Ion irradiation as a controllable approach to study the defect-induced ferromagnetism


Ion irradiation as a controllable approach to study the defect-induced ferromagnetism

Zhou, S.; Potzger, K.; Yang, Z.; Helm, M.; Fassbender, J.

Recently, ferromagnetism was observed in nonmagnetically doped, but defective semiconductors or insulators, including TiO2 [1] and ZnO [2-5] (see a review by Coey et al. [6]). This kind of observation challenges the conventional understanding of ferromagnetism, which is rather due to spin-split states or bands. Often the defect-induced ferromagnetism has been observed in samples prepared under non-optimized condition, i.e. by accidence or by mistake. To understand the mechanism of the defect-induced ferromagnetism, one needs a better controlled method to create defects in the crystalline materials. As a nonequilibrium and reproducible approach of inducing defects, ion irradiation provides such a possibility. Energetic ions displace atoms from their equilibrium lattice sites, thus creating mainly vacancies, interstitials or antisites. The amount and the distribution of defects can be controlled by the ion fluence and energy. By ion irradiation, we have generated defect-induced ferromagnetism in TiO2 [1] and SiC [7]. The saturation magnetization rises and falls with increasing the ion fluence due to the interplay between the amount of defects and the crystalline quality. Using electron spin resonance and positron annihilation spectroscopies, one can determine where the unpaired electrons are located and the concentration of defects. Ion irradiation combined with proper characterizations of defects could allow us to clarify the local magnetic moments and the coupling mechanism in defective semiconductors. Otherwise we may have to build a new paradigm to understand the defect-induced ferromagnetism.

Reference:

[1] S. Zhou, et al., Phys. Rev. B 79, 113201 (2009).
[2] S. Zhou, et al., J. Phys. D 41, 105011 (2008).
[3] K. Potzger, et al., Appl. Phys. Lett. 92, 182504 (2008).
[4] S. Zhou, et al., Appl. Phys. Lett. 93, 232507 (2008).
[5] Q. Xu, et al., Appl. Phys. Lett. 92, 082508 (2008).
[6] J. M. D. Coey, et al., New J. Phys. 12, 053025 (2010).
[7] L. Li, et al., Appl. Phys. Lett. 98, 222508 (2011).

Related publications

  • Invited lecture (Conferences)
    China-Germany Symposium on "Electronic structure calculations and their application in material science", 08.-11.11.2011, Chengdu, China
  • Poster
    The 56th Magnetism and Magnetic Materials Conference, 30.10.-03.11.2011, Phoenix / Scottsdale, USA
  • Invited lecture (Conferences)
    Invited seminar at the Institute of Solid State Physics, Chinese Academy of Sciences, 13.10.2011, Hefei, China

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