coupling in YMn\u3csub\u3e2\u3c/sub\u3eO\u3csub\u3e5\u3c/sub\u3e
By combining neutron four-circle diffraction and polarized neutron-diffraction techniques we have determined the complex spin structures of a multiferroic YMn2O5 that exhibits two ferroelectric phases at low temperatures. The obtained magnetic structure has spiral components in both the low-temperature ferroelectric phases that are magnetically commensurate and incommensurate, respectively. Among proposed microscopic theories for the magnetoelectric coupling, our results are consistent with both the spin-current mechanism and the magnetostriction mechanism. Our results also explain why the electric polarization changes at the low-temperature commensurate-to-incommensurate phase transition