5 research outputs found
Structure and Magnetic Order in the NdFeAs(O,F) Superconductor System
The transition temperature Tc~26 K of the recently discovered superconductor
LaFeAs(O,F) has been demonstrated to be extremely sensitive to the lanthanide
ion, reaching 55 K for the Sm containing oxypnictides. Therefore, it is
important to determine how the moment on the lanthanide affects the overall
magnetism in these systems. Here we report a neutron diffraction study of the
Nd oxypnictides. Long ranged antiferromagnetic order is apparent in NdFeAsO
below 1.96 K. Rietveld refinement shows that both Fe and Nd magnetic ordering
are required to describe the observed data with the staggered moment 1.55(4)
Bohr magneton per Nd and 0.9(1) Bohr magneton per Fe at 0.3 K. The other
structural properties such as the tetragonal-orthorhombic distortion are found
to be very similar to those in LaFeAsO. Neither the magnetic ordering nor the
structural distortion occur in the superconducting sample NdFeAsO0.80F0.20 at
any temperatures down to 1.5 K.Comment: 4 pages, 5 figures, 1 table. Identical to v3, correct HTML front
matter; Scientific data and conclusions the same as in v
Metamagnetic transition in EuFeAs single crystals
We report the measurements of anisotropic magnetization and magnetoresistance
on single crystals of EuFeAs, a parent compound of ferro-arsenide
high-temperature superconductor. Apart from the antiferromagnetic (AFM)
spin-density-wave transition at 186 K associated with Fe moments, the compound
undergoes another magnetic phase transition at 19 K due to AFM ordering of
Eu spins (). The latter AFM state exhibits metamagnetic
transition under magnetic fields. Upon applying magnetic field with at 2 K, the magnetization increases linearly to 7.0 /f.u. at
=1.7 T, then keeps at this value of saturated Eu moments under
higher fields. In the case of , the magnetization increases
step-like to 6.6 /f.u. with small magnetic hysteresis. A metamagnetic
phase was identified with the saturated moments of 4.4 /f.u. The
metamagnetic transition accompanies with negative in-plane magnetoresistance,
reflecting the influence of Eu moments ordering on the electrical
conduction of FeAs layers. The results were explained in terms of
spin-reorientation and spin-reversal based on an -type AFM structure for
Eu spins. The magnetic phase diagram has been established.Comment: 10 pages, 8 figures. accepted for publication in New Journal of
Physics as a special issue articl
Growth and characterization of A_{1-x}K_xFe_2As_2 (A = Ba, Sr) single crystals with x=0 - 0.4
Single crystals of AKFeAs (A=Ba, Sr) with high quality
have been grown successfully by FeAs self-flux method. The samples have sizes
up to 4 mm with flat and shiny surfaces. The X-ray diffraction patterns suggest
that they have high crystalline quality and c-axis orientation. The
non-superconducting crystals show a spin-density-wave (SDW) instability at
about 173 K and 135 K for Sr-based and Ba-based compound, respectively. After
doping K as the hole dopant into the BaFeAs system, the SDW transition
is smeared, and superconducting samples with the compound of
BaKFeAs (0 0.4) are obtained. The
superconductors characterized by AC susceptibility and resistivity measurements
exhibit very sharp superconducting transition at about 36 K, 32 K, 27 K and 23
K for x= 0.40,0.28,0.25 and 0.23, respectively.Comment: 9 pages, 6 figures, 1 table. This paper together with new data are
modified into a new pape