Spin-current-induced modification of the thermal Boltzmann distribution in paramagnetic and ferromagnetic nanostructures
Final Report Abstract
The concept of active cooling of nanoscale devices by the interplay between spin-polarized currents and isolated magnetic moments in a dilute paramagnet is investigated. A bias voltage is used to drive a spinpolarized current through the paramagnetic layer. The spin injectors consist of Fe3Si or CoFeB, respectively, and Cr doped magnesium oxide (MgO) is used as dilute paramagnet. Following the fabrication of the stacked sample structure in ultra-high vacuum (UHV), Cr ions are embedded in the MgO matrix crystal by ion implantation. The sample structure is designed to apply an electric voltage between the ferromagnetic spin injector and the top electrode which results in a spin-polarized current through the dilute paramagnet. The interaction of this current with the paramagnetic moments in their diamagnetic matrix drains energy from the paramagnetic spin system. This is noticed as a cooling effect and is analyzed by electron spin resonance (ESR). Initial attempts to cool a paramagnetic system in MgO through a spin-polarized, electric current failed due to sensitivity and sample fabrication issues. The theory, however, predicts the existence of the effect. The experiments using oleic acid as ESR probe monolayers on iron films were successful: The effect of a spin pumping on a paramagnetic material was detected as a change of the ESR signal amplitude. The transfer of spin angular momentum is detected non-invasively, since no electrical contacts as for the detection by the spin-hall effect are required. It is also shown that this approach allows the analysis of magnetic stray fields and the determination of the temperature of nanoparticles in vitro. The latter offers the perspective to quantify the temperature of nanoparticles for example used in hyperthermia in different media. In summary, it has been possible to develop an ESR-active, multifunctional surface probe that opens the opportunity to design novel devices for spin current detection.
Publications
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Characterization of the oleic acid/iron oxide nanoparticle interface by magnetic resonance. Journal of Magnetism and Magnetic Materials 415, 8 (2016)
S. Masur, B. Zingsem, T. Marzi, R. Meckenstock, M. Farle
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Specific Heat of Low Energy Spin Exitations at elevated Temperature Measured by Ferromagnetic Resonance
B. Zingsem, S. Masur, P. Wendtland, M. Winklhofer, R. Salikov, F. M. Roemer, R.Meckenstock, M. Farle
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Spin-Current Detection via an Interfacial Molecular Paramagnet. Phys. Rev. Applied 10, 054002 (2018)
T. Marzi, R. Meckenstock, S. Masur and M. Farle
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Magnetic anisotropy and relaxation of single Fe/FexOy core/shell- nanocubes: A ferromagnetic resonance investigation. AIP Advances 6, 056119 (2016)
Alexandra Terwey, Ralf Meckenstock, Benjamin Zingsem, Sabrina Masur, Christian Derricks, Florian M. Römer, Michael Farle
