Effect of annealing on the characteristics of Au layers grown on the high-temperature deposited Ni50Fe50 layers

80 nm-thick Ni₅₀Fe₅₀ layers were sputter-deposited on glass substrates at 400 °C and then Au layers were sputter-deposited on the Ni₅₀Fe₅₀ layers. The Au/Ni₅₀Fe₅₀ bilayer films were annealed in a vacuum of 5×10⁻⁴ Pa from 250 to 450 °C for 30 min or 90 min. The characteristics of the Au layers were studied by Auger electron spectroscopy, field emission scanning electron microscopy, X-ray diffraction and a four-point probe technique. When the annealing temperature reaches 450 °C, Fe and Ni atoms diffuse markedly into the Au layer and the Fe content is more than the Ni content. When the annealing temperature is lower than 450 °C, the grain size of the Au layers does not change markedly with annealing temperature. However, as the annealing temperature reaches 450 °C, the annealing promotes the grain growth of the Au layer. As the annealing temperature exceeds 300 °C, the resistivity of the bilayer films increases with increasing annealing temperature. The diffusion of Fe and Ni atoms into the Au layer results in an increase in the resistivity of the annealed bilayer film. Large numbers of Fe and Ni atoms diffusing into the Au layer of the annealed Au/Ni₅₀Fe₅₀ bilayer film lead to a significant decrease in the lattice constant of the Au layer.     

Characteristics of NixFe100−x films deposited on SiO2/Si(1 0 0) by DC magnetron co-sputtering

Ni_xFe_100−x films with a thickness of about 200 nm were deposited on SiO₂/Si(1 0 0) substrates at room temperature by DC magnetron co-sputtering using both Fe and Ni₈₀Fe₂₀ targets. Compositional, structural, electrical and magnetic properties of the films were investigated. Ni₇₆Fe₂₄, Ni₆₅Fe₃₅, Ni₆₀Fe₄₀, Ni₅₅Fe₄₅, Ni₄₉Fe₅₁ films are obtained by increasing the sputtering power of the Fe target. All the films have a fcc structure. Ni₇₆Fe₂₄, Ni₆₅Fe₃₅, Ni₆₀Fe₄₀ and Ni₅₅Fe₄₅ films grow with crystalline orientations of [1 1 1] and [2 2 0] in the direction of the film growth while the Ni₄₉Fe₅₁ film has the [1 1 1] texture structure in the direction of the film growth. The lattice constant of the film increases linearly with increasing Fe content. All of the films grow with thin columnar grains and have void networks in the grain boundaries. The grain size does not change markedly with the composition of the film. The resistivity of the film increases with increasing Fe content and is one order of magnitude larger than that of the bulk. For all the films the magnetic hysteresis loop shows a hard magnetization. The Ni₇₆Fe₂₄ film has the lowest saturation magnetization of 6.75×10⁻² T and the lowest saturation field of 8.36×10⁴ A/m while the Ni₄₉Fe₅₁ film has a largest saturation magnetization of 9.25×10⁻² T and the largest saturation field of 1.43×10⁵ A/m.     

Growth and magnetic properties of ultrathin Ni1 + xFe2 − xO4 films for spin filter junctions

We investigated the spin filter effect in tunnel junctions with a Ni_1 + xFe_2 − xO₄ ferrimagnetic tunnel barrier. For higher T_c above room temperature, Ni_1 + xFe_2 − xO₄ film should be thicker than 4.0 nm and grown above 400 °C. The spin filter junctions (SFJs) of Fe₃O₄(001)/Ni_1 + xFe_2 − xO₄(001)/Al₂O₃/Fe/Au grown on MgO(001) substrates exhibited an inverse magnetoresistance effect at room temperature, which is consistent with the band calculation of NiFe₂O₄.     

Structure, magnetic and electrical transport properties of (Fe3O4)100 − xPtx composite films

Structure, magnetic and electrical transport properties of the polycrystalline (Fe₃O₄)_100 − xPt_x composite films fabricated using DC reactive magnetron sputtering at ambient temperature were investigated systematically. It is found that the films are composed of inverse-spinel-structured polycrystalline Fe₃O₄ and Pt. Pt addition proves the growth of Fe₃O₄ grains with the (111) orientation. All the films are ferromagnetic at room temperature. The dominant magnetic reversal mechanism turns from domain wall motion to Stoner-Wohlfarth rotation with the increasing x. The electrical transport mechanism also changes with the increasing x because Pt addition decreases the height of the tunneling barrier at the Fe₃O₄ grain boundaries, and makes the magnetoresistance of the films decrease.     

Epitaxial growth and exchange coupling of spinel ferrimagnet Ni0.3Zn0.7Fe2O4 on multiferroic BiFeO3

Thin films of the zinc nickel ferrite, Zn_0.7Ni_0.3Fe₂O₄ (ZNFO), were deposited by the RF magnetron sputtering on a number of substrates, including (001) oriented single crystals of LaAlO₃ (LAO) and SrTiO₃ (STO), polycrystalline Pt/Si, and epitaxial films of BiFeO₃ (BFO) and LaNiO₃ (LNO). Except for the films on Pt/Si, the ZNFO films grown on other substrates were epitaxial and their magnetic properties were affected by the heteroepitaxy induced strains. Typically, the coercivity (H_c) was increased with the strain, i.e. H_c varied from 31 Oe for the 150 nm thick polycrystalline films grown on Pt/Si, to 55 Oe and 155 Oe for the 20 nm thick epitaxial films grown on BFO and LAO, respectively. The saturation magnetization of the epitaxial films was reduced accordingly to about 470 emu/cm³ from 986 emu/cm³ in the polycrystalline films. The all-oxide architecture allowed field-annealing to perform at the temperature above the Neel temperature of BFO (~ 370 °C), after which clear exchange bias was observed.     

Synthesis and electrochemical properties of Ti doped Li3 − xFe2 − xTix(PO4)3/C cathode materials

Li_3 − xFe_2 − xTi_x(PO₄)₃/C (x = 0-0.4) cathodes designed with Fe doped by Ti was studied. Both Li₃Fe₂(PO₄)₃/C (x = 0) and Li_2.8Fe_1.8Ti_0.2(PO₄)₃/C (x = 0.2) possess two plateau potentials of Fe³⁺/Fe²⁺ couple (around 2.8 V and 2.7 V vs. Li⁺/Li) upon discharge observed from galvanostatic charge/discharge and cyclic voltammetry. Li_2.8Fe_1.8Ti_0.2(PO₄)₃/C has higher reversibility and better capacity retention than that of the undoped Li₃Fe₂(PO₄)₃/C. A much higher specific capacity of 122.3 mAh/g was obtained at C/20 in the first cycle, approaching the theoretical capacity of 128 mAh/g, and a capacity of 100.1 mAh/g was held at C/2 after the 20th cycle.     

Annealing effects on microstructure and mechanical properties of sputtered multilayer Cr(1 − x)AlxN films

Multilayer Cr_(1 − x)Al_xN films with a total thickness of 2 μm were deposited on high-speed steel by medium frequency magnetron sputtering from Cr and Al-Cr (70 at.% Al) targets. The samples were annealed in air at 400 °C, 600 °C, 800 °C and 1000 °C for 1 hour. Films were characterized by cross-sectional scanning electron microscopy and X-ray diffraction analysis. The grain size of the as-deposited multilayer films is about 10 nm, increasing with the annealing temperature up to 100 nm. Interfacial reactions have clearly changed at elevated annealing temperatures. As-deposited films' hardness measured by nanoindentation is 22.6 GPa, which increases to 26.7 GPa when the annealing temperature goes up to 400 and 600 °C, but hardness decreases to 21.2 GPa with further annealing temperature increase from 600 to 1000 °C. The multilayer film adhesion was measured by means of the scratch test combined with acoustic emission for detecting the fracture load. The critical normal load decreased from 49.7 N for the as-deposited films to 21.2 N for the films annealed at 1000 °C.     

Self-controlled growth of Fe3BO6 crystallites in shape of nanorods from iron-borate glass of small templates

Fe₃BO₆ can be an ideal compound for devising functional magnetic and dielectric properties in a single material for multiple applications such as electrodes, gas sensors, or medical tools. Useful to tailor such properties, here we report on a self-controlled Fe₃BO₆ growth in a specific shape of nanorods from a supercooled liquid precursor (an inorganic polymeric liquid or glass) of an initial composition (100 − x)B₂O₃ − xFe₂O₃, x = 40–50 mol%. B₂O₃ as a strong glass former co-bridges the Fe³⁺ ions in oxygen polygons primarily in a 2-D interconnected polymer network so that it dictates preferably a 1-D directional growth on the reaction Fe³⁺ species in form of a compound Fe₃BO₆, a favorable phase to nucleate and grow when annealing a precursor at 500–800 °C in ambient air. Distinct nanorods with a diameter ∼200 nm and 40–100 μm length have been formed on 10–15 min annealing a sample in microwave at moderate temperature 550 °C. A bonded surface B₂O₃ layer (15–25 nm thickness) has grown on the Fe₃BO₆ of the nanorods in situ in a specific structure. XPS bands in the Fe³⁺, B³⁺ and O²⁻ species confer this model structure. A local BO₃ → BO₄ conversion has incurred in the boroxol (B₃O_4.5)_n, n → ∞, rings in the surface layer, showing three distinct IR bands at 1035, 1215 and 1425 cm⁻¹.     

Enhanced ferromagnetic properties of multiferroic BiCoxFe1 − xO3 synthesized by hydrothermal method

The BiCo_xFe_1 − xO₃ samples have been successfully synthesized by hydrothermal process. The resulting products were characterized by X-ray powder diffraction (XRD), energy dispersive X-ray (EDS), differential thermal analysis (DTA), and physical property measurement system (PPMS).It was found that the magnetization of the obtained products was greatly enhanced by Co substituting for Fe ions. Furthermore, the value of magnetism of BiCo_xFe_1 − xO₃ samples can be adjusted by Fe doping concentration. DTA curve indicates the ferroelectric properties of the obtained BCFO samples are not affected by Co substitution. Therefore, it would be interesting to realize thin films with similar compositions and study their properties in the interest of device applications.     

Effect of chromium substitution on structure and magnetic properties of Bi2Fe4O9

Orthorhombic Bi₂Fe_4 − xCr_xO₉ (x = 0.0, 0.25, and 0.75) nanoplatelets were synthesized by a simple hydrothermal method. The structure, morphology, and magnetic properties of the obtained powders have been characterized. Calculation of the lattice parameters of Bi₂Fe_4 − xCr_xO₉, as well as bond lengths and angles, was carried out by X-ray diffraction Rietveld refinement. The volumes of the metal-oxygen tetrahedra and octahedra were calculated to be sequentially increasing as the Cr doping level increases. The samples undergo an antiferromagnetic transition at 250 ± 5 K. The magnetic moments of the samples increase with higher Cr doping level. The 3d electron spin state for Fe³⁺ in the as-prepared samples is different, which is possibly due to the distortion of Fe-O tetrahedra and octahedra in the crystal structure after chromium substitution.     

Deposition and characterization of pulsed direct current magnetron sputtered Al95.5Cr2.5Si2 (N1 − xOx) thin films

Aluminum rich oxynitride thin films were prepared using pulsed direct current (DC) magnetron sputtering from an Al_95.5Cr_2.5Si₂ (at.%) target. Two series of films were deposited at 400 °C and 650 °C by changing the O₂/(O₂ + N₂) ratio in the reactive gas from 0% (pure nitrides) to 100% (pure oxides). The films were investigated by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM) and nanoindentation. The results showed the existence of three different regions of microstructure and properties with respect to the oxygen concentration. For the samples deposited at 650 °C in the nitrogen rich region (O₂/(O₂ + N₂) ≤ 0.08), the formation of the h-AlN (002) and Al-N bond were confirmed by XRD and XPS measurements. The hardness of the films was around 30 GPa. In the intermediate region (0.08 ≤ O₂/(O₂ + N₂) ≤ 0.24), the presence of an amorphous structure and the shifting of the binding energies to lower values corresponding to non-stoichiometric compounds were observed and the hardness decreased to 12 GPa. The lowering of mechanical properties was attributed to the transition of the clean target to the reacted target under non-steady state deposition conditions. In the oxygen rich region (0.24 ≤ (O₂/(O₂ + N₂) ≤ 1), the existence of α-Al₂O₃-(113), α-Al₂O₃-(116) and Al-O bonds confirmed the domination of this phase in this region of deposition and the hardness increased again to 30-35 GPa. Films deposited at 400 °C showed the same behavior except in the oxygen rich region, where hardness remains low at about 12-14 GPa.     

Epitaxial growth of Fe3Si/CaF2/Fe3Si magnetic tunnel junction structures on CaF2/Si(111) by molecular beam epitaxy

The Fe₃Si(24 nm)/CaF₂(2 nm)/Fe₃Si(12 nm) magnetic tunnel junction (MTJ) structures were grown epitaxially on CaF₂/Si(111) by molecular beam epitaxy (MBE). The 12-nm-thick Fe₃Si underlayer was grown epitaxially on CaF_2/Si(111) at approximately 400 °C; however, the surface of the Fe₃Si film was very rough, and thus a lot of pinholes are considered to exist in the 2-nm-thick CaF₂ barrier layer. The average roughness (Ra) of the CaF₂ barrier layer was 7.8 nm. This problem was overcome by low-temperature deposition of Fe and Si at 80 °C on CaF₂/Si(111), followed by annealing at 250 °C for 30 min to form the Fe₃Si layer. The Ra roughness was significantly reduced down to approximately 0.26 nm. A hysteresis loop with coercive field H_c of approximately 25 Oe was obtained in the magnetic field dependence of Kerr rotation at room temperature (RT).     

Effect of LaNiO3 electrodes and lead oxide excess on chemical solution deposition derived Pb(Zrx,Ti1 − x)O3 films

The effects of LaNiO₃ (LNO) and Pt electrodes on the properties of Pb(Zr_x,Ti_1 − x)O₃ (PZT) films were compared. Both LNO and PZT were prepared by chemical solution deposition (CSD) methods. Specifically, the microstructure of LNO and its influence on the PZT properties were studied as a function of PbO excess. Conditions to minimize the Pyrochlore phase and porosity were found. Remnant polarization, coercive field and fatigue limit were improved in the PZT/LNO films relative to the PZT/Pt films. Additionally, the PZT crystallization temperature over LNO was 500 °C, about ~ 50 °C lower than over Pt. The crystallization temperature reported here is amongst the lowest values for CSD-based PZT films.     

Effects of Fe2O3 doping on the microstructure and piezoelectric properties of 0.55Pb(Ni1/3Nb2/3)O3-0.45Pb(Zr0.3Ti0.7)O3 ceramics

0.55Pb(Ni_1/3Nb_2/3)O₃-0.45Pb(Zr_0.3Ti_0.7)O₃(PNN-PZT) ceramics with different concentration of xFe₂O₃ doping (where x = 0.0, 0.8, 1.2, 1.6 mol%) were synthesized by the conventional solid state sintering technique. X-ray diffraction analysis reveals that all specimens are a pure perovskite phase without pyrochlore phase. The density and grain size of Fe-doped ceramics tend to increase slightly with increasing concentration of Fe₂O₃. Comparing with the undoped ceramics, the piezoelectric, ferroelectric and dielectric properties of the Fe-doped PNN-PZT specimens are significantly improved. Properties of the piezoelectric constant as high as d₃₃ ~ 956 pC/N, the electromechanical coupling factor k_p ~ 0.74, and the dielectric constant ε_r ~ 6095 are achieved for the specimen with 1.2 mol% Fe₂O₃ doping sintered at 1200 °C for 2 h.     

Tl2Ba2CaCu2O8 thin films on 2 in. LaAlO3(0 0 1) substrates

High quality Tl₂Ba₂CaCu₂O₈ (Tl-2212) superconducting thin films are prepared on both sides of 2 in. LaAlO₃(0 0 1) substrates by off-axis magnetron sputtering and post-annealing process. XRD measurements show that these films possess pure Tl-2212 phase with C-axis perpendicular to the substrate surface. The thickness unhomogeneity of the whole film on the 2 in. wafer is less than 5%. The superconducting transition temperatures T_cs of the films are around 105 K. At zero applied magnetic field, the critical current densities J_cs of the films on both sides of the wafer were measured to be above 2 × 10⁶ A/cm² at 77 K. The microwave surface resistance R_s of film was as low as 350 μΩ at 10 GHz and 77 K. In order to test the suitability of Tl-2212 thin films for passive microwave devices, 3-pole bandpass filters have been fabricated from double-sided Tl-2212 films on LaAlO₃ substrates.     

Si1 − xGex metal-oxide-semiconductor capacitors with HfTaOx gate dielectrics

Interfacial reactions and electrical properties of RF sputter deposited HfTaO_x high-k gate dielectric films on Si_1 − xGe_x (x = 19%) are investigated. X-ray photoelectron spectroscopic analyses indicate an interfacial layer containing GeO_x, Hf silicate, SiO_x (layer of Hf-Si-Ge-O) formation during deposition of HfTaO_x. No evidence of Ta-silicate or Ta incorporation was found at the interface. The crystallization temperature of HfTaO_x film is found to increase significantly after annealing beyond 500 °C (for 5 min) along with the incorporation of Ta. HfTaO_x films (with 18% Ta) remain amorphous up to about 500 °C anneal. Electrical characterization of post deposition annealed (in oxygen at 600 °C) samples showed; capacitance equivalent thickness of ~ 4.3-5.7 nm, hysteresis of 0.5-0.8 V, and interface state density = 1.2-3.8 × 10¹² cm^− 2 eV^− 1. The valence and conduction band offsets were determined from X-ray photoelectron spectroscopy spectra after careful analyses of the experimental data and removal of binding energy shift induced by differential charging phenomena occurring during X-ray photoelectron spectroscopic measurements. The valence and conduction band offsets were found to be 2.45 ± 0.05 and 2.31 ± 0.05 eV, respectively, and a band gap of 5.8 ± 05 eV was found for annealed samples.     

Effect of annealing temperature on magnetic property of Si1 − xCrx thin films

Polycrystalline Si_1 − xCr_x thin films have been prepared by magnetron sputtering followed by rapid thermal annealing (RTA) for crystallization. RTA was performed at 800 °C for 5 min, 1200 °C for 30 s and 1200 °C for 2 min, in a N₂ flow. The magnetic hysteresis loops were observed at room temperature in all the samples except for RTA at 800 °C for 5 min, and the annealing caused the decrease of saturation magnetization relative to the as-grown film. X-ray diffraction spectra and Raman spectra showed that the annealing process lead the deposited amorphous film to be crystallized and CrSi₂ phase formed. The magnetism of the films was determined by the competition between crystallinity and precipitation of diamagnetic CrSi₂ phase.     

Growth of La0.7Sr0.3MnO3 films on Si(0 0 1) using SrMnO3 template layer

Using RF magnetron sputtering, we have successfully grown (1 1 0) orientated La_0.7Sr_0.3MnO₃ (LSMO) films on Si(0 0 1) wafers using SrMnO₃ (SMO) as a template layer. The X-ray diffraction (XRD) patterns of the SMO/Si heterostructures indicate that SMO grows along the (1 1 0) orientation, the orientation relationship between the SMO thin film and the Si (0 0 1) substrate being given by (0 1 1)_SMO∣∣(0 0 1)_Si and [01]_SMO∣∣[0 1 0]_Si. From the XRD patterns of the LSMO/SMO/Si heterostructures, we find that with an increase of substrate temperature, the required thickness of SMO, which plays an effective role of tuning the preferential orientation of LSMO, will decrease at first and then increase. It is thought that this originates from the fact that the crystallization of SMO is not perfect at low temperatures whereas too high a temperature results in reaction and diffusion at the interface of the two layers.     

Magnetic properties and microstructures of single-layered Fe100 − xPtx films deposited onto heated substrates

The single-layered Fe_100 − xPt_x films of 30 nm thick with Pt contents (x) of 35-57 at.% are deposited on heated Si (100) substrate at a temperature (Ts) of 620 °C by magnetron co-sputtering. When the Pt content in the Fe-Pt alloy film is 35 at.%, the value of in-plane coercivity (Hc_//) is close to perpendicular coercivity (Hc_⊥) and both values are about 800 kA/m. The FePt films exhibit perpendicular magnetic anisotropy when the Pt content increases to the values of between 45 and 51 at.%. The perpendicular coercivity, saturation magnetization (Ms) and perpendicular squareness (S_⊥) for Fe₅₄Pt₄₆ film are as high as 1113 kA/m, 0.594 Wb/m² and 0.96, respectively. These magnetic properties reveal its significant potential as perpendicular magnetic recording media. Upon further increasing the Pt content to 57 at.%, the coercivity of the Fe-Pt film decreases drastically to below 230 kA/m and tends to be closer to in-plane magnetic anisotropy.     

New heat generation material in AC magnetic field for Y3Fe5O12-based powder material synthesized by reverse coprecipitation method

We found the most promising powder material for the application of the thermal coagulation therapy for the treatment of cancerous tissues. The maximum heat generation ability (ΔT = 40-77 °C, 370 kHz, 1.77 kA·m^− 1) was obtained for the powder materials by the calcination at 1100 °C for the Y_3 − XGd_XFe₅O₁₂ system. This ΔT value is higher than ca. ΔT = 30 °C in same magnetic field for fine FeFe₂O₄ particles as the candidate material for this type of therapy. The particle growth with the formation of the cubic single phase might influence to the high heat generation. As an unexpected result, the Gd₃Fe₅O₁₂ (X = 3) has no heat generation ability in an AC magnetic field.