Growth of ZnO:Mn/ZnO:V Heterostructures and Ferroelectric-ferromagnetic Characterization
- PDF / 350,860 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 75 Downloads / 375 Views
1161-I02-02
Growth of ZnO:Mn/ZnO:V Heterostructures and Ferroelectric-ferromagnetic Characterization Devajyoti Mukherjee, Tara Dhakal, Hariharan Srikanth, Pritish Mukherjee and Sarath Witanachchi Department of Physics, University of South Florida, Tampa, Florida. ABSTRACT The wide band gap semiconductor ZnO is well known for its multifunctionality in the form of ferromagnetism (FM), piezoelectricity, and magneto optics. ZnO has been found to grow with intrinsic oxygen deficiencies which in turn are believed to give ferromagnetism and high conductivity in this material. Doping Zn2+ sites by V5+ ions creates a mixed valency as well as strain in the original ZnO hexagonal structure because of the reduced ionic size of vanadium. The mixed valency creates charge polarity between Zn-O and V-O bonds. This charge polarity and the rotation of the nonlinear V-O bonds with respect to Zn-O bonds under electric field have been shown to produce ferroelectricity. Furthermore, Mn doping of ZnO has also shown enhancement in ferromagnetic properties in ZnO. For this material to be a viable ferromagnetic material the magnetic properties should not be from segregated phases. In the present study we have grown undoped, Mn, and V doped ZnO thin films using pulsed laser deposition (PLD). ZnO target with 2% atomic Mn doping and a target with 0.5% atomic V doping were prepared by solid state reactions and sintering. Films were grown both epitaxially on sapphire substrates and in polycrystalline form on silicon substrates. Magnetization measurements by the PPMS showed M vs. H hysteresis loops with saturation for all ZnO: Mn films. V doped films showed high saturation polarization for film deposited at high pressures. We have also fabricated epitaxial bilayers of ZnO:V/ZnO:Mn on sapphire substrates. Ferroelectric and ferromagnetic properties of these heterostructures are presented. INTRODUCTION Room temperature ferromagnetism seen in ZnO is attributed to the intrinsic oxygen deficiency. Recently, some studies have also revealed the introduction of a strong magnetic moment to ZnO by doping with Mn [1]. Zn1 – xMnxO has attracted more attentions because of the wide band gap of ZnO and the high thermal solubility of Mn in ZnO. Theoretically Mn doped ZnO is predicted to have the critical temperature (Tc) well above room temperature [2]. Mn when doped nominally in ZnO is found to be in Mn2+ oxidation state and the ferromagnetism is carrier induced for Mn concentrations below 5 at.% [3]. In contrast to the ref. 3, Kundaliya et al. [4] have claimed that the ferromagnetism in Mn:ZnO system is due to the metastable phase (Mn2O3) rather than by the carrier induced interaction among substituted Mn ions in ZnO. Our analysis shows that the ferromagnetism shown at epitaxial Mn doped ZnO induced from carrier induced interaction and can be explained by using RKKY interaction. Vanadium (V) doped ZnO has been shown to be ferroelectric [5]. Our goal was to find the growth conditions to maximize the magnetic moment in Mn doped ZnO and investigate the multiferroi
Data Loading...
