Oxide-diluted magnetic semiconductors: a review of the experimental status

Prellier, W.; Fouchet, Arnaud; Mercey, B.

doi:10.1088/0953-8984/15/37/r01

Cited by 415 publications

(245 citation statements)

References 58 publications

(166 reference statements)

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“…1,2,3,4,5 To this category belongs certainly (Ga,Fe)N, which is the subject of the present work. While extensive studies have been conducted on (Ga,Mn)N 2,5,6,7 as promising workbench for future applications in spintronics, 8,9 only little is known about the (Ga,Fe)N materials system.…”

Section: Introductionmentioning

confidence: 97%

ParamagneticGaN:Feand ferromagnetic(Ga,Fe)N: The relationship between structural, electronic, and magnetic properties

et al. 2007

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We report on the metalorganic chemical vapor deposition (MOCVD) of GaN:Fe and (Ga,Fe)N layers on c-sapphire substrates and their thorough characterization via high-resolution x-ray diffraction (HRXRD), transmission electron microscopy (TEM), spatially-resolved energy dispersive X-ray spectroscopy (EDS), secondary-ion mass spectroscopy (SIMS), photoluminescence (PL), Hall-effect, electron-paramagnetic resonance (EPR), and magnetometry employing a superconducting quantum interference device (SQUID). A combination of TEM and EDS reveals the presence of coherent nanocrystals presumably FexN with the composition and lattice parameter imposed by the host. From both TEM and SIMS studies, it is stated that the density of nanocrystals and, thus the Fe concentration increases towards the surface. According to Hall effect measurements, electrons from residual donors are trapped by mid-gap Fe acceptor states in the limit of low iron content x 0.4%, indicating that the concentration of Fe 2+ ions increases at the expense of Fe ions in the 3+ charge state. This effect is witnessed by photoluminescence (PL) measurements as changes in the intensity of the Fe 3+ -related intra-ionic transition, which can be controlled by co-doping with Si donors and Mg acceptors. In this regime, EPR of Fe 3+ ions and Curie-like magnetic susceptibility are observed. As a result of the spin-orbit interaction, Fe 2+ does not produce any EPR response. However, the presence of Fe ions in the 2+ charge state may account for a temperature-independent Van Vleck-type paramagnetic signal that we observe by SQUID magnetometry. Surprisingly, at higher Fe concentrations, the electron density is found to increase substantially with the Fe content. The co-existence of electrons in the conduction band and Fe in the 3+ charge state is linked to the gradient in the Fe concentration. In layers with iron content x 0.4% the presence of ferromagnetic signatures, such as magnetization hysteresis and spontaneous magnetization, have been detected. A set of precautions has been undertaken in order to rule out possible sources of spurious ferromagnetic contributions. Under these conditions, a ferromagnetic-like response is shown to arise from the (Ga,Fe)N epilayers, it increases with the iron concentration, it persists up to room temperature, and it is anisotropic -i.e., the saturation value of the magnetization is higher for in-plane magnetic field. We link the presence of ferromagnetic signatures to the formation of Fe-rich nanocrystals, as evidenced by TEM and EDS studies. This interpretation is supported by magnetization measurements after cooling in-and without an external magnetic field, pointing to superparamagnetic properties of the system. It is argued that the high temperature ferromagnetic response due to spinodal decomposition into regions with small and large concentration of the magnetic component is a generic property of diluted magnetic semiconductors and diluted magnetic oxides showing high apparent Curie temperature.

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Section: Introductionmentioning

confidence: 97%

ParamagneticGaN:Feand ferromagnetic(Ga,Fe)N: The relationship between structural, electronic, and magnetic properties

et al. 2007

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“…[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.…”

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confidence: 99%

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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“…2 The corresponding materials are classified as diluted magnetic semiconductors (DMS). Considerable success has been achieved in this direction in the domain of III-V and group IV semiconductors [3][4][5] , with some recent success reported in oxide-based systems [6][7][8][9][10][11] . Unfortunately in the case of many systems, researchers have not yet been able to completely rule out the possibilities of extrinsic effects such as dopant clustering, impurity magnetic phases etc.…”

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confidence: 99%

Electric Field Effect in Diluted Magnetic Insulator AnataseCo: TiO2

et al. 2005

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An external electric field induced reversible modulation of room temperature magnetic moment is achieved in an epitaxial and insulating thin film of dilutely cobalt-doped anatase TiO 2 . This first demonstration of electric field effect in any oxide based diluted ferromagnet is realized in a high quality epitaxial heterostructure of PbZr 0.2 Ti 0.8 O 3 /Co:TiO 2 /SrRuO 3 grown on (001) LaAlO 3 . The observed effect, which is about 15% in strength in a given heterostructure, can be modulated over several cycles.Possible mechanisms for electric field induced modulation of insulating ferromagnetism are discussed.

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Oxide-diluted magnetic semiconductors: a review of the experimental status

Cited by 415 publications

References 58 publications

ParamagneticGaN:Feand ferromagnetic(Ga,Fe)N: The relationship between structural, electronic, and magnetic properties

ParamagneticGaN:Feand ferromagnetic(Ga,Fe)N: The relationship between structural, electronic, and magnetic properties

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

Electric Field Effect in Diluted Magnetic Insulator AnataseCo: TiO2

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