Dresden 2011 – scientific programme

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MA: Fachverband Magnetismus

MA 4: Magnetic Coupling Phenomena/ Exchange Bias

MA 4.7: Talk

Monday, March 14, 2011, 12:30–12:45, HSZ 403

Magnetic avalanches in mixed valence oxide spin-glass — •Michalis Charilaou^1,2, Shuangyi Zhao³, Jörg F. Löffler², and Andreas U. Gehring¹ — ¹Earth and Planetary Magnetism, Department of Earth Sciences, ETH Zurich, Sonneggstrasse 5, 8092 Zurich, Switzerland — ²Laboratory of Metal Physics and Technology, Department of Materials, ETH Zurich, Wolfgang-Pauli-Strasse 10, 8093 Zurich, Switzerland — ³Laboratory for Solid State Physics, Department of Physics, ETH Zurich, Schafmattstrasse 16, 8093 Zurich, Switzerland

We report sharp jumps (avalanches) of the magnetic moment in polycrystalline hemo-ilmenite solid solution (x)FeTiO₃– (1-x)Fe₂O₃ with x=0.8 at low temperature (T< 2.75 K). The avalanches occur at a critical trigger-field H_cr upon field reversal and are symmetric on either side of the magnetization loop m(H). The number of jumps increases with decreasing temperature reaching a total of 4 on either side of the m(H) loop at T=0.75 K. Extensive study shows that the magnetization loops at each temperature are fully reproducible and statistical analysis reveals that the intensity of the jumps decreases with increasing trigger field. Moreover, a small increase (1%) of the sample temperature can be measured right after a jump indicating the release of thermal energy.

The experimental findings indicate that avalanches in this system are due to competing exchange and superexchange Fe(II)–Fe(III) interactions.