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We report on the structural and magnetic properties of a cobalt-implanted ZnO film grown on a sapphire substrate. X-ray diffraction and transmission electron microscopy reveal the presence of a ( )-oriented hexagonal Co phase in the Al2O3 sapphire substrate, but not in the ZnO film. Co clusters, with a diameter of about 5-6 nm, form a Co rich layer in the substrate close to the ZnO/Al2O3 interface. Magnetization measurements indicate that there exist two different magnetic phases in the implanted region. One originates from the Co clusters in Al2O 3, the other one belongs to a homogeneous ferromagnetic phase with a ferromagnetic Curie temperature far above room temperature. In the latter case, the ferromagnetism can be attributed to Co substitution on Zn sites in the ZnO layer. We have observed magnetic dichroism at the Co L2,3 and O K edges at room temperature as well as the multiplet structure in x-ray absorption spectra around the Co L3 edge, supporting the intrinsic nature of the observed ferromagnetism in a Co-implanted ZnO film. The magnetic moment per substituted cobalt is found to be about 2.81 νB, which is very close to the theoretical expected value of 3 νB/Co for Co 2+ in its high spin state. © 2008 IOP Publishing Ltd.

We report on the structural and magnetic properties of a cobalt-implanted ZnO film grown on a sapphire substrate. X-ray diffraction and transmission electron microscopy reveal the presence of a ( )-oriented hexagonal Co phase in the Al2O3 sapphire substrate, but not in the ZnO film. Co clusters, with a diameter of about 5-6 nm, form a Co rich layer in the substrate close to the ZnO/Al2O3 interface. Magnetization measurements indicate that there exist two different magnetic phases in the implanted region. One originates from the Co clusters in Al2O 3, the other one belongs to a homogeneous ferromagnetic phase with a ferromagnetic Curie temperature far above room temperature. In the latter case, the ferromagnetism can be attributed to Co substitution on Zn sites in the ZnO layer. We have observed magnetic dichroism at the Co L2,3 and O K edges at room temperature as well as the multiplet structure in x-ray absorption spectra around the Co L3 edge, supporting the intrinsic nature of the observed ferromagnetism in a Co-implanted ZnO film. The magnetic moment per substituted cobalt is found to be about 2.81 νB, which is very close to the theoretical expected value of 3 νB/Co for Co 2+ in its high spin state. © 2008 IOP Publishing Ltd.

The dose dependence of magnetism in Co-implanted TiO2 rutile was investigated using the magneto-optic Kerr effect method at room temperature. The (100)- and (001)-oriented single-crystalline rutile TiO2 plates were used as substrates and implanted by Co ions with a varying dose range of 0.25-1.50×1017 ions/cm2. We observed paramagnetic behaviour for the low dose doped samples, but obtain clear hysteretic-like behaviour for intermediate and high dose doped samples. For the intermediate implantation doses of Co, ferromagnetic behaviour can be explained by the F-center (oxygen vacancies) exchange mechanism, while for the highest implantation dose, in addition to Co substitution on Ti sites, formation of Co nanoclusters may take place within the TiO2 irradiated region. © 2006 Elsevier Ltd. All rights reserved.

We have studied the magnetic properties of the Co-implanted TiO2 thin films by magneto-optical Kerr effect (MOKE) and superconducting quantum interference device (SQUID) techniques. The single-crystalline (1 0 0), (0 0 1) and (1 1 0) TiO2 substrates of rutile structure have been heavily irradiated by Co+ ions with an energy of 40 keV to a dose of 1.5×1017 ion/cm2. Both techniques revealed strong room-temperature ferromagnetism, with magnetic parameters depending on the crystallographic orientation of the substrate. It has been observed by MOKE that the angular dependencies of the magnetic remanence and of the coercive field indicate a two-fold in-plane anisotropy for the (1 0 0) and (1 1 0) substrate and a four-fold in-plane anisotropy for the (0 0 1) substrate samples. SQUID measurements at room and low temperatures confirm the MOKE results. We also discuss the origin of the ferromagnetism emerging in dielectric and diamagnetic single-crystalline TiO2 substrates after Co-ion implantation. © 2005 Elsevier B.V. All rights reserved.

We report on structural, magnetic and electronic properties of Co-implanted TiO2(1 0 0) rutile single crystals for different implantation doses. Strong ferromagnetism at room temperature and above is observed in TiO 2 rutile plates after cobalt ion implantation, with magnetic parameters depending on the cobalt implantation dose. While the structural data indicate the presence of metallic cobalt clusters, the multiplet structure of the Co L3 edge in the XAS spectra provides evidence that a sizeable portion of the dopants occupy substitutional Co2+ sites. The detailed analysis of the structural and magnetic properties indicates that there are two magnetic phases in Co-implanted TiO2 plates. One is a ferromagnetic phase due to the formation of long range ferromagnetic ordering between implanted magnetic cobalt ions in the rutile phase, and the second one is a superparamagnetic phase which originates from the formation of metallic cobalt clusters in the implanted region. Using x-ray resonant magnetic scattering, the element specific magnetizations of cobalt, oxygen and titanium in Co-implanted TiO2 single crystals are investigated. Magnetic dichroism was observed at the Co L2,3 edges as well as at the O K edge. Anomalous Hall effect measurement indicates n-type carriers in Co-implanted TiO 2 rutile. The interaction mechanism, which leads to ferromagnetic ordering of substituted cobalt ions in the host matrix, is also discussed. © 2009 IOP Publishing Ltd.

We have studied the structural, magnetic, and electronic properties of Co-implanted ZnO(0001) films grown on Al2 O3 (11 2- 0) substrates for different implantation doses and over a wide temperature range. Strong room temperature ferromagnetism is observed with magnetic parameters depending on the cobalt implantation dose. A detailed analysis of the structural and magnetic properties indicates that there are two magnetic phases in Co-implanted ZnO films. One is a ferromagnetic phase due to the formation of long range ferromagnetic ordering between implanted magnetic cobalt ions in the ZnO layer and the second one is a superparamagnetic phase, which occurs due to the formation of metallic cobalt clusters in the Al2 O3 substrate. Using x-ray resonant magnetic scattering, the element specific magnetization of cobalt, oxygen, and Zn was investigated. Magnetic dichroism was observed at the Co L2,3 edges as well as at the O K edge. In addition, the anomalous Hall effect is also observed, supporting the intrinsic nature of ferromagnetism in Co-implanted ZnO films. © 2009 American Institute of Physics.

Of central interest in the research of dilute magnetic semiconductors is the coupling mechanism leading to a ferromagnetic ground state. Using x-ray resonant magnetic scattering, we have analyzed the element specific magnetic hysteresis curves of Co, Ti, and oxygen in Co-doped Ti O2 synthesized by ion implantation. Magnetic dichroism was observed at the Co L2,3 edges, as well as at the O K edge, indicative of a spin polarization of oxygen atoms in the Ti O2 host matrix. The hysteretic shapes and the coercive field values measured at the Co L3 and O K edges are identical (1.9 kOe at 30 K). © 2006 American Institute of Physics.

Magnetic anisotropy of cobalt implanted single-crystalline rutile has been studied by means of magneto-optical Kerr effect (MOKE) and superconducting quantum interference device (SQUID) techniques. We observed for the first time strong angular dependence of the remanent magnetization and coercive field in the plane of the implanted surface: twofold anisotropy for the (100)-substrate and fourfold anisotropy for the (001)-substrate samples. The observation opens up new possibilities to tailor magnetic anisotropies of the material. Possible origins of ferromagnetism and anisotropies in dielectric and diamagnetic single-crystalline TiO2 samples after Co-ion implantation are discussed. © 2005 IOP Publishing Ltd.

Of central interest in the research of dilute magnetic semiconductors is the coupling mechanism leading to a ferromagnetic ground state. Using x-ray resonant magnetic scattering, we have analyzed the element specific magnetic hysteresis curves of Co, Ti, and oxygen in Co-doped Ti O2 synthesized by ion implantation. Magnetic dichroism was observed at the Co L2,3 edges, as well as at the O K edge, indicative of a spin polarization of oxygen atoms in the Ti O2 host matrix. The hysteretic shapes and the coercive field values measured at the Co L3 and O K edges are identical (1.9 kOe at 30 K). © 2006 American Institute of Physics.

Magnetic anisotropy of cobalt implanted single-crystalline rutile has been studied by means of magneto-optical Kerr effect (MOKE) and superconducting quantum interference device (SQUID) techniques. We observed for the first time strong angular dependence of the remanent magnetization and coercive field in the plane of the implanted surface: twofold anisotropy for the (100)-substrate and fourfold anisotropy for the (001)-substrate samples. The observation opens up new possibilities to tailor magnetic anisotropies of the material. Possible origins of ferromagnetism and anisotropies in dielectric and diamagnetic single-crystalline TiO2 samples after Co-ion implantation are discussed. © 2005 IOP Publishing Ltd.

The dose dependence of magnetism in Co-implanted TiO2 rutile was investigated using the magneto-optic Kerr effect method at room temperature. The (100)- and (001)-oriented single-crystalline rutile TiO2 plates were used as substrates and implanted by Co ions with a varying dose range of 0.25-1.50×1017 ions/cm2. We observed paramagnetic behaviour for the low dose doped samples, but obtain clear hysteretic-like behaviour for intermediate and high dose doped samples. For the intermediate implantation doses of Co, ferromagnetic behaviour can be explained by the F-center (oxygen vacancies) exchange mechanism, while for the highest implantation dose, in addition to Co substitution on Ti sites, formation of Co nanoclusters may take place within the TiO2 irradiated region. © 2006 Elsevier Ltd. All rights reserved.

We have studied the magnetic properties of the Co-implanted TiO2 thin films by magneto-optical Kerr effect (MOKE) and superconducting quantum interference device (SQUID) techniques. The single-crystalline (1 0 0), (0 0 1) and (1 1 0) TiO2 substrates of rutile structure have been heavily irradiated by Co+ ions with an energy of 40 keV to a dose of 1.5×1017 ion/cm2. Both techniques revealed strong room-temperature ferromagnetism, with magnetic parameters depending on the crystallographic orientation of the substrate. It has been observed by MOKE that the angular dependencies of the magnetic remanence and of the coercive field indicate a two-fold in-plane anisotropy for the (1 0 0) and (1 1 0) substrate and a four-fold in-plane anisotropy for the (0 0 1) substrate samples. SQUID measurements at room and low temperatures confirm the MOKE results. We also discuss the origin of the ferromagnetism emerging in dielectric and diamagnetic single-crystalline TiO2 substrates after Co-ion implantation. © 2005 Elsevier B.V. All rights reserved.

We report on structural, magnetic and electronic properties of Co-implanted TiO2(1 0 0) rutile single crystals for different implantation doses. Strong ferromagnetism at room temperature and above is observed in TiO 2 rutile plates after cobalt ion implantation, with magnetic parameters depending on the cobalt implantation dose. While the structural data indicate the presence of metallic cobalt clusters, the multiplet structure of the Co L3 edge in the XAS spectra provides evidence that a sizeable portion of the dopants occupy substitutional Co2+ sites. The detailed analysis of the structural and magnetic properties indicates that there are two magnetic phases in Co-implanted TiO2 plates. One is a ferromagnetic phase due to the formation of long range ferromagnetic ordering between implanted magnetic cobalt ions in the rutile phase, and the second one is a superparamagnetic phase which originates from the formation of metallic cobalt clusters in the implanted region. Using x-ray resonant magnetic scattering, the element specific magnetizations of cobalt, oxygen and titanium in Co-implanted TiO2 single crystals are investigated. Magnetic dichroism was observed at the Co L2,3 edges as well as at the O K edge. Anomalous Hall effect measurement indicates n-type carriers in Co-implanted TiO 2 rutile. The interaction mechanism, which leads to ferromagnetic ordering of substituted cobalt ions in the host matrix, is also discussed. © 2009 IOP Publishing Ltd.

We have studied the structural, magnetic, and electronic properties of Co-implanted ZnO(0001) films grown on Al2 O3 (11 2- 0) substrates for different implantation doses and over a wide temperature range. Strong room temperature ferromagnetism is observed with magnetic parameters depending on the cobalt implantation dose. A detailed analysis of the structural and magnetic properties indicates that there are two magnetic phases in Co-implanted ZnO films. One is a ferromagnetic phase due to the formation of long range ferromagnetic ordering between implanted magnetic cobalt ions in the ZnO layer and the second one is a superparamagnetic phase, which occurs due to the formation of metallic cobalt clusters in the Al2 O3 substrate. Using x-ray resonant magnetic scattering, the element specific magnetization of cobalt, oxygen, and Zn was investigated. Magnetic dichroism was observed at the Co L2,3 edges as well as at the O K edge. In addition, the anomalous Hall effect is also observed, supporting the intrinsic nature of ferromagnetism in Co-implanted ZnO films. © 2009 American Institute of Physics.