Carrier-mediated interaction of magnetic moments in oxygen vacancy–controlled epitaxial Mn-doped ZnO thin films
TL;DR: In this article, an Epitaxial Zn0.98Mn 0.02O thin films were grown on c-cut sapphire substrates under various ambient oxygen pressures (pO2) using pulsed laser deposition.
Abstract: Epitaxial Zn0.98Mn0.02O thin films were grown on c-cut sapphire substrates under various ambient oxygen pressures (pO2) using pulsed laser deposition. The variation of pO2 during the growth process allowed for the control of intrinsic oxygen vacancies and resulting carrier densities in the films. While no impurity phase contributions were detected, a strong correlation between the effective carrier densities and the observed ferromagnetism (FM) was established. The magnetic data was consistent with a Ruderman-Kittel-Kasuya-Yosida (RKKY) exchange mechanism. The average spin-spin interaction energy for RKKY at 10 K was found to be smaller than the thermal energy, ensuring the availability of carriers to mediate RKKY-type FM, even at low temperatures.
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TL;DR: In this paper, a hexagonal wurtzite structure of pure ZnO was revealed by X-ray diffraction, which was attributed to the oxygen vacancies induced Cu2+ ferromagnetic coupling.
75 citations
TL;DR: In this article, a series of Zn1−xFexO films with different Fe concentrations (x = 0, 2.3, 5.4, 7.1, and 9.3 at) were prepared to investigate their structural, piezoelectric, ferroelectric, bipolar resistive switching properties.
Abstract: Valence state of Fe ions plays an important role in the physical properties of Fe doped ZnO films. Here, a series of Zn1−xFexO films with different Fe concentrations (x = 0, 2.3, 5.4, 7.1, and 9.3 at. %) were prepared to investigate their structural, piezoelectric, ferroelectric, bipolar resistive switching properties, and electrical-control of ferromagnetism at room temperature. The structure characterizations indicate that the chemical state of Fe ions substituting Zn2+ site changes from Fe3+ to Fe2+ with the increase of Fe dopant concentration. We found enhanced piezoelectric and ferroelectric properties in Zn0.977Fe0.023O films with more Fe3+ due to the smaller Fe3+ ionic size in comparison with Zn2+ while the increase of Fe2+ concentration by a larger amount of Fe dopant results in the worse ferroelectric and piezoelectric performance. All Pt/Zn1−xFexO/Pt devices show bipolar resistive switching properties. Especially, devices with lower Fe dopant concentration exhibit better endurance properties due to their higher crystalline quality. The variation of oxygen vacancies during resistive switching provides an opportunity to tune ferromagnetism of Fe-doped ZnO films, giving rise to the integration of charge and spin into a simple Pt/Zn1−xFexO/Pt devices. The multifunctional properties of Fe-doped ZnO films are promising for communication systems and information storage devices.
40 citations
TL;DR: The influence of growth oxygen pressure on the crystal structure and properties of anatase Fe0.05Ti0.95O2−δ semiconductor films has been investigated systematically.
19 citations
TL;DR: In this paper, the influence of various plasma species on the growth and structural properties of indium nitride in plasma-assisted metalorganic chemical vapor deposition was reported, and atomic emission spectroscopy was used to quantify the molecular, neutral, and ionized nitrogen species concentrations above the growth surface.
Abstract: We report on the influence of various plasma species on the growth and structural properties of indium nitride in plasma-assisted metalorganic chemical vapor deposition. Atomic emission spectroscopy was used to quantify the molecular, neutral, and ionized nitrogen species concentrations above the growth surface. Reflectance and Raman spectroscopy and X-ray diffraction techniques were used to characterize the grown InN films. It has been found that ionized rather than molecular or neutral nitrogen species is positively correlated with the InN growth rate. We conclude that InN formation in the present case is due to the chemical combination of atomic nitrogen ions with indium.
10 citations
TL;DR: In this paper, the authors investigated the influence of the concentration of oxygen vacancy on the dielectric relaxation of perovskite oxide thin films and found that low-temperature relaxor response is possibly caused by dipolar clusters that are formed by the aggregation of correlated dipolar defects within the films deposited under different ambient oxygen pressures.
Abstract: Dielectric relaxation in ferroelectric perovskites can result from different inherent chemical and charge disorders within their crystal structures. Despite several theories on dielectric relaxations, the relationship between the concentration of oxygen vacancy (${V}_{\mathrm{O}}$) and dielectric relaxation has not been studied in perovskite oxide thin films. In this work, we report a systematic investigation on the influence of the ${V}_{\mathrm{O}}^{\ensuremath{'}}\mathrm{s}$ on the dielectric relaxation of ${\mathrm{Ba}}_{0.85}{\mathrm{Ca}}_{0.15}{\mathrm{Ti}}_{0.9}{\mathrm{Zr}}_{0.1}{\mathrm{O}}_{3}$ (BCZT) epitaxial thin films grown with ${\mathrm{La}}_{0.7}{\mathrm{Sr}}_{0.3}{\mathrm{MnO}}_{3}$ (LSMO) top and bottom electrodes on single-crystal ${\mathrm{SrTiO}}_{3}$ (100) substrates using pulsed laser deposition. The ambient oxygen pressures during film growth were systematically varied to control the concentration of ${V}_{\mathrm{O}}$ in the epitaxial BCZT thin films. Low ambient oxygen pressure was found to enhance the tetragonality of the BCZT films and a systematic decrease in the tetragonality was observed at high oxygen pressure conditions as evidenced from x-ray diffraction (XRD) studies. Temperature dependent XRD analyses indicated a low-temperature anomaly near $\ensuremath{\sim}160\phantom{\rule{0.16em}{0ex}}\mathrm{K}$ in the BCZT/LSMO heterostructures. Low-temperature dielectric measurements revealed relaxor dielectric response with broad frequency dependence of the dielectric constant. It is proposed that the low-temperature dielectric relaxation is possibly caused by dipolar clusters that are formed by the aggregation of correlated ${V}_{\mathrm{O}}$-induced dipolar defects within the films deposited under different ambient oxygen pressures. High-resolution transmission electron microscopy suggested the presence of the nanometer-sized ${V}_{\mathrm{O}}$ clusters as represented by the structural defects of average diameters of $\ensuremath{\sim}5\phantom{\rule{0.16em}{0ex}}\mathrm{nm}$ in the BCZT films grown at variable ambient oxygen pressure. Activation energies of the aforesaid dipolar clusters, obtained from the Vogel-Fulcher fitting of the dielectric dispersion, showed a gradual increase in magnitude, as well as decreasing freezing temperatures, with decreasing concentrations of ${V}_{\mathrm{O}}$ in the BCZT films. From the theoretical analysis of the experimental data, it is postulated that the presence of the ${V}_{\mathrm{O}}$-induced dipolar defects affects the low-temperature dielectric relaxation in the BCZT thin films. This work significantly extends the understanding of ${V}_{\mathrm{O}}$-mediated dielectric relaxor behavior in complex perovskite oxide films.
4 citations
References
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TL;DR: Zener's model of ferromagnetism, originally proposed for transition metals in 1950, can explain T(C) of Ga(1-)(x)Mn(x)As and that of its II-VI counterpart Zn(1)-Mn (x)Te and is used to predict materials with T (C) exceeding room temperature, an important step toward semiconductor electronics that use both charge and spin.
Abstract: Ferromagnetism in manganese compound semiconductors not only opens prospects for tailoring magnetic and spin-related phenomena in semiconductors with a precision specific to III-V compounds but also addresses a question about the origin of the magnetic interactions that lead to a Curie temperature (T(C)) as high as 110 K for a manganese concentration of just 5%. Zener's model of ferromagnetism, originally proposed for transition metals in 1950, can explain T(C) of Ga(1-)(x)Mn(x)As and that of its II-VI counterpart Zn(1-)(x)Mn(x)Te and is used to predict materials with T(C) exceeding room temperature, an important step toward semiconductor electronics that use both charge and spin.
7,062 citations
TL;DR: It is proposed thatferromagnetic exchange here, and in dilute ferromagnetic nitrides, is mediated by shallow donor electrons that form bound magnetic polarons, which overlap to create a spin-split impurity band.
Abstract: Dilute ferromagnetic oxides having Curie temperatures far in excess of 300 K and exceptionally large ordered moments per transition-metal cation challenge our understanding of magnetism in solids. These materials are high-k dielectrics with degenerate or thermally activated n-type semiconductivity. Conventional super-exchange or double-exchange interactions cannot produce long-range magnetic order at concentrations of magnetic cations of a few percent. We propose that ferromagnetic exchange here, and in dilute ferromagnetic nitrides, is mediated by shallow donor electrons that form bound magnetic polarons, which overlap to create a spin-split impurity band. The Curie temperature in the mean-field approximation varies as (xdelta)(1/2) where x and delta are the concentrations of magnetic cations and donors, respectively. High Curie temperatures arise only when empty minority-spin or majority-spin d states lie at the Fermi level in the impurity band. The magnetic phase diagram includes regions of semiconducting and metallic ferromagnetism, cluster paramagnetism, spin glass and canted antiferromagnetism.
2,743 citations
TL;DR: The first observations of ferromagnetism above room temperature for dilute (<4 at%) Mn-doped ZnO semiconductors are reported, promising new spintronic devices as well as magneto-optic components.
Abstract: The search for ferromagnetism above room temperature in dilute magnetic semiconductors has been intense in recent years. We report the first observations of ferromagnetism above room temperature for dilute ( 700 °C) methods were used, samples were found to exhibit clustering and were not ferromagnetic at room temperature. This capability to fabricate ferromagnetic Mn-doped ZnO semiconductors promises new spintronic devices as well as magneto-optic components.
1,652 citations
TL;DR: In this paper, the magnetic properties of an oxide-diluted magnetic semiconductor (DMS), Zn0.64Mn 0.36O, were investigated and the temperature dependence of the magnetization showed a spin-glass behavior with the large magnitude of the Curie-Weiss temperature.
Abstract: We report on the magnetic properties of an oxide-diluted magnetic semiconductor (DMS), Zn0.64Mn0.36O. The temperature dependence of the magnetization shows a spin-glass behavior with the large magnitude of the Curie–Weiss temperature, corresponding to a stronger antiferromagnetic exchange coupling than other II–VI DMSs. The small effective Mn moment (x∼0.02) under high field also represents a strong antiferromagnetic exchange coupling in this compound.
654 citations
TL;DR: In this paper, the properties of Zn1−xMnxO (x=0.1 and 0.3) thin films grown on Al2O3(00⋅1) substrates using laser molecular-beam epitaxy were investigated.
Abstract: We report on ferromagnetic characteristics of Zn1−xMnxO (x=0.1 and 0.3) thin films grown on Al2O3(00⋅1) substrates using laser molecular-beam epitaxy. By increasing the Mn content, the films exhibited increases in both the c-axis lattice constant and fundamental band gap energy. The Curie temperature obtained from temperature-dependent magnetization curves was 45 K for the film with x=0.3, depending on the Mn composition in the films. The remanent magnetization and coercive field of Zn0.9Mn0.1O at 5 K were 0.9 emu/g and 300 Oe, respectively. For Zn0.7Mn0.3O, the remanent magnetization at 5 K increased to 3.4 emu/g.
518 citations