Unconventional magnetoresistance in ZnO/C multilayers at low temperatures

•(ZnO/C)25 multilayers show signatures of local ferromagnetic order at T≤ 120 K.•At T≤ 20 K, magnetoresistance (MR) changes its sign twice in the range B = 0–20 T.•The MR behaviour is associated with three competing mechanisms. A layer-by-layer sputtering method was used to fabricate nanostructures...

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Bibliographic Details
Published in:Journal of magnetism and magnetic materials 2021-10, Vol.535, p.167963, Article 167963
Main Authors: Fadeev, E.A., Lähderanta, E., Aronzon, B.A., Mekhiya, A.B., Kalinin, Yu.E., Makagonov, V.A., Pankov, S.Yu, Foshin, V.A., Granovsky, A.B.
Format: Article
Language:English
Subjects:
Amorphous carbon
Ferromagnetism
Hopping conduction
Hopping conductivity
Hysteresis
Low temperature
Magnetic fields
Magnetism
Magnetoresistance
Magnetoresistivity
Multilayers
Zeeman effect
Zinc oxide
Zinc oxides
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Summary:•(ZnO/C)25 multilayers show signatures of local ferromagnetic order at T≤ 120 K.•At T≤ 20 K, magnetoresistance (MR) changes its sign twice in the range B = 0–20 T.•The MR behaviour is associated with three competing mechanisms. A layer-by-layer sputtering method was used to fabricate nanostructures (ZnO/C)25 composed of zinc oxide and carbon alternating layers, with a total multilayer thickness of 146 nm and 153 nm. At low temperatures, the multilayers show signatures of local ferromagnetic order: magnetic hysteresis, weak magnetization and the characteristic shape of the thermomagnetic curve. In-plane and out-of-plane magnetoresistance (MR) was measured in a pulsed magnetic field up to 20 T in the temperature range of 15–300 K. At T ⩽ 20 K, MR changed its sign from negative in low magnetic fields to positive in moderate fields, and then back to negative in high magnetic fields. At T ⩾ 80 K, MR was negative in the full range of magnetic fields studied. The unusual MR behavior can be associated with the influence of the Zeeman effect on the Fermi level position in the case of 2D variable hopping conduction along the interfaces, scattering on magnetic heterogeneities and the effect of magnetic blockade.
ISSN:0304-8853
1873-4766
DOI:10.1016/j.jmmm.2021.167963