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Observation of the Onset of Magnetic Clustering in Superparamagnetic Zn1−x Co x O Films

  • S. Ye
  • V. Ney
  • T. Kammermeier
  • K. Ollefs
  • A. Ney
  • F. Wilhelm
  • A. Rogalev
Original Paper
  • 52 Downloads

Abstract

A series of high quality Zn1−x Co x O thin films were obtained by UHV-magnetron reactive sputtering. Detailed X-ray diffraction, X-ray absorption near edge spectra, and X-ray linear dichroism measurements were used for analyzing the long- and short-range crystalline structure, respectively. These techniques reveal excellent crystalline ordering on both scales for films with oxygen-rich conditions and indicate that Co2+ ions are located on substitutional Zn sites without detectable phase separation. Interestingly, decreasing the structural quality of such Zn1−x Co x O films leads to altered magnetic properties as measured by SQUID magnetometry, ranging from paramagnetism to the emergence of magnetic clustering exhibited by superparamagnetism. In some cases, a small shift of the hysteresis loop is visible after field cooling indicating weak exchange bias typical for the AFM/FM (CoO/Co) system. In the light of detailed structural investigations, the transition regime from paramagnetic to superparamagnetic behavior is discussed.

Keywords

Zn1−xCoxO thin films XRD XANES XLD 

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Copyright information

© Springer Science+Business Media, LLC 2009

Authors and Affiliations

  • S. Ye
    • 1
    • 2
  • V. Ney
    • 1
  • T. Kammermeier
    • 1
  • K. Ollefs
    • 1
  • A. Ney
    • 1
  • F. Wilhelm
    • 3
  • A. Rogalev
    • 3
  1. 1.ExperimentalphysikUniversität Duisburg-EssenDuisburgGermany
  2. 2.Institute of Microelectronics and Information TechnologyWuhan UniversityWuhanChina
  3. 3.European Synchrotron Radiation Facility (ESRF)Grenoble CedexFrance

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