ABSTRACT

The discoveries of superconductivity in Fe-and Ni-based layered

pnictide compounds1-3 have generated tremendous interest in con-

densed matter community. For the iron-based compounds, not only

could they have high superconducting transition temperatures4-6

but also show intriguing interplay between structure, magnetism

and superconductivity. The undoped compounds commonly display

the structural and magnetic phase transitions, which, depending

on materials, could occur either at the same temperature or

separately.7-9 Upon electron or hole doping or application of

pressure, both the magnetic order and the structural transition are

suppressed, and superconductivity emerges.8,10,11 A variety of Fe-

based superconductors with different structures have been discov-

ered. Based on the magnetic structures of the parent compounds,

Figure 5.1 Three different types of magnetic structures for the parent compounds of Fe-based superconductors.