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MA: Fachverband Magnetismus
MA 14: General Spintronics
MA 14.6: Vortrag
Montag, 16. März 2020, 16:15–16:30, HSZ 401
Evidence for Magnetic Polarons in the Ferromagnetic Semiconductor HgCr2Se4? – A Fluctuation Spectroscopy Study — •Merlin Mitschek1, Shuai Yang2, Yongqing Li2, and Jens Müller1 — 1Institute of Physics, Goethe-University, Frankfurt (Main), Germany — 2Institute of Physics, Chinese Academy of Sciences, Beijing, China
Semiconducting HgCr2Se4 is a member of the spinel family of compounds where one can observe a colossal magnetoresistance (CMR) effect, a field of research that expanded the knowledge of electronic correlations, phase transitions and magnetism. The complexity of the physics underlying the CMR makes it desirable to study a preferably simple system, where the relevant degrees of freedom, including spin, charge, orbital and lattice, along with disorder and strong electron correlations are less intertwined. A typical model system is EuB6 [1] and also HgCr2Se4, where the phase transition from the paramagnetic to the ferromagnetic phase coincides with an insulator-to-metal transition at TC ≈ 105 K. The CMR effect [2] is found to strongly depend on the degree of disorder in the samples. In our noise measurements, we find 1/fα-type fluctuation spectra from room temperature down to low temperatures. The normalized resistance noise power spectral density (PSD) increases by nearly two orders of magnitude upon approaching TC. For 100 K < T < 150 K, we observe superimposed Lorentzian spectra originating in single two-level processes. We discuss our findings in terms of a model of percolating magnetic polarons.
[1] PRB 86, 184425,
[2] PRB 94, 224404.