A comparison between ZnO films doped with 3d and 4f magnetic ions Mariana Ungureanu a, ⁎ , Heidemarie Schmidt a , Holger von Wenckstern a , Holger Hochmuth a , Michael Lorenz a , Marius Grundmann a , Marian Fecioru-Morariu b , Gernot Güntherodt b a Universität Leipzig, Institut für Experimentelle Physik II, Abteilung Halbleiterphysik, Linnestrasse 5, 04103 Leipzig, Germany b II. Physikalisches Institut, RWTH Aachen, Physikzentrum Melaten, Huyskensweg Turm 28B, 52074 Aachen, Germany Available online 6 April 2007 Abstract We present electrical and magnetic properties of ZnO films doped with 3d (Mn) and 4f (Gd or Nd) magnetic ions grown on a-plane Al 2 O 3 substrates. Both for films doped with 3d magnetic ions and for films doped with 4f magnetic ions, Hall investigations revealed that the carrier concentration decreases and the resistivity increases with increasing the oxygen partial pressure during the pulsed laser deposition growth, probably because the formation of oxygen vacancies is hindered. Measurements of magnetic properties revealed ferromagnetism above room temperature with magnetic moments up to 0.2 μ B /Mn ion in insulating ZnO:Mn films co-doped with 0.1% P and up to 0.3 μ B /Gd ion in n- conducting ZnO:Gd films co-doped with 0.2% Al. © 2007 Elsevier B.V. All rights reserved. Keywords: Diluted magnetic semiconductors; ZnO 1. Introduction The field of spintronics is based on the idea to use the electron spin rather than, or in addition to charge for new electronic devices [1]. Diluted magnetic semiconductors (DMS), systems formed by substituting a fraction of a host semiconductor cations with magnetic ions, are believed to be suited materials for spintronics applications. We chose ZnO as semiconductor host because is widely used in electronic devices, for example in gas sensors, transparent conducting layers and green or white light-emitting devices, due to its wide band gap of 3.3 eV. A DMS that could find practical applications should be ferromagnetic above room temperature. Theoretical computations predicted that transition metal (TM) ions substituted in ZnO could produce ferromagnetism above 300 K [2–4]. Experimentally, ferromagnetism was obtained above 300 K with small magnetic moments for 3d-TM in ZnO [5,6]. An approach to use rare earth (RE) elements as doping magnetic ions in the GaN host, produced large magnetic moments and ferromagnetism above room temperature [7]. In this paper we present structural, electrical and magnetic properties of ZnO films doped with 3d-TM (Mn) or 4f-RE (Gd, Nd) magnetic ions grown by pulsed laser deposition (PLD) on a-plane Al 2 O 3 substrates. Our work indicated alike behaviors in ZnO:Gd films and ZnO:Nd films, for this reason in the remainder of this paper we will make no distinction between these materials. Hall investigations revealed that the carrier concentration decreases and the resistivity increases with increasing the oxygen partial pressure during the PLD growth, probably because the formation of oxygen vacancies is hindered [8]. Magnetic behavior of films was studied in a superconducting quantum interference device (SQUID) magnetometer and revealed ferromagnetic behavior above 300 K in insulating ZnO:Mn and ZnO:(Mn, P) films with around 5% Mn and in n- conducting ZnO:(Gd, Al) films with around 1% Gd. 2. Film growth and structural properties We prepared and analyzed ZnO films doped with 3% and 5% Mn or with 0.1% and 1% Gd or Nd. We used the PLD technique to grow films with thickness from 20 nm to 1 μm on a-plane Al 2 O 3 substrates. The PLD growth temperature was varied between 450 and 850 °C. The films were grown in O 2 or N 2 atmosphere at pressures between 2E-5 and 0.3 mbar. A part of the films containing Mn were co-doped with 0.1% and 0.5% P or 0.05% Sn in order to investigate if their magnetic properties Thin Solid Films 515 (2007) 8761 – 8763 www.elsevier.com/locate/tsf ⁎ Corresponding author. Tel.: +49 341 97 32666; fax: +49 341 9732668. E-mail address: ungureanu_mary@yahoo.de (M. Ungureanu). 0040-6090/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.tsf.2007.04.010