40 research outputs found
Can antiferromagnetism and superconductivity coexist in the high-field paramagnetic superconductor Nd(O,F)FeAs?
We present measurements of the temperature and field dependencies of the
magnetization M(T,H) of Nd(O0.89F0.11)FeAs at fields up to 33T, which show that
superconductivity with the critical temperature Tc ~ 51K cannot coexist with
antiferromagnetic ordering. Although M(T,H) at 55 < T < 140K exhibits a clear
Curie-Weiss temperature dependence corresponding to the Neel temperature TN ~
11-12K, the behavior of M(T,H) below Tc is only consistent with either
paramagnetism of weakly interacting magnetic moments or a spin glass state. We
suggest that the anomalous magnetic behavior of an unusual high-field
paramagnetic superconductor Nd(O1-xFx)FeAs is mostly determined by the magnetic
Nd ions.Comment: 4 pages, 4 figure
Spin Ordering in LaOFeAs and Its Suppression in Superconductor LaO0.89F0.11FeAs Probed by M\"ossbauer Spectroscopy
The 57Fe M\"ossbauer spectroscopy was applied to an iron-based layered
superconductor LaO0.89F0.11FeAs with a transition temperature of 26 K and its
parent material LaOFeAs. Throughout the temperature range from 4.2 to 298 K, a
singlet spectrum with no magnetic splitting was observed as a main component of
each M\"ossbauer spectrum of the F-doped superconductor. No additional internal
magnetic field was observed for the spectrum measured at 4.2 K under a magnetic
field of 7 T. On the other hand, the parent LaOFeAs shows a magnetic transition
at around 140 K, and this temperature is slightly lower than that of a
structural phase transition from tetragonal to orthorhombic phase, which
accompanies the resistivity anomaly at around 150 K. The magnetic moment is
estimated to be ~0.35 B/Fe at 4.2 K in the orthorhombic phase, and the
spin disorder remains in the magnetic ordered state even at 4.2 K. The fact
that no magnetic transition in LaO0.89F0.11FeAs was observed even at 4.2 K
under 7 T implies a strong spin fluctuation above Tc or small magnetic moment
in this system. Therefore, the present results show that the F-doping
effectively suppresses the magnetic and structural transitions in the parent
material and the suppression leads to emergence of superconductivity in this
system.Comment: 13 pages, 4 figure
MAGNETIC PROPERTIES OF Cr2S3-xSex and CrS1.17-xSex SYSTEMS
It was found that the transition from ferrimagnetism to antiferromagnetism takes place at about x = 1.8 in Cr2S3-xSex system and the slope of the concentration dependency of the magnetization changes at x = 0.065 in CrS1.17-xSex system and that the lattice parameters discontinuously changed at about the magnetic transition point