In-situ studies of the correlations between electrochemical processes and magnetic properties
Stefan Topolovec
Institue of Materials Physics, Graz UNiversity of Technology
15:20 - 16:00 Friday 26 June 2015 HS 05.12 Physikgebaeude, Universitätsplatz 5

The combination of magnetism and electrochemistry has attracted considerable attention in the last years. On the one hand, a promising research field was recently opened up with in-situ studying the influence of electrochemical charging processes on the magnetic properties of high-surface area porous nanomaterials and thin films. Another application-relevant aspect of the combination of magnetism and electrochemistry pertains to in-situ studies of the electrodeposition of magnetic thin films.

In both cases the control of magnetic properties by electrochemical processes demands appropriate in-situ measurement techniques. By designing a three-electrode electrochemical cell for operation in a commercial state-of-the-art SQUID magnetometer, which allows the simultaneous measurement of magnetization and cyclic voltammograms, we have developed a new approach for studying the correlation between electrochemical processes and magnetic properties. This will be illustrated based on three issues: (i) The tunability of the magnetic moment of porous nanophase systems by electrochemical charging, (ii) the electrodeposition of thin Co films and (iii) charging induced variations of the magnetic moment of Li-ion battery materials.

(i) Using this setup we could show that the magnetic moment of γ-Fe2O3 [1] and Pt [2] nanoparticles can be varied reversible up to several percent by electrochemical charging. The observed variations are due to reversible redox reactions, respectively to electric field induced effects.

(ii) Furthermore, the cell [3] was used to study the evolution of the absolute magnetic moment during the electrodeposition of magnetic thin films. Thus, we could show that thin ferromagnetic Co films have an enhanced magnetic moment compared to the bulk value.

(iii) In addition, the in-situ measurement technique was applied to monitor the magnetic moment of LiCoO₂ cathodes during charging and discharging. These measurements revealed that in-situ measurements of the magnetic moment are a new, promising technique to study atomic and chemical processes in the cathode material during the charging process. For instance, it was shown, that in addition to Co also O undergoes partial oxidation during charging.

[1] S. Topolovec, P. Jerabek, D.V. Szabó, H. Krenn, R. Würschum, J. Magn. Magn. Mater. 329 (2013) 43.

[2] E.-M. Steyskal, S. Topolovec, S. Landgraf, H. Krenn, R. Würschum, Beilstein J. Nanotechnol. 4 (2013) 394.

[3] S.Topolovec, H.Krenn, R. Würschum, Rev. Sci. Instrum. 86 (2015) 063903.