M. Bendele

Coexistence of magnetism and superconductivity in the iron-based compound Cs0.8(FeSe0.98)2.

We report on muon-spin rotation and relaxation (μSR), electrical resistivity, magnetization and differential scanning calorimetry measurements performed on a high-quality single crystal of Cs(0.8)(FeSe(0.98))(2). Whereas our transport and magnetization data confirm the bulk character of the superconducting state below T(c)=29.6(2)  K, the μSR data indicate that the system is magnetic below T(N)=478.5(3)  K, where a first-order transition occurs. The first-order character of the magnetic transition is confirmed by differential scanning calorimetry data. Taken all together, these data indicate in Cs(0.8)(FeSe(0.98))(2) a microscopic coexistence between the superconducting phase and a strong magnetic phase. The observed T(N) is the highest reported to date for a magnetic superconductor.

Pressure induced static magnetic order in superconducting FeSe1-x.

We report on a detailed investigation of the electronic phase diagram of FeSe1-x under pressures up to 1.4 GPa by means of ac magnetization and muon-spin rotation. At a pressure approximately 0.8 GPa the nonmagnetic and superconducting FeSe1-x enters a region where static magnetic order is realized above T{c} and bulk superconductivity coexists and competes on short length scales with the magnetic order below T{c}. For even higher pressures an enhancement of both the magnetic and the superconducting transition temperatures as well as of the corresponding order parameters is observed. These exceptional properties make FeSe1-x to be one of the most interesting superconducting systems investigated extensively at present.

Synthesis, crystal structure, and chemical stability of the superconductor FeSe1−x

We report on a comparative study of the crystal structure and the magnetic properties of FeSe1−x (x=0.0–0.15) superconducting samples by neutron powder-diffraction and magnetization measurements. The samples were synthesized by two different methods: a “low-temperature” one using powders as a starting material at T≃700 °C and a “high-temperature” method using solid pieces of Fe and Se at T≃1075 °C. The effect of a starting (nominal) stoichiometry on the phase purity of the obtained samples, the superconducting transition temperature Tc, as well as the chemical stability of FeSe1−x at ambient conditions were investigated. It was found that in the Fe-Se system, a stable phase exhibiting superconductivity at Tc≃8 K exists in a narrow range of selenium concentration (FeSe0.974±0.005).

Tuning the superconducting and magnetic properties of Fe y Se 0.25 Te 0.75 by varying the iron content

The superconducting and magnetic properties of FeySe0.25Te0.75 single crystals (0.9≤y≤1.1) were studied by means of x-ray diffraction, superconducting quantum interference device magnetometry, muon-spin rotation, and elastic neutron diffraction. The samples with y<1 exhibit coexistence of bulk superconductivity and incommensurate magnetism. The magnetic order remains incommensurate for y≥1 but with increasing Fe content superconductivity is suppressed and the magnetic correlation length increases. The results show that the superconducting and the magnetic properties of the FeySe1−xTex can be tuned not only by varying the Se/Te ratio but also by changing the Fe content. ©2010 The American Physical Society

Coexistence of incommensurate magnetism and superconductivity in Fe 1 + y Se x Te 1 − x

We have studied the superconducting and magnetic properties of

Evolution of two-gap behavior of the superconductor FeSe1-x.

{\text{Fe}}_{1+y}{\text{Se}}_{x}{\text{Te}}_{1\ensuremath{-}x}

Evolution of two-gap behavior of the superconductor FeSe_{1-x}

single crystals

Effect of external pressure on the magnetic properties of LnFeAsO (Ln = La, Ce, Pr, Sm)

(0\ensuremath{\le}x\ensuremath{\le}0.5)

Magnetic excitations of Fe1 + ySexTe1 − x in magnetic and superconductive phases

by magnetic susceptibility, muon-spin rotation, and neutron diffraction. We find three regimes of behavior: (i) commensurate magnetic order for

Pressure-induced ferromagnetism in antiferromagnetic Fe1.03Te

x\ensuremath{\lesssim}0.1