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Semiconductors, which are ferromagnetic at room temperature (RTFM), are strived after as potential multifunctional materials. For ZnO, RTFM has been achieved by heavy doping with 3d transition metals. However, neither the conditions for nor the origin of the magnetism is as yet understood. Here, by implanting ZnO at temperatures of 300–800K with dilute, radioactive Mn+57 ions, decaying to the Fe57m Mössbauer state, we show that, most likely, Fe atoms, located on Zn sites in a high-spin Fe3+ state at ⩽600K with large magnetic moments, are in a magnetically ordered atomic surrounding with ordering temperatures ⪢600K. The formation/annealing of the ordering is proposed to occur/disappear on an atomic scale upon the association/dissociation of complexes of Mn∕Fe probe atoms with the (mobile) Zn vacancies that are created in the implantation process. These results challenge present concepts to model (ferro)magnetic ordering in 3d-metal doped oxides and suggest this role of vacancies in the magnetism to be a rather general phenomenon.

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Document VersionPublisher's PDF, also known as Version of record Link back to DTU Orbit Citation (APA): Larsen, A. N., Goubet, J. J., Mejlholm, P., Christensen, J. S., Fanciulli, M., Gunnlaugsson, H. P., ... Dannefaer, S. (2000). Tin-vacancy acceptor levels in electron-irradiated n-type silicon. Physical Review B Condensed Matter, 62(7), 4535-4544. DOI: 10.1103/PhysRevB.62.4535 Tin-vacancy acceptor levels in electron-irradiated n-type silicon 18 Sn/cm 3 were irradiated with 2-MeV electrons to different doses and subsequently studied by deep level transient spectroscopy, Mössbauer spectroscopy, and positron annihilation. Two tin-vacancy ͑Sn-V͒ levels at E c Ϫ0.214 eV and E c Ϫ0.501 eV have been identified ͑E c denotes the conduction band edge͒. Based on investigations of the temperature dependence of the electron-capture cross sections, the electric-field dependence of the electron emissivity, the anneal temperature, and the defect-introduction rate, it is concluded that these levels are the double and single acceptor levels, respectively, of the Sn-V pair. These conclusions are in agreement with electronic structure calculations carried out using a local spin-density functional theory, incorporating pseudopotentials to eliminate the core electrons, and applied to large H-terminated clusters. Thus, the Sn-V pair in Si has five different charge states corresponding to four levels in the band gap.

Interstitial Fe57m atoms excited in the 14.4 keV Mössbauer state have been created in silicon at 400–800 K as a result of the recoil imparted on these daughter atoms in the β− decay of ion-implanted, substitutional Mn57. Diffusional jumps of the interstitial Fe57m cause a line broadening in their Mössbauer spectra, which is directly proportional to their diffusivity. Thus, the charge-state-dependent diffusivity has been determined in differently doped material.