First principles materials design for semiconductor spintronics

Satō, Kazunori; Katayama‐Yoshida, Hiroshi

doi:10.1088/0268-1242/17/4/309

Cited by 825 publications

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“…The ultimate aim is a controllable room temperature semiconducting ferromagnet, which could be used in magnetoelectric and magnetotransport devices. Intrinsically magnetic semiconductors generally possess relatively low Curie temperatures (T C ); however, it has been proposed that incorporating transition metal or rare earth ions into a nonmagnetic semiconductor host lattice, forming a dilute magnetic semiconductor (DMS), may help raise T C above room temperature [2,3].In DMS materials, magnetism is influenced and controlled by the presence of charge carriers in the form of holes (GaAs:Mn) or electrons (GaN:Gd). There is still great debate over the fundamental mechanism behind the origin of the observed high temperature magnetic alignment in many of these systems.…”

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Theoretical Description of Carrier Mediated Magnetism in Cobalt Doped ZnO

2008

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Substitutional cobalt in ZnO has a weak preference for antiferromagnetic ordering. Stabilization of ferromagnetism is achieved through n-type doping, which can be understood through a band coupling model. However, the description of the transition to a ferromagnetic ground state varies within different levels of band theory; issues arise due to the density functional theory underestimation of the band gap of ZnO, and the relative position of the nominally unfilled Co t 2d states. We examine these limitations, including approaches to overcome them, and explain the contradictions in previous studies, which drastically overestimate the doping threshold for magnetic ordering. DOI: 10.1103/PhysRevLett.100.256401 PACS numbers: 71.20.Nr, 71.15.Mb, 75.10.ÿb, 75.50.Pp The potential to simultaneously tune both charge and spin in solid state materials has lead to great interest in the field of spintronics [1]. The ultimate aim is a controllable room temperature semiconducting ferromagnet, which could be used in magnetoelectric and magnetotransport devices. Intrinsically magnetic semiconductors generally possess relatively low Curie temperatures (T C ); however, it has been proposed that incorporating transition metal or rare earth ions into a nonmagnetic semiconductor host lattice, forming a dilute magnetic semiconductor (DMS), may help raise T C above room temperature [2,3].In DMS materials, magnetism is influenced and controlled by the presence of charge carriers in the form of holes (GaAs:Mn) or electrons (GaN:Gd). There is still great debate over the fundamental mechanism behind the origin of the observed high temperature magnetic alignment in many of these systems. The situation is not helped by large variation in both experimental and theoretical studies [4 -8].Cobalt doped ZnO has become a focus of attention due to its reported high T C of up to 700 K and, most promisingly, the reversible cycling of FM ordering [9]. Coupled with existing optical and electrical properties of ZnO, the addition of controllable magnetism could make it a technologically essential material. It has been reported that at Co concentrations of less than 10%, the solubility is good and Co occupies a substitutional Zn site in a 2 charge state [9,10]. B . The splitting between filled e d and empty minority t 2d states for tetrahedral Co is typically on the order of 1.5-2 eV [12]. In a wide gap semiconductor such as ZnO (E g 3:4 eV), this would place the minority spin Co t 2d states within the band gap, as has been reported from both optical and magnetic measurements for ZnO:Co [13][14][15]. Surprisingly, this is not the case in previous theoretical studies [5][6][7][8].From consideration of Co 3d band coupling, FM interactions between occupied majority t 2d states results in no net energy gain due to filled bonding and antibonding combinations, while AFM interactions can result in a small energy gain (Fig. 1). Partial occupation of the empty minority t 2d states will result in a transition to FM ordering through the energy gained from the fi...

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Theoretical Description of Carrier Mediated Magnetism in Cobalt Doped ZnO

2008

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“…[15] In general, studies on polycrystalline samples have converged on to a conclusion that robust room temperature ferromagnetism (RTF) is not realizable in Co doped ZnO without additional carrier doping. Sato and Katayama-Yoshida [16] predicted Co doped ZnO would become ferromagnetic in the presence of n-type carriers. This was experimentally demonstrated by Schwartz and Gamelin.…”

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Surfactant‐Assisted Synthesis of Co‐ and Li‐Doped ZnO Nanocrystalline Samples Showing Room‐Temperature Ferromagnetism

2006

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The dilute magnetic semiconductor oxides (DMSO) are of current interest because of their potential 'spintronics' applications, where the charge and spin degrees of freedom of electrons are used simultaneously for novel memory and optical device applications. [1,2] In particular, Co doped ZnO has attracted considerable interest. [3] There have been a number of reports about the observance of room temperature ferromagnetism in thin films of Zn 1-x Co x O produced by different techniques. [4][5][6][7] Schwartz et al. [8] also observed ferromagnetism above room temperature in aggregated particles of Co doped ZnO, by heat treating (below 200 o C) colloidal quantum dots of Co doped ZnO. However, most recent works on well-characterized polycrystalline Zn 1-x Co x O samples indicate that they are not ferromagnetic at room temperature, [9][10][11][12][13][14] except for an isolated report by Deka et al.. [15] In general, studies on polycrystalline samples have converged on to a conclusion that robust room temperature ferromagnetism (RTF) is not realizable in Co doped ZnO without additional carrier doping. Sato and Katayama-Yoshida [16] predicted Co doped ZnO would become ferromagnetic in the presence of n-type carriers. This was experimentally demonstrated by Schwartz and Gamelin. [17] They were the first to show the reversible cycling of paramagnetic (P) to ferromagnetic (FM) state in Co doped ZnO spin coated films, produced from colloidal nanocrystals, by introducing and removing interstitial Zn (Zn i ), a native n-type defect of ZnO. Later Spaldine, [18] in a computational study, showed only hole doping promotes RTF in Co doped ZnO. This is in contrast with

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“…One class of materials, which are especially promising for applications, are diluted magnetic semiconductors, usually ternary systems of the type III 1-x -TM x -V or II 1-x -TM x -VI, where a 3d transition metal (TM) partly substitutes up to a few per cent of the group III or group II cations. It has been predicted by theory that the III-nitride semiconductors GaN and InN and the II-oxide semiconductor ZnO are suitable hosts to exhibit ferromagnetism close to or above room temperature [2,3]. In the case of ZnO, besides V, Cr, Mn, Co and Ni, Fe should also act as a ferromagnetic dopant [3][4][5].…”

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“…It has been predicted by theory that the III-nitride semiconductors GaN and InN and the II-oxide semiconductor ZnO are suitable hosts to exhibit ferromagnetism close to or above room temperature [2,3]. In the case of ZnO, besides V, Cr, Mn, Co and Ni, Fe should also act as a ferromagnetic dopant [3][4][5]. Several reports on ferromagnetic systems based on ZnO can be found in the literature [1,[6][7][8][9][10][11][12][13][14].…”

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Lattice location and thermal stability of implanted Fe in ZnO

Rita

Wahl

Correia

et al. 2004

Applied Physics Letters

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The emission channeling technique was applied to evaluate the lattice location of implanted 59 Fe in singlecrystalline ZnO. The angular distribution of β − particles emitted by 59 Fe was monitored with a position-sensitive electron detector, following 60-keV low dose (2.0×10 13 cm −2 ) room-temperature implantation of the precursor isotope 59 Numerous technological breakthroughs are envisaged with the use of magnetic semiconductor materials that show a ferromagnetic ordering temperature at or above room temperature, e.g., spin transistors, ultradense nonvolatile memories and optical emitters with polarized output [1]. One class of materials, which are especially promising for applications, are diluted magnetic semiconductors, usually ternary systems of the type III 1-x -TM x -V or II 1-x -TM x -VI, where a 3d transition metal (TM) partly substitutes up to a few per cent of the group III or group II cations. It has been predicted by theory that the III-nitride semiconductors GaN and InN and the II-oxide semiconductor ZnO are suitable hosts to exhibit ferromagnetism close to or above room temperature [2,3]. In the case of ZnO, besides V, Cr, Mn, Co and Ni, Fe should also act as a ferromagnetic dopant [3][4][5]. Several reports on ferromagnetic systems based on ZnO can be found in the literature [1,[6][7][8][9][10][11][12][13][14]. Cases in which no ferromagnetic behavior was observed [7,[15][16][17][18] revealed systematic trends for the various transition metals, doping concentrations, and differences between n-and p-type ZnO, but also conflicting results between different authors. It was thus argued [11,14] that experimental reproducibility needs to be improved. The exact nature of the ferromagnetism also remains unclear [1,8,11,13]; among possible problems are the formation of metallic TM or TM-oxide clusters [9,[12][13][14]17] or magnetism from the substrate on which thin films are deposited [18]. Two recent review papers on the subject concluded that a more precise control of the TM dopant in the oxide and careful structural and microstructural analyses are needed [1,11].Experimentally TM dopants have been introduced both during ZnO powder synthesis [10,14,16] and growth of epitaxial thin films [6][7][8][9]11,15,18]. In addition, ion implantation is also actively being explored for TM doping of ZnO [1,12,13,19]. With respect to implantation, the questions that should be clarified, are: to what extent are TMs incorporated into the proper lattice sites (substituting for Zn atoms), what is the microstructure of substitutional TMs, and what are the optimum annealing conditions.We have partly addressed some of these issues in a previous study on Fe-implanted ZnO [20], which, however, focused on its optical properties. In that case, 56 Fe was implanted at 100 keV up to a fluence of 10 16 cm −2 into ZnO single crystals, followed by Rutherford backscattering spectroscopy (RBS) analysis of the damage and its recovery during thermal annealing. Since Fe in ZnO cannot be detected by RBS, particle-induced X-ray emiss...

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First principles materials design for semiconductor spintronics

Cited by 825 publications

References 32 publications

Theoretical Description of Carrier Mediated Magnetism in Cobalt Doped ZnO

Theoretical Description of Carrier Mediated Magnetism in Cobalt Doped ZnO

Surfactant‐Assisted Synthesis of Co‐ and Li‐Doped ZnO Nanocrystalline Samples Showing Room‐Temperature Ferromagnetism

Lattice location and thermal stability of implanted Fe in ZnO

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