Oxygen vacancies effects on phase diagram of epitaxial La<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> thin films

We investigated the effects of oxygen vacancies on the structural, magnetic, and transport properties of La_1–x Sr _x MnO₃ (x=0.1, 0.2, 0.33, 0.4, and 0.5) grown around a critical point (without/with oxygen vacancies) under low oxygen pressure (10 Pa) and high oxygen pressure (40 Pa). We found that all films exhibit ferromagnetic behavior below the magnetic critical temperature, and that the films grown under low oxygen pressures have degraded magnetic properties with lower Curie temperatures and smaller magnetic moments. These results show that in epitaxial La_1–x Sr _x MnO₃ thin films, the magnetic and transport properties are very sensitive to doping concentration and oxygen vacancies. Phase diagrams of the films based on the doping concentration and oxygen vacancies were plotted and discussed.     

Formation of nanostructured ω-Al 7 Cu 2 Fe crystalline phase by the ball milling technique

Crystalline ω-Al₇Cu₂Fe bulk samples were prepared by arc furnace and then by means of milling, the average grain size of these samples is reduced to the nanometer scale. The structural and magnetic properties of the nanostructured ω-Al₇Cu₂Fe phase have been studied by X-ray diffraction employing Rietveld method, Mössbauer spectroscopy and vibrating sample magnetometry. The results indicate that the average grain size of the synthesized sample (ω-phase) rapidly decreases from 79 to 12 nm after 5 h of milling. Furthermore, the hyperfine parameters of the nanostructured samples are higher than the values for the bulk ω-phase. Magnetic measurements show a weak ferromagnetic behavior with M _s ?=?0.46 emu.g^???1 for the bulk ω-phase. After the milling process this value increases to M _s ?=?1.50 emu.g^???1 due to the formation and growth of a magnetic interstitial region after reducing the average grain size of the sample.     

Electrical properties and conduction mechanisms in La2/3Ca1/3MnO3 thin films prepared by pulsed laser deposition on different substrates

Perovskite manganite La_2/3Ca_1/3MnO₃ thin films were directly grown on MgO(100), Si(100) and glass substrates by pulsed laser deposition. From the XRD patterns, the films are found to be polycrystalline, single-phase orthorhombic. The metal–insulator transition temperature is 209 K for LCMO/MgO, 266 K for LCMO/Si and 231 K for film deposited on the glass substrate. The conduction mechanism in these films is investigated in different temperature regimes. Low-temperature resistivity data below the phase transition temperature (T _P) have been fitted with the relation \( \rho = \rho_{0} + \rho_{2} T^{2} + \rho_{4.5} T^{4.5} \) , indicating that the electron–electron scattering affects the conduction of these materials. The high-temperature resistivity data (T > T _P) were explained using variable-range hopping (VRH) and small-polaron hopping (SPH) models. Debye temperature values are 548 K for LCMO/Cg, 568 K for LCMO/Si and 508 K for LCMO/MgO thin films. In all thin films, the best fitting in the range of VRH is found for 3D dimension. The density of states near the Fermi level N (E _F) for LCMO/MgO is lower due to the prominent role of the grain boundary in LCMO/MgO and increase in bending of Mn–O–Mn bond angle, which decreases the double exchange coupling of Mn³⁺–O²–Mn⁴⁺ and in turn makes the LCMO/MgO sample less conducting as compared to the other films.     

Investigation of structure and magnetic characteristics of Ni-implanted AlGaN films

The structural, valence of elements and magnetic characteristics of Ni-implanted Al_0.5Ga_0.5N films, deposited on Al₂O₃ substrates by metalorganic chemical vapor deposition (MOCVD), were reported. Ni ions were implanted into Al_0.5Ga_0.5N films by Metal Vapor Arc (MEVVA) sources under the energy of 100 keV for 3 h. The films were annealed at 900 K in the furnace for the transference of Ni ions from interstitial sites to substitutional sites in AlGaN and activating the Ni³⁺ ions. Characterizations were carried out in situ using X-ray diffraction (XRD), X-ray photoemission spectroscopy (XPS) and Vibrating sample magnetometer (VSM), indicating that the films have wurtzite structure without forming a secondary phase after annealing. Ni ions were successfully implanted into substitutional sites of Al_0.5Ga_0.5N films and the chemical bonding states of Ni³⁺ is Ni–N. The apparent hysteresis loops prove the films exhibited ferromagnetism at 300 K. The room temperature (RT) M_s and H_c obtained were approximately 0.22 emu/g and 32.97 Oe, respectively. From the first-principles calculation, A total magnetic moment of 2.86 μB per supercell is calculated: the local magnetic moment of NiN₄ tetrahedron, 2.38 μB, makes the primary contribution. The doped Ni atom hybridizes with its four nearby N atoms in NiN₄ tetrahedron, then N atoms are spin polarized and couple with Ni atom with strong magnetization, which result in ferromagnetism. Therefore, the p-d exchange mechanism is responsible for ferromagnetism in Ni-doped AlGaN. It is expected that the room temperature ferromagnetic Ni-doped Al_0.5Ga_0.5N films can make it possible to the applications for the spin electric devices.     

Structural and magnetic characterization of LaSrMnO3 thin films deposited by laser ablation on MgO substrates

La_2/3Sr_1/3MnO_3?δ thin films were deposited by laser ablation on MgO substrates under low oxygen pressure cool down. Their structural and magnetic properties are presented. The magnetic and electrical resistivity measurements indicate a reduction of the Curie and the metal–insulator transition temperatures due to the formation of magnetic inhomogeneneous films, where clusters of a metallic phase are mixed in a magnetically disordered insulating matrix. By a low-angle X-ray reflectivity study we show that the thin films are chemically inhomogeneous with an oxygen deficiency in bulk of the film when compared with the film/air interfacial region.     

SnO2 thin films grown by pulsed Nd:YAG laser deposition

SnO₂ thin films have been deposited on glass substrates by pulsed Nd:YAG laser at different oxygen pressures, and the effects of oxygen pressure on the physical properties of SnO₂ films have been investigated. The films were deposited at substrate temperature of 500°C in oxygen partial pressure between 5.0 and 125 mTorr. The thin films deposited between 5.0 to 50 mTorr showed evidence of diffraction peaks, but increasing the oxygen pressure up to 100 mTorr, three diffraction peaks (110), (101) and (211) were observed containing the SnO₂ tetragonal structure. The electrical resistivity was very sensitive to the oxygen pressure. At 100 mTorr the films showed electrical resistivity of 4×10⁻² Ω cm, free carrier density of 1.03×10¹⁹ cm⁻³, mobility of 10.26 cm² V⁻¹ s⁻¹ with average visible transmittance of ∼87%, and optical band gap of 3.6 eV.     

‘In-situ’ ink-jet printed Fe-doped MgO thin films with tunable ferromagnetism

Magnetism in wide band gap materials is of great interests for future spintronic device applications. We prepared MgO and Fe-doped MgO films ‘in-situ’ on substrates by inkjet printing, and investigated the ferromagnetism tuned by the doping of Fe, the annealing temperature and the film thickness. It is found that the Fe-doping improves the crystallinity of the films with lattice structure changed by annealing temperature. The saturation magnetization (M_s) of the films enhanced by ~5 times comparing with the pure MgO thin film of similar thickness (~90 nm), because of both the long-range ordering of localized 3d electrons in Fe and the defects induced magnetism. The M_s at 5 K decreases with the film thickness, which is mainly attributed to the interface induced ferromagnetism. The Fe-doped MgO films with ferromagnetism in this work can be used in future spintronic devices.     

Ferromagnetism modulation by phase change in Mn-doped GeTe chalcogenide magnetic materials

In this work, an effective method to modulate the ferromagnetic properties of Mn-doped GeTe chalcogenide-based phase change materials is presented. The microstructure of the phase change magnetic material Ge_1?x Mn _x Te thin films was studied. The X-ray diffraction results demonstrate that the as-deposited films are amorphous, and the crystalline films are formed after annealing at 350 °C for 10 min. Crystallographic structure investigation shows the existence of some secondary magnetic phases. The lattice parameters of Ge_1?x Mn _x Te (x = 0.04, 0.12 and 0.15) thin films are found to be slightly different with changes of Mn compositions. The structural analysis clearly indicates that all the films have a stable rhombohedral face-centered cubic polycrystalline structure. The magnetic properties of the amorphous and crystalline Ge_0.96Mn_0.04Te were investigated. The measurements of magnetization (M) as a function of the magnetic field (H) show that both amorphous and crystalline phases of Ge_0.96Mn_0.04Te thin film are ferromagnetic and there is drastic variation between amorphous and crystalline states. The temperature (T) dependence of magnetizations at zero field cooling (ZFC) and field cooling (FC) conditions of the crystalline Ge_0.96Mn_0.04Te thin film under different applied magnetic fields were performed. The measured data at 100 and 300 Oe applied magnetic fields show large bifurcations in the ZFC and FC curves while on the 5,000 Oe magnetic field there is no deviation.     

Optimization of perpendicular magnetic anisotropy tips for high resolution magnetic force microscopy by micromagnetic simulations

Magnetic Force Microscopy (MFM) tip coated with perpendicular magnetic anisotropy film (PMA tip) is one of the choices for high resolution imaging at low scan height (SH), since it has negligible tip–sample interaction related to its stable magnetic state, sharp, and small tip stray field. In this work, detailed micromagnetic studies are carried out to understand the effect of geometrical and magnetic parameters including the cone angle θ of the PMA tip, intergrain exchange constant $A_{2}^{*}$ , saturation magnetization M _s and uniaxial crystalline anisotropy constant K ₁ of the tip coating on the MFM tip resolution. To evaluate the resolution performance of the optimized PMA tip, MFM images of high-density granular recording media and patterned media are simulated. We find that, for the PMA tip and its coating, a cone angle in a range of 36.9^° to 53.1^°, a saturation M _s of 700 emu/cm³, a large uniaxial crystalline anisotropy constant K ₁ (>4.9×10⁶ erg/cm³) and a high intergrain exchange constant $A_{2}^{*}$ of (0.3–1.0)×10^?6 erg/cm are optimized conditions for high resolution imaging. The optimized PMA tip has an excellent performance on imaging of high-density thin film media (bit size of 8×16 nm²) at low SH of 2–8 nm and bit pattern media with a pitch of 50 nm, edge-edge spacing of 5–15 nm at SH of 8–15 nm.     

Controlling the composition and the magnetic properties of hexagonal Co2Z ferrite powders synthesized using two different methods

Polycrystalline Co₂Z hexaferrite (Ba₃Co₂Fe₂₄O₄₁) powders have been prepared via two wet chemical routes: sol gel auto-combustion (SGA) and co-precipitation (CP) methods. The effects of synthesis conditions on the crystal structure, crystallite size, morphology, and magnetic properties were systematically studied. The results revealed that single Co₂Z hexaferrite phase was obtained at relatively low temperature 1250 ^°C for 5 h via the SGA method whereas it was formed at 1300 ^°C for 6 h using the CP pathway. The microstructures of the pure powders appeared as a hexagonal platelet-like structure. The particle size of the pure Co₂Z powders by CP method was higher than as obtained by the SGA method. The soft characteristic loops were obtained for single Co₂Z hexaferrite phase synthesized using both routes. High saturation magnetization (M _s =53.7 emu/g) was achieved for the Co₂Z powder synthesized via the CP method compared with the formed single phase synthesized via the SGA method (M _s =47.0 emu/g). Good dielectric and dynamic magnetic properties were obtained for the Co₂Z powder synthesized via the SGA method in comparison with the sample synthesized via CP method. The results obtained are discussed on the basis of electromagnetic theory.     

Magnetic properties of a Pt/Co2FeAl/MgO structure with perpendicular magnetic anisotropy

Microstructures and magnetic properties of Ta/Pt/Co 2 FeAl（CFA）/MgO multilayers are studied to understand perpendicular magnetic anisotropy（PMA） of half-metallic full-Heusler alloy films.PMA is realized in a 2.5-nm CFA film with B2-ordered structure observed by a high resolution transmission electron microscope.It is demonstrated that a high quality interface between the ferromagnetic layer and oxide layer is not essential for PMA.The conversions between in-plane anisotropy and PMA are investigated to study the dependence of magnetic moment on temperature.At the intersection points,the decreasing slope of the saturation magnetization（M s） changes because of the conversions.The dependence of M s on the annealing temperature and MgO thickness is also studied.     

Physical investigations on pulsed laser deposited nanocrystalline ZnO thin films

The nanocrystalline ZnO thin films were deposited by pulsed laser deposition on quartz and i-Si (100) substrates at different substrate temperatures (473 K–873 K) and at different mixed partial pressures (0.05, 0.01, and 0.5 mbar) of Ar+O₂. The structural studies from XRD spectra reveals that the films deposited at 0.05 mbar and at lower substrate temperatures were c-axis oriented with predominant (002) crystallographic orientation. At 873 K along with (002) orientation, additional crystallographic orientations were also observed in case of films deposited at 0.01 and 0.5 mbar pressures. The composition of Zinc and Oxygen in ZnO films from EDAX reveals that the films deposited at lower partial pressures were have high at.% of O₂ whereas higher partial pressures and substrate temperatures had high at.% Zn. The surface microstructure of the films show that the films deposited at lower partial pressures (0.05 mbar ) and at lower substrate temperatures (473 K) were found to have nanoparticles of size 15 nm where as films deposited at 873 K have nanorods. The length of these nanorods increases with increasing Ar+O₂ partial pressure to 0.5 mbar. The optical energy gap of the film deposited at lower partial pressure and substrate temperature was 3.3 eV and decrease with the increase of substrate temperatures. The films deposited at 0.5 mbar and at 873 K emitted an intense luminescence at a wavelength of 390 nm. The measured thickness of deposited films by spectroscopic ellipsometry is around 456 nm.     

Characterization of magnesium oxide gate insulators grown using RF sputtering for ZnO thin-film transistors

A ZnO thin-film transistor (TFT) with an MgO insulator was fabricated on a silicon (100) substrate using a radiofrequency magnetron sputtering system. The MgO insulator was deposited using the same deposition system; the total pressure during the deposition process was maintained at 5 mTorr, and the oxygen percentage of O₂/(Ar + O₂) was set at 30%, 50%, or 70%. The process temperature was maintained at below 300 °C. The dielectric constant of the MgO thin layer was approximately 11.35 with an oxygen percentage of 70%. This ZnO TFT displayed enhanced transistor properties, with a field-effect mobility of 0.0235 cm² V⁻¹ s⁻¹, an I_ON/I_OFF ratio of ∼10⁵, and an SS value of 1.18 V decade⁻¹; these properties were superior to those measured for the MgO insulators synthesized using oxygen percentages of 30% and 50%.     

Growth by laser ablation of Ti-based oxide films with different valency states

x La_2/3+yTiO_3-δ perovskite (with δ≤0.5) were deposited by the laser ablation technique from Li_0.33La_0.56TiO₃ targets. Their growth onto MgO substrateswas studied as a function of the oxygen pressure. For films grown in vacuum (10^-6 mbar), a La_0.63TiO_2.5 composition was obtained, meaning that Ti³⁺ alone is present in the films, while Li ions are not incorporated under these conditions. This material shows good electric conductivity (ρ=500 mΩ cm). By contrast, insulating films with a Li_0.1La_0.70TiO₃ composition corresponding to the Ti⁴⁺ species were obtained at high oxygen pressures (>0.05 mbar). For all conditions, textured films were grown with different orientations depending on the temperature and the oxygen pressure. Received: 10 September 1997/Accepted: 24 November 1997     

CEMS study on diluted magneto titanium oxide films prepared by pulsed laser deposition

6% ⁵⁷Fe doped titanium oxide films, prepared by pulsed laser deposition (PLD) on sapphire substrate at 650°C under various vacuum conditions, were characterized mainly by conversion electron Mössbauer spectrometry (CEMS). Two magnetic sextets with hyperfine fields 33 and 29 T, and one doublet were observed in the CEMS spectra of TiO₂ films prepared under PO₂ = 10^?6 and 10^?8 torr, which showed ferromagnetism at room temperature, whereas only the doublet of paramagnetic Fe³⁺ species was observed for the film prepared under PO₂ = 10^?1 torr.     

磁控溅射方法制备垂直取向FePt/BN颗粒膜

用磁控溅射在热单晶MgO(100)基片上制备了［FePt/BN］多层膜，经真空热处理后，得到具有垂直取向L1₀-FePt/BN颗粒膜.X射线衍射结果和磁性测量的结果表明，［FePt(2nm)/BN(0.5nm)］₁₀和［FePt(1nm)/BN(0.25nm)］₂₀多层膜经700℃热处理1h后，均具有较好的(001)取向.［FePt(1nm)/BN(0.25nm)］₂₀垂直矫顽力达到522kA/m，剩磁比达到0.99，开关场分布S达到0.94，FePt晶粒平均尺寸约15—20nm，适合用于将来超高密度的垂直磁记录介质. 关键词： 磁控溅射 垂直磁记录 0-FePt/BN纳米颗粒膜')" href="#">L1₀-FePt/BN纳米颗粒膜     

The effect of different chemical compositions caused by the variation of deposition potential on properties of Ni-Co films

The magnetic and microstructural properties of Ni-Co films electrodeposited at different cathode potentials were investigated. The compositional analysis revealed that the Ni content increases from 13 at.% to 44 at.% in the films with increasing deposition potential. Magnetic measurements showed that the saturation magnetization, M_s of the films decreased with increase of Ni content as the deposition potential increased. M_s values changed between 1160 emu/cm³ and 841 emu/cm³. The X-ray diffraction revealed that the crystalline structure of the films is a mixture of the predominant face-centered cubic (fcc) and hexagonal closed packed. However, the mixture phase turns to the fcc because of increasing Ni content up to 44 at.% at the highest (−1.9 V) potential by enhancing the intensity of reflections from the fcc phase. The changes observed in the magnetic and microstructural properties were ascribed to the changes observed in the chemical composition caused by the applied different deposition potentials.     

Effects of rapid thermal annealing on structural, magnetic and optical properties of Ni-doped ZnO thin films

XPS depth profiles were used to investigate the effects of rapid thermal annealing under varying conditions on the structural, magnetic and optical properties of Ni-doped ZnO thin films. Oxidization of metallic Ni from its metallic state to two-valence oxidation state occurred in the film annealed in air at 600 °C, while reduction of Ni²⁺ from its two-valence oxidation state to metallic state occurred in the film annealed in Ar at 600 and 800 °C. In addition, there appeared to be significant diffusion of Ni from the bottom to the top surface of the film during annealing in Ar at 800 °C. Both as-deposited and annealed thin films displayed obvious room temperature ferromagnetism (RTFM) which was from metallic Ni, Ni²⁺ or both with two distinct mechanisms. Furthermore, a significant improvement in saturation magnetization (M_s) in the films was observed after annealing in air (M_s = 0.036 μ_B/Ni) or Ar (M_s = 0.033 μ_B/Ni) at 600 °C compared to that in as-deposited film (M_s = 0.017 μ_B/Ni). An even higher M_s value was observed in the film annealed in Ar at 800 °C (M_s = 0.055 μ_B/Ni) compared to that at 600 °C mainly due to the diffusion of Ni. The ultraviolet emission of the Ni-doped ZnO thin film was restored during annealing in Ar at 800 °C, which was also attributed to the diffusion of Ni.     

Optical properties of nonstoichiometric ZrO<Subscript> <Emphasis Type="Italic">x</Emphasis> </Subscript> according to spectroellipsometry data

Amorphous nonstoichiometric ZrO_x films of different composition have been synthesized by the method of ion-beam sputtering deposition of metallic zirconium in the presence of oxygen at different partial oxygen pressures in the growth zone, and their optical properties have been studied in the spectral range of 1.12–4.96 eV. It is found that light-absorbing films with metallic conductivity are formed at the partial oxygen pressure below 1.04 × 10^–3 Pa and transparent films with dielectric conductivity are formed at the pressure above 1.50 × 10^–3 Pa. It is shown that the spectral dependences of optical constants of ZrO_x films are described well by the corresponding dispersion models: the Cauchy polynomial model for films with dielectric conductivity and the Lorentz–Drude oscillator model for films with metallic conductivity.