Magnetic phase diagram of transition metal doped ZnO from density functional theory calculations and Monte Carlo simulat
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Magnetic phase diagram of transition metal doped ZnO from density functional theory calculations and Monte Carlo simulations Sanjeev K. Nayak1, Heike C. Herper1 and Peter Entel1 1 Faculty of Physics, University of Duisburg-Essen, Lothar Str. 1, 47057 Duisburg, Germany ABSTRACT Transition metals doped ZnO are possible candidates for multiferroics. Here, we have investigated the evolution of ferromagnetism due to Co dopants. The magnetic properties have been studied for Co concentrations from 0 to 100% by using ab-initio methods, i.e., KKR Green’s function techniques. In order to estimate the Curie temperature we have performed Monte Carlo simulations with ab-initio calculated exchange parameters. From our calculations the onset of ferromagnetism occurs between 5 to 20% of Co depending on the numerical details of KKR method used. For Co concentrations larger than 50% the system is dominated by antiferromagnetic coupling and no Curie temperature can be obtained. INTRODUCTION ZnO is one of the most demanding materials for various applications. In normal conditions it stabilizes in wurtzite crystal structure (P63mc crystal symmetry), which is a relatively open structure and shows a rich defect chemistry. Some of the defects occur naturally in the system, like the hydrogen diffusion, thus rendering n-type semiconducting character. Other possible vacancies, like Zn interstitial and O vacancies are discussed with respect to several properties of pure ZnO. As one reduces the dimension from bulk to thin films or to nanoparticles, the influence of surfaces and interfaces cannot be neglected. In addition, intentional doping of various elements will give rise to a spectrum of physical properties to ZnO. ZnO is a suitable material for optical and electronic devices. Since the wurtzite cluster lacks inversion symmetry, these semiconductors show piezoelectric properties. In addition, if the magnetic properties could be stabilized with transition metal (TM), they can lead to multi-ferroic materials, which for ZnO is already being attempted [1,2]. In this contribution we report our studies on the magnetic properties of ZnO as a diluted magnetic semiconductor (DMS) with the Co dopant. While the DMS has been studied for long, it is only since the prediction of Dietl et al. [3] that there has been surge in search for magnetic properties in various semiconductors. Dietl et al. carried out mean-field calcuations and showed that some of the ionic semiconductors like ZnO and GaN could be ferromagnetic above room temperature (RT) when doped with Mn and large hole concentration. Both RT ferromagnetism and p-type material is still under much discussion. The literature is presently rich in reports of magnetic properties, not only with TM and rare earth doping, but also with other sp-elements , which is mostly categorized into sp-magnetism or d0-magnetism. With respect to TM doped ZnO, there are concerns about the possible origin of magnetic interaction, because the reports of ferromagnetism are counteracted by other research findin
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