Muon spectroscopy has shown itself to be an extremely versatile and powerful probe of magnetic properties of materials. Never more so than in the recent discovery of the iron-pnictide superconductors, the so-dubbed “iron age” of superconductivity. Indeed, it has the unique ability to detect weak and strongly disorder magnetic states and it provides reliable and direct information about the volume fractions of the magnetic and superconducting phases [1,2]. One of the most interesting phenomena discovered by muons is that for some members of the pnictide family, the magnetic and the superconducting areas are separated microscopically, showing an abrupt (first-order-like) transition between the magnetic and the superconducting phases [3]. However, in other materials magnetism is continuously suppressed and superconductivity is enhanced by changing the charge doping, with a crossover region where bulk magnetism and bulk superconductivity to spatially coexist [1,2,4]. I will spend the first part of my presentation discussing these pheneomena, whilst introducing some of the fundamentals of the muon spectroscopy technique.

[1] A. J. Drew et al., Physical Review Letters 101, 097010 (2008)

[2] A. J. Drew et al., Nature Materials 8, 310 - 314 (2009)

[3] J. T. Park & A. J. Drew et al., Physical Review Letters 102, 117006 (2009)

[4] P. Marsik & A. J. Drew et al., Physical Review Letters 105, 057001 (2010)