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Journal ArticleDOI

Room temperature ferromagnetism in HfO2 films

TL;DR: In this article, 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.
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.
Citations
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Dissertation
20 Jan 2017
TL;DR: In this article, a detailed study on metal-oxide-semiconductor (CMOS) devices in a perspective of qubit operability is presented, in particular the problems of charge and spin confinement in quantum dots, spin manipulation and charge and readout.
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
TL;DR: In this article, a combination of magnetic Pd NPs with UiO-66(Hf), which exhibits ferromagnetism, and corresponding modifications in the hybridized structures are found to be strongly ferromagnetic, showing high magnetization and coercivity.
Abstract: Nonmagnetic Pd exhibits ferromagnetism in the nanosize regime. Various stabilization agents, including surfactants, metal oxide supports, polymers, and porous materials (e.g., metal-organic frameworks (MOFs)), have been employed to prevent the agglomeration of metal nanoparticles. However, magnetic properties are greatly affected by the structural and electronic changes imposed by these stabilizing agents. In particular, metal-MOF hybrids (NPs@MOFs) have reduced magnetic properties, as reported by several authors. Herein, we report the enhancement in magnetic properties resulting from the combination of magnetic Pd NPs with UiO-66(Hf), which exhibits ferromagnetism, and the corresponding modifications in the hybridized structures. These hybridized structures are found to be strongly ferromagnetic, showing high magnetization and coercivity. We observed that the magnetic property is enhanced by 2 to 3 times upon including the Pd NPs on the surface of a UiO-66(Hf) shell support. For a fundamental understanding, the magnetization (M-H data) of the hybridized structure is analyzed with a modified Langevin function.

6 citations

Journal ArticleDOI
TL;DR: In this article, first-principles numerical simulations based on density functional theory are performed to examine surface electronic and magnetic properties of cubic, tetragonal, and monoclinic HfO 2 with low index terminations.

6 citations

Journal ArticleDOI
Li-qian Qi1, Di-Ya Pan1, Jun-Qing Li1, Lihu Liu1, Huiyuan Sun1 
TL;DR: HfO2 nanoporous films have been fabricated on porous anodic alumina substrates by DC-reactive magnetron sputtering by combining electric field control of magnetization change and RS, which makes HP films possible for the multifunctional data storage media materials.
Abstract: New materials for achieving direct electric field control of ferromagnetism and resistance behavior are highly desirable in the development of multifunctional data storage devices. In this paper, HfO2 nanoporous films have been fabricated on porous anodic alumina (PAA) substrates by DC-reactive magnetron sputtering. Electrically induced resistive switching (RS) and modulated room temperature ferromagnetism are simultaneously found in a Ag/HfO2/PAA/Al (Ag/HP/Al) heterostructure. The switching mechanism between low resistance state and high resistance state is generally attributed to the formation/rupture of conductive filaments which may consist of oxygen vacancies. The combination of the electric field control of magnetization change and RS makes HP films possible for the multifunctional data storage media materials.

4 citations

Journal ArticleDOI
TL;DR: In this paper, the magnetic properties of thin films of zirconia doped with Fe impurities were investigated using first-principles simulations and X-ray absorption near edge spectroscopy (XANES) in high magnetic fields.
Abstract: Exploiting first-principles simulations and x-ray absorption near edge spectroscopy (XANES) in high magnetic fields, we investigated the magnetic properties of thin films of zirconia doped with Fe impurities. In our ${\mathrm{Zr}}_{1\ensuremath{-}x}{\mathrm{Fe}}_{x}{\mathrm{O}}_{2\ensuremath{-}y}$ samples, grown by atomic layer deposition (ALD), the Fe dopants are uniformly distributed, ranging from diluted ($x\ensuremath{\simeq}2\text{--}3%$) up to high ($x\ensuremath{\simeq}25%$) atomic concentration. By x-ray magnetic circular dichroism (XMCD), we carefully analyzed, for samples having different Fe concentration, the magnetic moments as a function of temperature, in the range from 5 K up to 150 K, studying the best dopant concentration range maximizing the magnetic signal. Surprisingly, the iron magnetic moment measured for diluted concentrations degrades as the concentration of magnetic dopant increases. On the basis of ab initio simulations, we propose that the microscopic mechanisms responsible for the peculiar magnetic properties of this compound can be explained by oxygen-mediated superexchange mechanism between the Fe dopants producing, at high dopant concentration, an antiferromagnetic coupling between two Fe atoms. We identify and discuss the role of O vacancies to control such microscopic mechanisms.

1 citations

References
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Book
01 Jan 2001

19,319 citations

Book
01 Jan 1956
TL;DR: In this article, the authors present a chemical analysis of X-ray diffraction by Xray Spectrometry and phase-diagram Determination of single crystal structures and phase diagrams.
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.

17,428 citations

Journal ArticleDOI
TL;DR: Spintronics, or spin electronics, involves the study of active control and manipulation of spin degrees of freedom in solid-state systems as discussed by the authors, where the primary focus is on the basic physical principles underlying the generation of carrier spin polarization, spin dynamics, and spin-polarized transport.
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.

9,158 citations

Journal ArticleDOI
TL;DR: In this paper, a review of the 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.
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...

5,711 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.

1,179 citations