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TT: Fachverband Tiefe Temperaturen

TT 19: Poster Session: Correlated Electrons 1

TT 19.16: Poster

Montag, 20. März 2017, 15:00–19:00, P2-EG

Spin dynamics of FeGa_3−xGe_x studied by Electron Spin Resonance — Bonho Koo¹, Kristian Bader², Michael Baenitz¹, Peter Gille², and •Jörg Sichelschmidt¹ — ¹MPI für Chemische Physik fester Stoffe, Dresden — ²LMU, Kristallographie, München

FeGa₃ is a nonmagnetic, narrow-gap semiconductor which acquires itinerant ferromagnetism upon electron doping by a partial replacement of Ga with Ge. The way how this magnetism evolves is of particular interest for better understanding the d-electron heavy-fermion behaviour of FeGa_3−xGe_x (at x<0.15) or the properties close to a ferromagnetic (FM) quantum critical point at the critical Ge-concentration of x=0.15. For detailed studies in this direction the availability of single crystals with a high purity is a precondition.

We studied the electron spin resonance (ESR) of ultra-pure single crystals of FeGa_3−xGe_x for x=0 and x around 0.15. For x=0 we observed a well-defined ESR signal, indicating the presence of pre-formed magnetic moments in the semiconducting phase. Upon increasing x the occurrence of itinerant magnetism clearly affects the ESR properties below T≈30 K whereas at higher T an ESR signal as seen in FeGa₃ prevails independent on the Ge-content. We interpret the low-T ESR in terms of a resonance of conduction electron spins and consider the relaxation as being determined by exchange fields. This is supported by a comparison with the temperature dependencies of magnetisation and electrical resistivity. The present results show that the ESR of FeGa_3−xGe_x is an appropriate and direct tool to investigate FM correlations in the vicinity of a FM quantum critical point.