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Journal ArticleDOI

Room temperature ferromagnetism in HfO2 films

01 Apr 2011-Journal of Applied Physics (American Institute of Physics)-Vol. 109, Iss: 7

Abstract: HfO2 films were produced by sputter deposition in the substrate temperature (Ts) range of room temperature (RT)−300 °C and their structural, magnetic, and electrical properties were evaluated. The results indicate that the HfO2 films crystallize in the monoclinic structure and are oriented along the (−111) direction. Magnetization measurements (300–1.8 K) evidence their RT ferromagnetism. The effect of Ts is significant on the magnetic moment (M) and coercivity (Hc). M and Hc values enhanced with increasing Ts due to formation of oxygen vacancies. Increase in the temperature from 150 to 300 K decreases Hc without any transition, indicating that the Curie temperature of HfO2 films is higher than RT. Electrical measurements indicate that the HfO2 films are semiconducting.
Topics: Magnetic semiconductor (56%), Curie temperature (56%), Ferromagnetism (54%), Magnetization (53%), Coercivity (53%)
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Journal ArticleDOI
Abstract: Y-doped HfO2 nanopowders, produced by metathesis synthesis, exhibit ferromagnetism at room temperature. The X-ray diffraction and Raman measurements have shown that HfO2 nanopowders undergo phase transformation from monoclinic to tetragonal and cubic phase with increasing of Y content. The X-ray photoelectron spectroscopy and Raman analysis gave evidence that Y-doped HfO2 nanopowders are oxygen deficient. The ferromagnetic properties of Y-doped HfO2 nanocrystals are dependent on crystal structure changes. The structural transformation from monoclinic to tetragonal phase with Y doping is followed by increased ferromagnetic ordering because of the increased concentration of oxygen vacancies (VO) in different charge states. Higher Y content favors the formation of cubic phase and the ferromagnetism significantly weakens. In cubic hafnia phase, yttrium can form (VO–YHf) defect complexes in different charge states. The appearance of these complexes can be responsible for the degradation of ferromagnetic ordering.

15 citations

Cites background or result from "Room temperature ferromagnetism in ..."

  • ...Having in mind theoretical calculations [7,36] and experimental observations [30–33] and knowing from the Raman and XPS results that Hf1 xYxO2 δ nanopowders are oxygen deficient, we concluded that the oxygen vacancies can be attributed to be the main source of ferromagnetism in undoped and Y-doped HfO2 nanopowders....


  • ...The experimental reports [30–33] confirmed the existence of RTFM in pure and doped hafnia films and clearly proved that the RTFM originates from the presence of oxygen vacancies....


Journal ArticleDOI
Abstract: Whether or not nanoscale HfO2 has ferromagnetism is a debatable issue. In this study, monoclinic HfO2 nanorods with an average size of about 33.7 ± 3.1 nm in length and 8.9 ± 0.7 nm in width were synthesized via a chemical solution method. In comparison with many HfO2 nanoparticles/nanoclusters synthesized by physical methods, the as-prepared HfO2 nanorods were characterized by their better crystallinity and anisotropic shape. Interestingly, although the pristine HfO2 nanorods showed overall paramagnetic characteristics, when the nanorods were annealed in reducing environment, they exhibited clear room-temperature ferromagnetism (RTFM). The observed RTFM probably resulted from oxygen vacancies generated in the annealing process. In the mean time, it is suggested that factors such as the dimension, specific shape, and crystallinity of the HfO2 materials also should not be ignored when correlating the occurrence of ferromagnetism with defects.

7 citations

20 Jan 2017
Abstract: In the recent years, silicon has emerged as a promising host material for spin qubits. Thanks to its widespread use in modern microelectronics, silicon technology has seen a tremendous development. Realizing qubit devices using well-established complementary metal-oxide-semiconductor (CMOS) fabrication technology would clearly favor their large scale integration.In this thesis we present a detailed study on CMOS devices in a perspective of qubit operability.In particular we tackled the problems of charge and spin confinement in quantum dots, spin manipulation and charge and spin readout.We explored the different charge and spin confinement capabilities of samples with different sizes and geometries. Ultrascaled MOSFETs show Coulomb blockade up to room temperature with charging energies up to 200meV. Multigate devices with larger geometrical dimensions have been used to confine spins and read their states through spin-blockade as a way to perform spin to charge conversion.Spin manipulation is achieved by means of Electron Dipole induced Spin Resonance (EDSR). The two lowest valleys of silicon's conduction band originate as intra and inter-valley spin transitions; we probe a valley splitting of 36μeV. The origin of this spin resonance is explained as an effect of the specific geometry of the sample combined with valley physics and Rashba spin-orbit interaction. Signatures of coherent Rabi oscillations have been measured, with a Rabi frequency of 6MHz. We also discuss fast charge and spin readout performed by dispersive gate-coupled reflectometry. We show how to use it to recover the complete charge stability diagram of the device and the expected signal for an isolated double dot system. Finite bias changes the response of the system and we used it to probe excited states and their dynamics.

7 citations

Journal ArticleDOI
Xing Wang1, Congmian Zhen1, Xiao-Wei Liu1, Liu Xiumin1  +3 moreInstitutions (1)
Abstract: A simple and effective method to prepare a weakly ferromagnetic SiO 2 nanoarray with a hole-bridge structure is described. The SiO 2 nanospheres were prepared using a modified Stober method. The array was obtained through three-dimensional self-organization from a SiO 2 aqueous suspension by vertical deposition. Sintering makes the array more regular than the as-deposited state, and additional oxygen vacancies were produced during sintering. We obtained the hole-bridge structure by etching the sintered array using HF. Compared with other structures, the hole-bridge structure gives the largest magnetic signal at room temperature (0.016 ∼ emu/cm 3 ). Oxygen vacancies in the SiO 2 nanospheres are thought to be responsible in large measure for the ferromagnetism, and defects from the HF-etching make the SiO 2 nanoarray with a hole-bridge structure show stronger ferromagnetic behavior.

6 citations

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01 Jan 2001

19,319 citations

01 Jan 1956
Abstract: 1. Properties of X-rays. 2. Geometry of Crystals. 3. Diffraction I: Directions of Diffracted Beams. 4. Diffraction II: Intensities of Diffracted Beams. 5. Diffraction III: Non-Ideal Samples. 6. Laure Photographs. 7. Powder Photographs. 8. Diffractometer and Spectrometer. 9. Orientation and Quality of Single Crystals. 10. Structure of Polycrystalline Aggregates. 11. Determination of Crystal Structure. 12. Precise Parameter Measurements. 13. Phase-Diagram Determination. 14. Order-Disorder Transformation. 15. Chemical Analysis of X-ray Diffraction. 16. Chemical Analysis by X-ray Spectrometry. 17. Measurements of Residual Stress. 18. Polymers. 19. Small Angle Scatters. 20. Transmission Electron Microscope.

17,396 citations

Journal ArticleDOI
Abstract: Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems. This article reviews the current status of this subject, including both recent advances and well-established results. The primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport in semiconductors and metals. Spin transport differs from charge transport in that spin is a nonconserved quantity in solids due to spin-orbit and hyperfine coupling. The authors discuss in detail spin decoherence mechanisms in metals and semiconductors. Various theories of spin injection and spin-polarized transport are applied to hybrid structures relevant to spin-based devices and fundamental studies of materials properties. Experimental work is reviewed with the emphasis on projected applications, in which external electric and magnetic fields and illumination by light will be used to control spin and charge dynamics to create new functionalities not feasible or ineffective with conventional electronics.

8,325 citations

Journal ArticleDOI
Abstract: Many materials systems are currently under consideration as potential replacements for SiO2 as the gate dielectric material for sub-0.1 μm complementary metal–oxide–semiconductor (CMOS) technology. A systematic consideration of the required properties of gate dielectrics indicates that the key guidelines for selecting an alternative gate dielectric are (a) permittivity, band gap, and band alignment to silicon, (b) thermodynamic stability, (c) film morphology, (d) interface quality, (e) compatibility with the current or expected materials to be used in processing for CMOS devices, (f) process compatibility, and (g) reliability. Many dielectrics appear favorable in some of these areas, but very few materials are promising with respect to all of these guidelines. A review of current work and literature in the area of alternate gate dielectrics is given. Based on reported results and fundamental considerations, the pseudobinary materials systems offer large flexibility and show the most promise toward success...

5,532 citations

Journal ArticleDOI
31 Aug 2000-Nature
TL;DR: Development of higher permittivity dielectrics for dynamic random-access memories serves to illustrate the magnitude of the now urgent problem of identifying alternatives to silicon dioxide for the gate dielectric in logic devices, such as the ubiquitous field-effect transistor.
Abstract: The silicon-based microelectronics industry is rapidly approaching a point where device fabrication can no longer be simply scaled to progressively smaller sizes. Technological decisions must now be made that will substantially alter the directions along which silicon devices continue to develop. One such challenge is the need for higher permittivity dielectrics to replace silicon dioxide, the properties of which have hitherto been instrumental to the industry's success. Considerable efforts have already been made to develop replacement dielectrics for dynamic random-access memories. These developments serve to illustrate the magnitude of the now urgent problem of identifying alternatives to silicon dioxide for the gate dielectric in logic devices, such as the ubiquitous field-effect transistor.

1,128 citations

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