Structural dependent room-temperature ferromagnetism in yttrium doped HfO2 nanoparticles
TL;DR: Y-doped HfO2 nanopowders, produced by metathesis synthesis, exhibit ferromagnetism at room temperature as mentioned in this paper, and X-ray diffraction and Raman measurements have shown that Y doping is followed by increased ferromagnetic ordering because of the increased concentration of oxygen vacancies in different charge states.
About: This article is published in Ceramics International.The article was published on 2015-06-01. It has received 19 citations till now. The article focuses on the topics: Ferromagnetic material properties & Tetragonal crystal system.
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TL;DR: Two groups of materials strongly candidates to fabricate spintronics devices are highlighted, denoted diluted magnetic semiconductor and multiferroic materials.
Abstract: Spintronics is a promising technology which aims to solve the major problems existing in today’s conventional electronic devices. Realistically, this technology has the ability to combine the main functions of the modern semiconductor microelectronics and magnetic storage devices in single chip. Electrons have two fundamental degrees of freedom (DOF) called charge and spin. Conventional electronic devices used only the charge of electron for information processing using binary bits 0 and 1. The continuous developments in the conventional electronics are basically depending on reducing component size (transistors, capacitors, etc.) embedded in integrated circuits (random access memory, microprocessor, etc.). In 2019, the actual size of the transistor placed in commercial microprocessor is about 50 nm with gate length of 20 nm and node of 7 nm fabricated using TSMC’s 7-nm FinFET (Taiwan Semiconductor Manufacturing Company 7-nm Fin Field Effect Transistor). The progress in the electronic devices will come to the end when the transistor node size reaches to 1 nm. Below this size, the fabrication, writing, and reading processes will be difficult or impossible due to quantum size effect. Spintronics is the alternative future technology, which is based on using the fundamental spin of electron in additions to its charge to carry and store information. Transfer from conventional electronics to spintronics technology opens the possibilities to construct devices with high storage density, low power consummation, and fast operation and that are cheap and robust. The main aim of this work is to give a simple and clear picture to researchers who are beginners of research in this field. In this review, basic outlines of spintronics technology and its fundamental properties were discussed. Here, we highlight two groups of materials strongly candidates to fabricate spintronics devices, denoted diluted magnetic semiconductor and multiferroic materials.
57 citations
TL;DR: In this paper, the chemical bonding and composition of praseodymium doping-doped HfO2 thin film were characterized by X-ray photoelectron spectroscopy (XPS), while the structural properties were investigated by glancing incidence Xray diffraction (GIXRD) and high resolution transmission electron microscopy (HRTEM).
Abstract: HfO2 thin films with different praseodymium doping contents (Pr:HfO2) were fabricated by chemical solution deposition (CSD) method at ambient conditions. The chemical bonding and the composition of Pr doped HfO2 thin film were characterized by X-ray photoelectron spectroscopy (XPS), while the structural properties were investigated by glancing incidence X-ray diffraction (GIXRD) and high resolution transmission electron microscopy (HRTEM). It is found that the ferroelectric orthorhombic phase was induced in the HfO2 based thin films by Pr doping. The combined results of P–E (polarization–electrical field) and C–V (capacitance–voltage) measurements demonstrated that the 5 mol% Pr doped HfO2 film exhibited a distinct ferroelectricity, with a maximum remanent polarization (Pr) of 6.9 µC/cm2 and a coercive field (Ec) of 1.2 MV/cm. Notably, the polarization did not show obvious degradation over 1 × 108 switching cycles, suggesting good endurance performance of the Pr doped HfO2 thin film. These results indicate that Pr dopant could effectively induce ferroelectricity in HfO2 thin films, thereby becoming a new member of dopants for HfO2 based ferroelectrics.
24 citations
TL;DR: For the first time, the high temperature cubic phase of HfO2 at room temperature is stabilized by incorporating Dy, and a tentative energy band diagram is proposed illustrating the energetic processes taking place in Hf1-xDyxO2.
Abstract: Hafnium oxide (HfO2) can exist in different crystalline structures such as monoclinic at room temperature, tetragonal at 1700 °C and cubic at 2600 °C. In the present study, nanocrystalline powders of HfO2 synthesized by a Pechini type sol–gel technique show a monoclinic phase, P21/c, at room temperature. By incorporating Dy into the HfO2 lattice, the intensity of all diffraction peaks corresponding to P21/c decreases and at a concentration of 11 at% of Dy, the monoclinic phase transforms completely to the cubic phase, Fmm, showing a mixed phase of monoclinic and cubic at intermediate concentrations (5–9 at%) of Dy. For the first time, we have stabilized the high temperature cubic phase of HfO2 at room temperature by incorporating Dy. Selected area electron diffraction patterns confirm the monoclinic and the cubic phase as observed from the X-ray diffraction patterns. A mechanism for stabilization of the high temperature cubic phase in Hf1−xDyxO2 has been analyzed based on the substitution of dysprosium for hafnium ions and the formation of oxygen vacancies. While ferromagnetic ordering at room temperature observed in HfO2 nanoparticles is quenched after incorporating 1 at% of Dy, photoluminescence (PL) studies demonstrate excellent emissions in the blue and yellow region after exciting with UV light of wavelength 352 nm. Combining excitation and emission profiles, we have proposed a tentative energy band diagram illustrating the energetic processes taking place in Hf1−xDyxO2.
19 citations
TL;DR: In this paper, the effects of yttrium (Y) on the physicochemical characteristics of tin(II) dioxide (SnO2) nanoparticles (NPs), which were efficiently synthesized via a simple hydrothermal chemical route with different doping concentrations (0, 2 and 4 at%) of Y, were investigated.
Abstract: This review reports the effects of yttrium (Y) on the physicochemical characteristics of tin(II) dioxide (SnO2) nanoparticles (NPs), which were efficiently synthesized via a simple hydrothermal chemical route with different doping concentrations (0, 2 and 4 at%) of Y. The structural, optical and photocatalytic properties of the as-prepared Y-doped SnO2 (Y:SnO2) NPs were investigated, and the results are described. X-ray diffraction (XRD) studies showed that the undoped and Y:SnO2 NPs had a fine crystalline texture with a tetragonal structure and particle size range of 27–15 nm, although the size decreased with Y doping. High-resolution scanning electron microscopy (HRSEM) morphological analysis revealed spherical NPs forming agglomerates. Optical absorption was investigated by UV-visible diffuse reflectance spectroscopy, and showed a redshift in bandgap energy for Y3+-doped SnO2 NPs, and photoluminescence spectroscopy revealed the most intense emission peaks in the visible light region. Enhanced photocatalytic activity was observed for the doped samples, and the 4% Y:SnO2 NPs exhibited excellent photodegradation of methylene blue aqueous (MB) dye in visible light, demonstrating 92.34% degradation in 180 min. The other photocatalysts also demonstrated greater than 85% photodegradation efficiency and high stability, with no significant reduction in activity observed after five cycles. The results indicate that the superoxide (·O2−) radical, a key reactive species, played a vital role in the degradation of aqueous MB dye. The probable photocatalytic mechanism of the Y:SnO2 NPs was thoroughly investigated.
18 citations
References
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TL;DR: It is shown that thin films of hafnium dioxide (HfO2), an insulating oxide better known as a dielectric layer for nanoscale electronic devices, can be ferromagnetic even without doping.
Abstract: It is generally accepted that magnetic order in an insulator requires the cation to have partially filled shells of d or f electrons. Here we show that thin films of hafnium dioxide (HfO2), an insulating oxide better known as a dielectric layer for nanoscale electronic devices, can be ferromagnetic even without doping. This discovery challenges our understanding of magnetism in insulators, because neither Hf4+ nor O2- are magnetic ions and the d and f shells of the Hf4+ ion are either empty or full.
1,046 citations
"Structural dependent room-temperatu..." refers background in this paper
...The 5d electrons will in turn polarize the defect band establishing the ferromagnetic coupling [4]....
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...The discovery of unexpected roomtemperature ferromagnetism (RTFM) in undoped monoclinic HfO2 thin films [4] has opened a path to a new class of ferromagnetic materials which can play important role in new generation of spintronic devices....
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...[4]....
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...The formation of the spin-split defect band provides necessary condition for the appearance of ferromagnetism [4]....
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TL;DR: In this paper, a nonlinear calibration curve for volume fraction vs integrated intensity ratio was obtained for the monoclinic-tetragonal ZrO2 system by using X-ray powder pattern-fitting and pattern-decomposition techniques.
Abstract: A nonlinear calibration curve for volume fraction vs integrated intensity ratio was obtained for the monoclinic-tetragonal ZrO2 system by using X-ray powder pattern-fitting and pattern-decomposition techniques. The empirical equation agrees well with the theoretical one. By using this equation, the deviation from linearity (6.8% maximum) resulting from the intensity difference of corresponding reflections of the two phases can be estimated quite accurately.
835 citations
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TL;DR: In this article, the magnetic moment was observed in undoped semiconducting or insulating oxides to become ferromagnetic at room temperature on MgO substrates, where the magnetic field was applied parallel to the film plane.
Abstract: Remarkable room-temperature ferromagnetism was observed in undoped $\mathrm{Ti}{\mathrm{O}}_{2}$, $\mathrm{Hf}{\mathrm{O}}_{2}$, and ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ thin films. The magnetic moment is rather modest in the case of ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ films on MgO substrates (while on ${\mathrm{Al}}_{2}{\mathrm{O}}_{3}$ substrates, it is negative showing diamagnetism) when the magnetic field was applied parallel to the film plane. In contrast, it is very large in the other two cases (about 20 and $30\phantom{\rule{0.3em}{0ex}}\mathrm{emu}∕{\mathrm{cm}}^{3}$ for $200\text{\ensuremath{-}}\mathrm{nm}$-thick $\mathrm{Ti}{\mathrm{O}}_{2}$ and $\mathrm{Hf}{\mathrm{O}}_{2}$ films, respectively). Since bulk $\mathrm{Ti}{\mathrm{O}}_{2}$, $\mathrm{Hf}{\mathrm{O}}_{2}$, and ${\mathrm{In}}_{2}{\mathrm{O}}_{3}$ are clearly diamagnetic, and moreover, there are no contaminations in any substrate, we must assume that the thin film form, which might create necessary defects or oxygen vacancies, would be the reason for undoped semiconducting or insulating oxides to become ferromagnetic at room temperature.
772 citations
"Structural dependent room-temperatu..." refers background or result in this paper
...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....
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...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....
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