Eur. Phys. J. B 79, 185-195 (2011)
https://doi.org/10.1140/epjb/e2010-10512-3

Magnetic and transport properties of transition-metal implanted ZnO single crystals

¹ Centro de Física da Matéria Condensada da Universidade de Lisboa, Campo Grande, Ed. C8, 1749-016 Lisboa, Portugal
² Laboratório de Feixe de Iões, Dep. Física, Instituto Tecnológico e Nuclear, Estrada Nacional 10, 2686-953 Sacavém, Portugal
³ Centro de Física Nuclear da Universidade de Lisboa, Av. Prof. Gama Pinto 2, 1649-003 Lisboa, Portugal
⁴ Departamento de Física, Faculdade de Ciências, Universidade de Lisboa, Campo Grande, Ed. C8, 1749-016 Lisboa, Portugal
⁵ Instituto Tecnológico e Nuclear, Departamento de Química, 2686-953 Sacavém, Portugal

Corresponding author: ^a rpborges@fc.ul.pt

Received: 30 June 2010
Revised: 19 November 2010
Published online: 23 December 2010

Abstract

ZnO single crystals were implanted with Mn, Co and Ni with fluences between 1 × 10¹⁶ cm^-2 and 1 × 10¹⁷ cm^-2 and energy of 200 keV. Results indicate that aggregation of transition metal ions in the as implanted state occurs only in the case of Ni. After an annealing stage to recover the ZnO structure aggregation occurs for the higher fluences of all implanted species. For lower concentrations paramagnetic behaviour with magnetic moments close to those of individual ions is observed. No polarised impurity band is formed as a result of the presence of transition metal ions and all samples show electrical conduction by carriers in extended states of ZnO. Significant values of magnetoresistance are measured at low temperatures, where electrical transport is described by hopping mechanisms between localized states. The sign of the magnetoresistance is dependent of the doping ion and is correlated with the observed aggregation.