Optical properties and mechanical characteristics of transparent nanostructured Zn1−xMnxO thin films

Uniform and transparent thin films of Zn_1−xMn_xO (0?x?0.10) were fabricated by a sol-gel spin coating method. XRD results indicated the hexagonal structure of ZnO as the primary phase at all concentrations (x) of Mn. However, at x?0.035, Mn₃O₄ (tetragonal) is observed as the secondary phase, which was confirmed by selected-area electron diffraction patterns. SEM and TEM results showed a tendency of grains to arrange into wire-shaped morphologies, leading to elongated needle-like structures at high Mn addition. Increasing Mn content in the range 0?x?0.10 led to quenching of photoluminescence, increase in the band gap (E_g) from 3.27 to 3.33 eV, and increase in film thickness, refractive index and extinction coefficient of Zn_1−xMn_xO thin films. The residual stress evaluated was compressive in all cases and found to increase by an order of magnitude with addition of Mn. Furthermore, an overall increase in microhardness and yield strength of Zn_1−xMn_xO thin films at higher Mn concentrations is attributed to change in microstructures, presence of secondary phase and increase in film thickness.     

Structural and photoluminescence analysis of Zn1 − xMnxO nanocrystalline powders

This Letter reports on structural and photoluminescence properties of Zn_1 − xMn_xO nanocrystalline powders, which were synthesized by using oxalate precursor decomposition method. From the XRD features, we have noticed that all samples exhibit wurtzite crystal structure. The origin of photoluminescence properties of Mn doped and undoped ZnO have been discussed.     

Influence of Hf doping concentration on microstructure and optical properties of HfxZn1−xO thin films

Hf_xZn_1−xO thin films (x=3, 7, 10 and 15 mol%) were deposited on Si (1 0 0) using pulsed laser deposition. The influence of the Hf concentration on the microstructure and optical properties of the films was studied. It is found that Hf ions can be effectively doped into ZnO and all films crystallize in the hexagonal wurtzite structure with a preferred c-axis orientation. The lattice constants of Hf_xZn_1−xO films increase with the Hf contents. Two ultraviolet peaks centered at about 364 and 380 nm coexist in the fluorescent spectra. With increasing the Hf contents, the intensity of fluorescent peaks enhances remarkably. At the same time the energy gaps gradually increase, while the positions of ultraviolet peaks remain unchanged. The mechanism of luminescent emission for Hf_xZn_1−xO films was discussed.     

Influence of Co doping content on its valence state in Zn1−xCoxO (0 ≤ x ≤ 0.15) thin films

Zn_1−xCo_xO (0 ≤ x ≤ 0.15) thin films grown on Si (1 0 0) substrates were prepared by a sol-gel technique. The effects of Co doped on the structural, optical properties and surface chemical valence states of the Zn_1−xCo_xO (0 ≤ x ≤ 0.15) films were investigated by X-ray diffraction (XRD), ultraviolet-visible spectrometer and X-ray photoelectron spectroscopy (XPS). XRD results show that the Zn_1−xCo_xO films retained a hexagonal crystal structure of ZnO with better c-axis preferred orientation compared to the undoped ZnO films. The optical absorption spectra suggest that the optical band-gap of the Zn_1−xCo_xO thin films varied from 3.26 to 2.79 eV with increasing Co content from x = 0 to x = 0.15. XPS studies show the possible oxidation states of Co in Zn_1−xCo_xO (0 ≤ x ≤ 0.05), Zn_0.90Co_0.10O and Zn_0.85Co_0.15O are CoO, Co₃O₄ and Co₂O₃, with an increase of Co content, respectively.     

Structural, chemical and magnetic investigations of polycrystalline Zn1−xMnxO

Present study reports the detailed structural and magnetic, as well as chemical analysis of polycrystalline Zn_1−xMn_xO (where x=0, 0.005, 0.01, 0.03, 0.05 and 0.1) samples synthesized by the high-temperature solid state reaction route. X-ray diffraction studies reveal the presence of secondary phase for higher Mn-doping concentrations (x≥0.03). Secondary phase formation having spinel structure is confirmed and reported as an evidence for the first time using transmission electron microscopy study. Chemical investigations using X-ray photoelectron spectroscopy showed the presence of Mn in two valence states. From the observed results we are of the opinion that Zn²⁺ ions, mainly present at or near grain boundaries, diffuse into manganese oxide to form a stable spinel phase Zn_xMn_3−xO₄ at or near the grain boundaries of ZnO/Zn_1−xMn_xO. Magnetization measurements did not show any magnetic transition down to 5 K.     

Effects of Mn‐doping on surface acoustic wave properties of ZnO films

Surface acoustic wave (SAW) filters based on Mn‐doped ZnO films have been fabricated and effects of Mn‐doping on SAW properties are investigated. It is found that the electromechanical coupling coefficient (K²) of Zn_0.913Mn_0.087O films is 0.73 ± 0.02%, which is 73.8% larger than that of undoped ZnO films (0.42 ± 0.02%). Zn_0.913Mn_0.087O film filters also exhibit a lower absolute value of insertion loss (|IL|) of 16.1 dB and larger bandwidth (BW) of 5.9 MHz compared with that of undoped ZnO film filter. However, Zn_0.952Mn_0.048O film filters exhibit a smaller K² of 0.34 ± 0.02%, larger |IL| of 26.9 dB and smaller BW of 3.5 MHz. It is suggested that the SAW properties can be improved by appropriate Mn‐doping and Mn–ZnO/Si multilayer structure with large d₃₃ is promising for wide‐band and low‐loss SAW applications. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Synthesis and magnetic properties of Zn1−xMnxO films prepared by the sol-gel method

We report on the ferromagnetic characteristics of Zn_1−xMn_xO films (x=0.1-0.3) prepared by the sol-gel method on silicon substrates using transmission electron microscopy (TEM), energy dispersive spectroscopy (EDS), X-ray diffractometry (XRD) and superconducting quantum interference device (SQUID) magnetometry at various temperatures. Magnetic measurement show that the Curie temperature (T_C) and the coercive field (H_C) were ∼39 K and ∼2100 Oe for the film of x=0.2, respectively. EDS and TEM measurements indicate that Mn content at the interface is significantly higher than that at the center of the Zn_0.8Mn_0.2O film showing the ratio, Zn:Mn:O≅1:12:15. This experimental evidence suggests that ferromagnetic precipitates containing manganese oxide may be responsible for the observed ferromagnetic behavior of the film.     

Nanoscratch study of Zn1−xMnxO heteroepitaxial layers

We investigated the nanotribological properties of Zn_1−xMn_xO epilayers (0 ≤ x ≤ 0.16) grown by molecular beam epitaxy (MBE) on sapphire substrates. The surface roughness and friction coefficient (μ) were analyzed by means of atomic force microscopy (AFM) and hysitron triboscope nanoindenter techniques.The nanoscratch system gave the μ value of the films ranging from 0.17 to 0.07 and the penetration depth value ranging 294-200 nm when the Mn content was increased from x = 0 to 0.16. The results strongly indicate that the scratch wear depth under constant load shows that higher Mn content leads to Zn_1−xMn_xO epilayers with higher shear resistance, which enhances the Mn-O bond. These findings reveal that the role of Mn content on the growth of Zn_1−xMn_xO epilayers can be identified by their nanotribological behavior.     

No room temperature ferromagnetism in Mn over-doped Zn1−xMnxO (x>0.02)

Mn-doped ZnO samples having composition Zn_1−xMn_xO (x=0.02, 0.04 and 0.05) were synthesized by solid state reaction technique with varying concentration of Mn from 0.02 to 0.05. Evidence of room temperature ferromagnetism was observed only in the composition Zn_0.98Mn_0.02O sintered at 500 °C. Our XRD pattern confirms the presence of Mn₃O₄ impurity phase in all the Zn_1−xMn_xO samples with the exception of Zn_0.98Mn_0.02O. We emphasize that the appearance of Mn₃O₄ phase in the system forbids the exchange type of interaction between the Mn ions and suppresses the ferromagnetism in all the Mn over-doped Zn_1−xMn_xO (x>0.02) system. SEM microstructure study also supports the interruption of exchange type of interaction inside the system with the increase in Mn concentration in the sample. Interestingly, for this particular composition, Zn_0.98Mn_0.02O sintered at 500 °C, glassy ferromagnetism type of transition is observed at low temperature. This type of transition is attributed to the formation of the oxides of Mn clusters at low temperature.     

Ferromagnetism of epitaxially grown CaRu1−xMxO3 (M=Ti, Mn) films

Epitaxial thin films of CaRu_1−xM_xO₃ (M=Ti, Mn) were fabricated on a (0 0 1)-SrTiO₃ substrate by spin-coat method using organometallic solutions (metal alkoxides). Results of X-ray diffraction and transmission electron microscopy indicate that the epitaxial films were grown pseudomorphically so as to align the [0 0 l] axis of the CaRu_1−xM_xO₃ films perpendicular to the (0 0 1) plane of the SrTiO₃ substrate. Ferromagnetism and metal-insulator transition are induced by the substitution of transition metal ions. The occurrence of ferromagnetism was explained qualitatively assuming a TiRu₆ cluster model for CaRu_1−xTi_xO₃ film and a mixed valence model for CaRu_1−xMn_xO₃ film. Ferromagnetism was also observed for layered CaRuO₃/CaMnO₃ film and CaRuO₃/CaMnO₃/CaRuO₃/CaMnO₃ multilayer film and the magnetism was explained by an interfacial exchange interaction model with magnetic Mn³⁺, Mn⁴⁺, and Ru⁵⁺ ions.     

Room-temperature ferromagnetism in Sn1−xMnxO2 nanocrystalline thin films prepared by ultrasonic spray pyrolysis

Sn_1−xMn_xO₂ (x=0.01-0.05) thin films were synthesized on quartz substrate using an inexpensive ultrasonic spray pyrolysis technique. The influence of doping concentration and substrate temperature on structural and magnetic properties of Sn_1−xMn_xO₂ thin films was systematically investigated. X-ray diffraction (XRD) studies of these films reflect that the Mn³⁺ ions have substituted Sn⁴⁺ ions without changing the tetragonal rutile structure of pure SnO₂. A linear increase in c-axis lattice constant has been observed with corresponding increase in Mn concentration. No impurity phase was detected in XRD patterns even after doping 5 at% of Mn. A systematic change in magnetic behavior from ferromagnetic to paramagnetic was observed with increase in substrate temperature from 500 to 700 °C for Sn_1−xMn_xO₂ (x=0.01) films. Magnetic studies reveal room-temperature ferromagnetism (RTFM) with 3.61×10⁻⁴ emu saturation magnetization and 92 Oe coercivity in case of Sn_1−xMn_xO₂ (x=0.01) films deposited at 500 °C. However, paramagnetic behavior was observed for the films deposited at a higher substrate temperature of 700 °C. The presence of room-temperature ferromagnetism in these films was observed to have an intrinsic origin and could be obtained by controlling the substrate temperature and Mn doping concentration.     

Magnetic behavior of MnAs precipitates in Ga1−xMnxAs diluted magnetic semiconductor

Ferromagnetic Ga_1−xMn_xAs layers (where x≈4.7–5.5%) were grown on (1 0 0) GaAs substrates by molecular beam epitaxy. These p-type (Ga,Mn)As films were revealed to have a ferromagnetic structure and ferromagnetism is observed up to a Curie temperature of 318 K, which is ascribed to the presence of MnAs secondary magnetic phases within the film. It is highly likely that the phase segregation occurs due to the high Mn cell temperature around 890–920 °C, as it is well established that GaMnAs is unstable at such a high temperature. The MnAs precipitate in the samples with x≈4.7–5.5% has a Curie temperature T_c≈318 K, which was characterized from field-cooled and zero-field-cooled magnetization curves.     

Structural, magnetic and electronic transport properties of MnxGe1−x/Ge(0 0 1) films grown by MBE at 350 °C

We report on the structural, magnetic and electronic transport properties of thin Mn_xGe_1−x films grown at 350 °C. Isolated Mn₅Ge₃ nanoclusters, about 100 nm in size, were formed at the top surface of the film, dominating the magnetic properties of the whole film. Electronic transport properties show Mn doping effect indicating the presence of substitutional Mn ions dispersed in the Ge host, contributing to the formation of a Mn_xGe_1−x diluted phase. Electrical behaviour indicates a saturation effect with the raise of the nominal Mn concentration in the film, above x ≅ 0.03.     

Ferromagnetism in MnxGe1−x films prepared by magnetron sputtering

Mn_xGe_1−x thin films were prepared by magnetron sputtering with a substrate temperature of 673 K and subsequently annealed at 873 K. The X-ray diffraction (XRD) measurements showed that all samples had a single Ge cubic structure. No films showed clear magnetic domain structure under a magnetic force microscope (MFM). Atom force microscope (AFM) measurements showed that the films had an uniform particle size distribution, and a columnar growth pattern. X-ray photoelectron spectroscopy (XPS) measurements indicated that the valences of both Mn and Ge atoms increase with the Mn concentration. The resistance decreased with increasing temperature, suggesting that the films were typical semiconductors. Magnetic measurements carried out using a Physical Property Measurement System (PPMS) showed that all samples exhibited ferromagnetism at room temperature. There was a small concentration of Mn₁₁Ge₈ in the films, but the ferromagnetism was mainly induced by Mn substitution for Ge site.     

Growth and magnetism in amorphous Si1−xMnx thin films grown by thermal deposition

Si_1−xMn_x   (x?0.22$x?0.22$) thin films were grown by using a thermal evaporator, and their magnetic and electrical properties were investigated. The Si_1−xMn_x semiconductors are amorphous when Mn concentration is 9.0 at% and less. The electrical resistivities of amorphous Si_1−xMn_x   (x?0.09$x?0.09$) semiconductor thin films are in the range of 9.86–6.59×10⁻⁴ Ω cm at room temperature and decrease with increasing Mn concentration. The amorphous Si_1−xMn_x   (x?0.09$x?0.09$) semiconductor thin films are p-type and hole densities are 3.73×10¹⁸–1.33×10²² cm⁻³ at room temperature. Low temperature magnetization characteristics reveal that amorphous Si_1−xMn_x   (x?0.09$x?0.09$) semiconductor thin films are paramagnetic.     

Enhancement of initial permeability due to Mn substitution in polycrystalline Ni0.50−xMnxZn0.50Fe2O4

The structural and magnetic properties of Mn substituted Ni_0.50−xMn_xZn_0.50Fe₂O₄ (where x=0.00, 0.10 and 0.20) sintered at various temperatures have been investigated thoroughly. The lattice parameter, average grain size and initial permeability increase with Mn substitution. Both bulk density and initial permeability increase with increasing sintering temperature from 1250 to 1300 °C and above 1300 °C they decrease. The Ni_0.30Mn_0.20Zn_0.50Fe₂O₄ sintered at 1300 °C shows the highest relative quality factor and highest initial permeability among the studied samples. The initial permeability strongly depends on average grain size and intragranular porosity. From the magnetization as a function of applied magnetic field, M(H), it is clear that at room temperature all samples are in ferrimagnetic state. The number of Bohr magneton, n(μ_B), and Neel temperature, T_N, decrease with increasing Mn substitution. It is found that Mn substitution in Ni_0.50−xMn_xZn_0.50Fe₂O₄ (where x=0.20) decreases the Neel temperature by 25% but increases the initial permeability by 76%. Possible explanation for the observed characteristics of microstructure, initial permeability, DC magnetization and Neel temperature of the studied samples are discussed.     

BiFeO3/Zn1−xMnxO bilayered thin films

BiFeO₃/Zn_1−xMn_xO (x = 0-0.08) bilayered thin films were deposited on the SrRuO₃/Pt/TiO₂/SiO₂/Si(1 0 0) substrates by radio frequency sputtering. A highly (1 1 0) orientation was induced for BiFeO₃/Zn_1−xMn_xO. BiFeO₃/Zn_1−xMn_xO thin films demonstrate diode-like and resistive hysteresis behavior. A remanent polarization in the range of 2P_r ∼ 121.0-130.6 μC/cm² was measured for BiFeO₃/Zn_1−xMn_xO. BiFeO₃/Zn_1−xMn_xO (x = 0.04) bilayer exhibits a highest M_s value of ∼15.2 emu/cm³, owing to the presence of the magnetic Zn_0.96Mn_0.04O layer with an enhanced M_s value.     

Structural and magnetic properties of Mg(In2−xMnx)O4 system

We synthesized the Mn-doped Mg(In_2−xMn_x)O₄ oxides with 0.03?x?0.55 using a solid-state reaction method. The X-ray diffraction patterns of the samples were in a good agreement with that of a distorted orthorhombic spinel phase. Their lattice parameters and unit-cell volumes decrease with x due to the substitution of the smaller Mn³⁺ ions to the larger In³⁺ ions. The undoped MgIn₂O₄ oxide presents diamagnetic signals for 5 K?T?300 K. The M(H) at T=300 K reveals a fairly negative-sloped linear relationship. Neither magnetic hysteresis nor saturation behavior was observed in this parent sample. For the Mn-doped samples, however, positive magnetization were observed between 5 and 300 K even if the x value is as low as 0.03. The mass susceptibility enhances with Mn content and it reaches the highest value of 1.4×10⁻³ emu/g Oe (at T=300 K) at x=0.45. Furthermore, the Mn-doped oxides with x=0.06 and 0.2, respectively, exhibit nonlinear magnetization curves and small hysteretic loops in low magnetic fields. Susceptibilities of the Mn-doped samples are much higher than those of MnO₂, Mn₂O₃ oxides, and Mn metals. These results show that the oxides have potential to be magnetic semiconductors.     

Ferromagnetism in amorphous Ge1−xMnx grown by low temperature vapor deposition

Magnetic properties of amorphous Ge_1−xMn_x thin films were investigated. The thin films were grown at 373 K on (100) Si wafers by using a thermal evaporator. Growth rate was ∼35 nm/min and average film thickness was around 500 nm. The electrical resistivities of Ge_1−xMn_x thin films are 5.0×10⁻⁴∼100 Ω cm at room temperature and decrease with increasing Mn concentration. Low temperature magnetization characteristics and magnetic hysteresis loops measured at various temperatures show that the amorphous Ge_1−xMn_x thin films are ferromagnetic but the ferromagnetic magnetizations are changing gradually into paramagnetic as increasing temperature. Curie temperature and saturation magnetization vary with Mn concentration. Curie temperature of the deposited films is 80-160 K, and saturation magnetization is 35-100 emu/cc at 5 K. Hall effect measurement at room temperature shows the amorphous Ge_1−xMn_x thin films have p-type carrier and hole densities are in the range from 7×10¹⁷ to 2×10²² cm⁻³.     

Effect of indium incorporation in Zn1−xCoxO thin films

In the present paper, the preliminary investigations of a series of ZnO thin films co-doped with indium and cobalt with an objective to elucidate the correlation, if any, between the carrier concentration and the induced room temperature ferromagnetism (RTFM), are presented. The single-phasic (Zn_99.5In_0.5)_1−xCo_xO thin films are deposited by spray pyrolysis. The substitution of Zn²⁺ by Co²⁺ has been established by optical transmission analysis of these films. The films are ferromagnetic at room temperature; and the magnetization has higher value for indium and cobalt co-doped thin film as compared with Zn0₉₀Co_0.1O thin film (having no indium).