Regensburg 2019 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 51: Magnetism Poster B
MA 51.53: Poster
Donnerstag, 4. April 2019, 15:00–18:00, Poster C
Fluctuation spectroscopy of the ferromagnetic semiconductor HgCr2Se4 — •Merlin Mitschek1, Shuai Yang2, Yongqing Li2, and Jens Müller1 — 1Physikalisches Institut, Goethe-Universität, Frankfurt am Main, Germany — 2Institue of Physics, Chinese Academy of Sciences, Beijing, China
HgCr2Se4 has been well known for several years as a member of the spinel family where one can observe the colossal magnetoresistance (CMR) effect, a field of research that expanded the knowledge of electron correlations, phase transitions and magnetism.
The complexity of the physics behind 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 as, e.g., for the mixed-valence perovskite manganites. This is true for the model system EuB6 [1], and also for HgCr2Se4, which exhibits MR ratios of up to five orders of magnitude [2]. The phase transition from the paramagnetic to the ferromagnetic phase coincides with an insulator-metal transition at TC ≈ 105 K. Strikingly, the CMR effect is most pronounced when spin correlations between superexchange-coupled Cr3+ are significant. As a powerful probe to test possible scenarios for explaining the CMR effect, we employ fluctuation (noise) spectroscopy [1]. We analyze and discuss the observed generic 1/f-type noise below the transition, which is superimposed by distinct two-level fluctuations above TC, in terms of a model of percolating magnetic polarons.
Phys. Rev. B 94, 224404,(2016).
[2] Phys. Rev. B 86, 184425, (2012).