Field control of bound magnetic polarons in magnetic oxides (ConBMP)
Final Report Abstract
Throughout the project we continuously fabricated magnetic ZnO thin films with different magnetic ion concentration and species by pulsed laser deposition. We performed the standard characterization of magnetic ZnO by magnetization and magnetotransport measurements. In order to understand the transport, magnetization, and magnetooptical properties of magnetic semiconductors with bound magnetic polarons (BMP), it is significant to describe the volume of magnetic semiconductor where BMP are formed. This volume can only be determined, if the radius of BMP is known. To the best of our knowledge, so far the static dielectric constant of magnetic semiconductors with BMP has not been determined from modelled impedance data. In the project we developed metal-semiconductor-insulator-semiconductur (MSIS) structures which are suitable for impedance measurements and for extraction of the static dielectric constant of ZnO from the modelled impedance data. We measured and modelled the room temperature impedance of metal/(ZnO or ZnMnO or ZnCoO)/insulator/semiconductor (MSIS) capacitive structures and modelled the static dielectric constant of ZnO, ZnMnO, and ZnCoO. We confirmed the dielectric constant of ZnO (εr=8.64…9.97). We consider the observed increase of static dielectric constant εr in ZnMnO and in ZnCoO, namely εr=27.00 in ZnMnO with 5 at.% Mn, εr=33.87 in ZnMnO with 2 at.% Mn, εr=18.11 in ZnCoO with 5 at.% Co, and εr=22.01 in ZnCoO with 2 at.% Co as one key result of the project. We expect that our equivalent circuit model which includes defects in the magnetic semiconductor material is versatile enough to be used by scientists who wish to extract the static dielectric constant from the measured impedance data on MSIS structures with other magnetic semiconductors. Scientist being interested in the static dielectric constant of magnetic semiconductors with BMP may be encouraged to prepare comparable MSIS structures suitable for impedance measurements. Furthermore, in order to understand the temperature dependent magnetoconductance in magnetic ZnO, it is necessary to classify the samples into 2D samples, 3D samples, and 2D+3D samples. In the project we have measured and modeled the temperature dependent magnetoconductance in ZnCoO and ZnMnO thin films with nominal concentrations of 5 at. %, 2 at. % and 0.1 at. %. We observed a temperature dependent anisotropy of interaction and localization effects as independent phenomena in magnetic ZnO. The modelling with the temperature dependence (LTh~T-0.5) for conducting surface is in good agreement with the Thouless diffusion length (LTh) proposed by the Nobel Prize winners David J. Thouless and J. Michael Kosterlitz in the 70s to describe transport in ultrathin films in the unordered phase. We believe that our work is of interest to scientists working in the research field of low temperature magnetoconductance of surface conducting semiconductors with the focus on the control of magnetoconductance by substitutional magnetic ions. We developed a concept for novel magnetooptical sensors based on ZnO coated Si3N4 MIS structures with similar photocapacitive functionality as the BFO coated Si3N4 MIS structure to detect intensity and color of visible light by impedance measurements. We suggest to use the ZnO coated Si3N4 MIS capacitor as magneto-capacitive detector where the presence of a magnetic field can be detected via the increase of static dielectric constant due to the formation of BMPs with aligned spins of magnetic ions. We developed a concept for novel large field magnetoresistance sensors based on magnetic ZnO thin films with tunable magnetoconductivity carried by a parallel combination of 2D layer conductance and 3D layer conductance in dependence on the species and concentration of magnetic ions in magnetic ZnO which are expected to reveal a linear magnetoresistance in a defined magnetic field range at the working temperature.
Publications
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Capacitance of Si3N4 /p-Si MIS structures in dependence on contact area and interface defects, TU Chemnitz, Aug. 2018
Vinayak Jayram Bhat
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Probing defect driven tunable spontaneous magnetization in paramagnetic Zn0.95Co0.05O epitaxial films by X-ray absorption investigations, JALCOM 649, 891-898 (2015)
P. Satyarthi, S. Ghosh, Y.T. Wang, S. Zhou, P. Kumar, D. Kanjilal, L. Olivi, D. Bürger, I. Skorupa, H. Schmidt, P. Srivastava
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Direct evidence of defect coordination and magnetic interaction in local structure of wurtzite type Zn1-xCoxO thin films, JALCOM 670, 113-122 (2016)
P. Satyarthi, S. Ghosh, Y. Wang, S. Zhou, D. Bürger, I. Skorupa, H. Schmidt, L. Olivi, P. Srivastava,
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Unraveling carrier’s kinetics in tuning the ferromagnetism of transparent Zn0.95Co0.05O epitaxial films, Journal of Alloys and Compounds 687, 28- 36 (2016)
P. Satyarthi, S. Ghosh, B.R. Sekhar, Y. Wang, S. Zhou, I. Skorupa, D. Bürger, H. Schmidt, P. Srivastava
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Thouless length and valley degeneracy factor of ZnMnO thin films with anisotropic, highly conductive surface layers, J. Appl. Phys. 121, 225105 (2017)
S. V. Vegesna, D. Bürger, R. Patra, B. Abendroth, I. Skorupa, O.G. Schmidt, H. Schmidt
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Tunable large field magnetoconductance of ZnO, ZnMnO, and ZnCoO thin films, J. Appl. Phys. 125, 215305 (2019)
S.V. Vegesna, D. Bürger, R. Patra, J. Dellith, B. Abendroth, I. Skorupa, O.G. Schmidt, H. Schmidt
