| Using a broad spectrum of experimental techniques, such as NMR µSR, ESR, ARPES, STM/STS, magnetometry, and transport measurements we have studied the physical properties of doped LiFeAs. The stoichiometric compound shows superconductivity below Tc = 18 K. Both, doping with electrons and holes causes a strong suppression of the transition temperature. In strongly hole doped compounds which are realized by reducing the Li content a ferromagnetic state is observed below 150 K. The ferromagnetic order is seen in magnetisation measurements, from As-NQR data, from µSR data, and from a pronounced ferromagnetic resonance signal. The observed average moment of ~0.1 µB/Fe is small, but the data from the local probe techniques clearly show that the whole sample shows a magnetic order below 150 K. The relationship between this unusual ferromagnetic state and anomalous observations in superconducting LiFeAs are discussed. |
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