Semiconducting and ferromagnetic behavior of sputtered Co-doped TiO2 thin films above room temperature
13 May 2002-Journal of Applied Physics (American Institute of Physics)-Vol. 91, Iss: 10, pp 8093-8095
TL;DR: In this paper, the authors investigated Co-doped TiO2 thin films grown by reactive co-sputtering and found a single phase polycrystalline rutile structure, without any segregation of Co into particulates within the instrumental resolution limit.
Abstract: We have investigated Co-doped TiO2 thin films grown by reactive co-sputtering. X-ray diffraction showed a single phase polycrystalline rutile structure, without any segregation of Co into particulates within the instrumental resolution limit. The atomic content of Co ranged from 1% to 12%. The temperature dependence of resistivity showed an extrinsic semiconducting behavior. From optical absorption measurements, the band gap Eg≈3.25±0.05 eV was found, independent of the Co concentration, and in agreement with a literature value. Room temperature M-H loops showed a ferromagnetic behavior for Co content higher than 3%. The magnetic moment per Co atom was estimated to be about 0.94 μB, suggesting a low spin configuration of Co ions. The temperature dependence of remanent magnetization revealed a Curie temperature higher than 400 K for Co content of 12%.
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TL;DR: A review of recent results on transition metal doping of electronic oxides such as ZnO, TiO 2, SnO2, BaTiO 3, Cu2O, SrTiO3 and KTaO3 is presented in this article.
Abstract: A review of recent results on transition metal doping of electronic oxides such as ZnO, TiO2, SnO2, BaTiO3, Cu2O, SrTiO3 and KTaO3 is presented. There is interest in achieving ferromagnetism with Curie temperatures above room temperature in such materials for applications in the field of spintronic devices, in which the spin of the carriers is exploited. The incorporation of several atomic per cent of the transition metals without creation of second phases appears possible under optimized synthesis conditions, leading to ferromagnetism. Pulsed laser deposition, reactive sputtering, molecular beam epitaxy and ion implantation have all been used to produce the oxide-based dilute magnetic materials. The mechanism is still under debate, with carrier-induced, double-exchange and bound magnetic polaron formation all potentially playing a role depending on the conductivity type and level in the material.
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TL;DR: In this paper, the authors summarize the current status of oxide-based diluted magnetic semiconductors, and discuss the influence of growth method, substrate choice, and temperature on the microstructure and subsequent magnetic properties of thin films.
Abstract: There has been considerable recent interest in the design of diluted magnetic semiconductors, with a particular focus on the exploration of different semiconductor hosts. Among these, the oxide-based diluted magnetic semiconductors are attracting increasing attention, following reports of room temperature ferromagnetism in anatase TiO2 and wurtzite ZnO doped with a range of transition metal ions. In this review we summarize the current status of oxide-based diluted magnetic semiconductors, and discuss the influence of growth method, substrate choice, and temperature on the microstructure and subsequent magnetic properties of thin films. We outline the experimental conditions that promote large magnetization and high ferromagnetic Curie temperature. Finally, we review the proposed mechanisms for the experimentally observed ferromagnetism and compare the predictions to the range of available data.
489 citations
TL;DR: The experimental status of O-DMS including the recent results on ZnO-and TiO2-based systems is described in this paper, where the authors present a review of the experimental status and experimental results on O-diluted magnetic semiconductors.
Abstract: Oxide-diluted magnetic semiconductors (O-DMS) have attracted a great deal of interest in recent years due to the possibility of inducing room temperature ferromagnetism These materials are of particular interest for spintronic devices such as spin valves This review describes the experimental status of the O-DMS including the recent results on ZnO- and TiO2-based systems
381 citations
Journal Article•
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TL;DR: In this paper, the most important results on oxide spintronics were reviewed, emphasizing materials physics as well as spin-dependent transport phenomena, and finally give some perspectives on how the flurry of new magnetic oxides could be useful for next-generation spintronic devices.
Abstract: Concomitant with the development of metal-based spintronics in the late 1980s and 1990s, important advances were made on the growth of high-quality oxide thin films and heterostructures. While this was at first motivated by the discovery of high-temperature superconductivity in perovskite Cu oxides, this technological breakthrough was soon applied to other transition-metal oxides and, notably, mixed-valence manganites. The discovery of colossal magnetoresistance in manganite films triggered intense research activity on these materials, but the first notable impact of magnetic oxides in the field of spintronics was the use of such manganites as electrodes in magnetic tunnel junctions, yielding tunnel magnetoresistance ratios that are one order of magnitude larger than what had been obtained with transition-metal electrodes. Since then, research on oxide spintronics has been intense, with the latest developments focused on diluted magnetic oxides and, more recently, on multiferroics. In this paper, the most important results on oxide spintronics was reviewed, emphasizing materials physics as well as spin-dependent transport phenomena, and finally give some perspectives on how the flurry of new magnetic oxides could be useful for next-generation spintronics devices
301 citations
Cites background from "Semiconducting and ferromagnetic be..."
...A ferromagnetic behavior was also found for sputtered Co-doped anatase TiO2 films [214] and in Co-doped rutile TiO2 [215]....
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TL;DR: In this article, the structural, optical, and magnetic properties of chemically synthesized pure and Co-doped powders using x-ray diffraction (XRD), diffuse reflectance spectroscopy (DSS) and magnetometry were investigated.
Abstract: In this paper, we present the results of a detailed investigation of the structural, optical, and magnetic properties of chemically synthesized pure and Co-doped $\mathrm{Sn}{\mathrm{O}}_{2}$ powders using x-ray diffraction (XRD), diffuse reflectance spectroscopy, Raman spectroscopy, x-ray photoelectron spectroscopy, and magnetometry. In ${\mathrm{Sn}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{\mathrm{O}}_{2}$ samples prepared at $600\phantom{\rule{0.2em}{0ex}}\ifmmode^\circ\else\textdegree\fi{}\mathrm{C}$ with low doping concentrations of Co $(\ensuremath{\leqslant}1%)$, the $\mathrm{Sn}{\mathrm{O}}_{2}$ lattice contracts, band gap energy decreases, and a ferromagnetic behavior is developed. Increasing the Co doping concentration to $g1%$ leads to a rapid expansion of the lattice and significant structural disorder evidenced by changes in the XRD and Raman spectra presumably due to additional interstitial incorporation of Co. This higher Co doping completely destroys the ferromagnetism. The striking similarity between the changes in the lattice parameters and the magnetic properties of ${\mathrm{Sn}}_{1\ensuremath{-}x}{\mathrm{Co}}_{x}{\mathrm{O}}_{2}$ indicates a structure-magnetic property relationship.
245 citations
References
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TL;DR: Zener's model of ferromagnetism, originally proposed for transition metals in 1950, can explain T(C) of Ga(1-)(x)Mn(x)As and that of its II-VI counterpart Zn(1)-Mn (x)Te and is used to predict materials with T (C) exceeding room temperature, an important step toward semiconductor electronics that use both charge and spin.
Abstract: Ferromagnetism in manganese compound semiconductors not only opens prospects for tailoring magnetic and spin-related phenomena in semiconductors with a precision specific to III-V compounds but also addresses a question about the origin of the magnetic interactions that lead to a Curie temperature (T(C)) as high as 110 K for a manganese concentration of just 5%. Zener's model of ferromagnetism, originally proposed for transition metals in 1950, can explain T(C) of Ga(1-)(x)Mn(x)As and that of its II-VI counterpart Zn(1-)(x)Mn(x)Te and is used to predict materials with T(C) exceeding room temperature, an important step toward semiconductor electronics that use both charge and spin.
7,062 citations
TL;DR: The magnetic coupling in all semiconductor ferromagnetic/nonmagnetic layered structures, together with the possibility of spin filtering in RTDs, shows the potential of the present material system for exploring new physics and for developing new functionality toward future electronics.
Abstract: REVIEW Semiconductor devices generally take advantage of the charge of electrons, whereas magnetic materials are used for recording information involving electron spin. To make use of both charge and spin of electrons in semiconductors, a high concentration of magnetic elements can be introduced in nonmagnetic III-V semiconductors currently in use for devices. Low solubility of magnetic elements was overcome by low-temperature nonequilibrium molecular beam epitaxial growth, and ferromagnetic (Ga,Mn)As was realized. Magnetotransport measurements revealed that the magnetic transition temperature can be as high as 110 kelvin. The origin of the ferromagnetic interaction is discussed. Multilayer heterostructures including resonant tunneling diodes (RTDs) have also successfully been fabricated. The magnetic coupling between two ferromagnetic (Ga,Mn)As films separated by a nonmagnetic layer indicated the critical role of the holes in the magnetic coupling. The magnetic coupling in all semiconductor ferromagnetic/nonmagnetic layered structures, together with the possibility of spin filtering in RTDs, shows the potential of the present material system for exploring new physics and for developing new functionality toward future electronics.
4,339 citations
TL;DR: The observation of transparent ferromagnetism in cobalt-doped anatase thin films with the concentration of cobalt between 0 and 8% is reported, indicating the existence of ferromagnetic long-range ordering.
Abstract: Dilute magnetic semiconductors and wide gap oxide semiconductors are appealing materials for magnetooptical devices. From a combinatorial screening approach looking at the solid solubility of transition metals in titanium dioxides and of their magnetic properties, we report on the observation of transparent ferromagnetism in cobalt-doped anatase thin films with the concentration of cobalt between 0 and 8%. Magnetic microscopy images reveal a magnetic domain structure in the films, indicating the existence of ferromagnetic long-range ordering. The materials remain ferromagnetic above room temperature with a magnetic moment of 0.32 Bohr magnetons per cobalt atom. The film is conductive and exhibits a positive magnetoresistance of 60% at 2 kelvin.
2,302 citations
TL;DR: In this paper, the authors reported the fabrication of all-semiconductor, light-emitting spintronic devices using III-V heterostructures based on gallium arsenide.
Abstract: Conventional electronics is based on the manipulation of electronic charge. An intriguing alternative is the field of ‘spintronics’, wherein the classical manipulation of electronic spin in semiconductor devices gives rise to the possibility of reading and writing non-volatile information through magnetism1,2. Moreover, the ability to preserve coherent spin states in conventional semiconductors3 and quantum dots4 may eventually enable quantum computing in the solid state5,6. Recent studies have shown that optically excited electron spins can retain their coherence over distances exceeding 100 micrometres (ref. 7). But to inject spin-polarized carriers electrically remains a formidable challenge8,9. Here we report the fabrication of all-semiconductor, light-emitting spintronic devices using III–V heterostructures based on gallium arsenide. Electrical spin injection into a non-magnetic semiconductor is achieved (in zero magnetic field) using a p-type ferromagnetic semiconductor10 as the spin polarizer. Spin polarization of the injected holes is determined directly from the polarization of the emitted electroluminescence following the recombination of the holes with the injected (unpolarized) electrons.
2,197 citations
TL;DR: In this article, a new GaAs-based diluted magnetic semiconductor, (Ga,Mn)As, was prepared by molecular beam epitaxy and the lattice constant was determined by x-ray diffraction and shown to increase with the increase of Mn composition, x.
Abstract: A new GaAs‐based diluted magnetic semiconductor, (Ga,Mn)As, was prepared by molecular beam epitaxy. The lattice constant of (Ga,Mn)As films was determined by x‐ray diffraction and shown to increase with the increase of Mn composition, x. Well‐aligned in‐plane ferromagnetic order was observed by magnetization measurements. Magnetotransport measurements revealed the occurrence of anomalous Hall effect in the (Ga,Mn)As layer.
2,072 citations