26 research outputs found
Interplay between Superconductivity and Magnetism in Rb0.8Fe1.6Se2 under Pressure
High-pressure magnetization, structural and 57Fe M\"ossbauer studies were
performed on superconducting Rb0.8Fe1.6Se2.0 with Tc = 32.4 K. The
superconducting transition temperature gradually decreases on increasing
pressure up to 5.0 GPa followed by a marked step-like suppression of
superconductivity near 6 GPa. No structural phase transition in the Fe
vacancy-ordered superstructure is observed in synchrotron XRD studies up to
15.6 GPa, while the M\"ossbauer spectra above 5 GPa reveal the appearance of a
new paramagnetic phase and significant changes in the magnetic and electronic
properties of the dominant antiferromagnetic phase, coinciding with the
disappearance of superconductivity. These findings underline the strong
correlation between antiferromagnetic order and superconductivity in
phase-separated AxFe2-x/2Se2 (A = K, Rb, Cs) superconductors
Intercalation effect on hyperfine parameters of Fe in FeSe superconductor with Tc = 42 K
57Fe-Mossbauer spectra of superconducting beta-FeSe, the Li/NH3 intercalate
product and a subsequent sample of this intercalate treated with moist He gas
have been measured in temperature range 4.7 - 290 K. A correlation is
established between hyperfine parameters and critical temperature Tc in these
phases. A strong increase of isomer shift upon intercalation is explained by a
charge transfer from the Li/NH3 intercalate to the FeSe layers resulting in an
increase of Tc up to 42 K. A significant decrease of the quadrupole splitting
above 240 K has been attributed to diffusive motion of Li+ ions within the
interlamellar space.Comment: 6 pages, 5 figures, 1 tabl
Pressure-induced magnetic collapse and metallization of
The crystal structure, magnetic ordering, and electrical resistivity of
TlFe1.6Se2 were studied at high pressures. Below ~7 GPa, TlFe1.6Se2 is an
antiferromagnetically ordered semiconductor with a ThCr2Si2-type structure. The
insulator-to-metal transformation observed at a pressure of ~ 7 GPa is
accompanied by a loss of magnetic ordering and an isostructural phase
transition. In the pressure range ~ 7.5 - 11 GPa a remarkable downturn in
resistivity, which resembles a superconducting transition, is observed below 15
K. We discuss this feature as the possible onset of superconductivity
originating from a phase separation in a small fraction of the sample in the
vicinity of the magnetic transition.Comment: 12 pages, 5 figure
A RoomâTemperature Verweyâtype Transition in Iron Oxide, FeO
Functional oxides whose physicochemical properties may be reversibly changed at standard conditions are potential candidates for the use in nextâgeneration nanoelectronic devices. To date, vanadium dioxide (VO) is the only known simple transitionâmetal oxide that demonstrates a nearâroomâtemperature metalâinsulator transition that may be used in such appliances. In this work, we synthesized and investigated the crystals of a novel mixedâvalent iron oxide with an unconventional FeO stoichiometry. Near 275â
K, FeO undergoes a Verweyâtype chargeâordering transition that is concurrent with a dimerization in the iron chains and a following formation of new FeâFe chemical bonds. This unique feature highlights FeO as a promising candidate for the use in innovative applications. We established that the minimal FeâFe distance in the octahedral chains is a key parameter that determines the type and temperature of charge ordering. This model provides new insights into chargeâordering phenomena in transitionâmetal oxides in general