Enhancement of magnetoresistance sensitivity in Co/Cu/NiFe trilayers by softening the Co hard layer

Co/Cu/NiFe trilayers were prepared by sputtering without magnetic field applied. We have found that the Co(2 nm)Cu(1 nm)NiFe(2 nm) trilayer using Ta as buffer layer exhibits an enhanced magnetoresistance (MR) sensitivity by a factor of more than 6 and a low saturation field of 9.3 Oe. Experimental results have demonstrated that the low saturation field is attributed to the softening of the Co layer by depositing the Co(2 nm)Cu(1 nm)NiFe(2 nm) sandwich on Ta layer. The decrease of the coercivity of the Co layer also plays an important role in the enhancement of MR sensitivity by reducing the effective coercivity of the NiFe layer, which is discussed in terms of the change in interlayer coupling.     

Epitaxial growth La0.67Ca0.33MnO3 thin film by radio frequency sputtering method

Perfect epitaxial growth of La_0.67Ca_0.33MnO₃ (LCMO) thin film has been achieved on (1 0 0) LaAlO₃ (LAO) single crystal substrate by radio frequency sputtering method. X-ray diffraction (XRD) and electron diffraction analysis indicates that La_0.67Ca_0.33MnO₃ film grows epitaxially on LaAlO₃ along [1 0 0] direction of the substrate. The resistivity variation with temperature of the film shows a sharp metal to semiconductor transition peak around 253 K, which is close to that of the target. The magnetoresistance (MR) also reveals high quality epitaxy film characteristic at low temperatures and near the metal to semiconductor transition temperature.     

Microstructure and mechanical properties of CrN films fabricated by high power pulsed magnetron discharge plasma immersion ion implantation and deposition

CrN films with strong adhesion with the substrate have been fabricated on Ti6Al4V alloy using novel plasma immersion ion implantation and deposition (PIII&D) based on high power pulsed magnetron sputtering (HPPMS). A macro-particle free chromium plasma is generated by HPPMS while the samples are subjected to high voltage pulses to conduct PIII&D. The CrN coatings have a dense columnar structure and low surface roughness. The grains in the films have the face-center cubic (fcc) structure with the (2 0 0) preferred orientation. An excellent adhesion is achieved with a critical load up to 74.7 N. An implantation voltage of 18 kV yields a hardness of 18 GPa and better wear resistance and a low friction coefficient of 0.48 are achieved.     

Influence of superparamagnetic regions on the giant magnetoresistance of electrodeposited Co–Cu/Cu multilayers

The room-temperature magnetoresistance (MR) of electrodeposited Co–Cu/Cu multilayers was investigated. Samples were prepared on either a polycrystalline Ti foil or on a silicon wafer covered with a Ta buffer and a Cu-seed layer. The field dependence of the magnetoresistance was analyzed by decomposing the GMR into ferromagnetic (FM) and superparamagnetic (SPM) contributions, whereby the field dependence of the latter could be described by a Langevin function. In order to better understand the influence of the deposition conditions on the GMR in electrodeposited multilayers, the evolution of the relative importance of the two GMR contributions is discussed in terms of the Co dissolution process during the Cu deposition pulse.     

Seebeck and magnetoresistive effects of Ga-doped ZnO thin films prepared by RF magnetron sputtering

In this paper, Ga-doped ZnO (GZO) films were deposited on glass substrates at different substrate temperatures by RF magnetron sputtering. The effect of substrate temperature on the structural, surface morphological properties, Seebeck and magnetoresistive effects of GZO films was investigated. It is found that the GZO films are polycrystalline and preferentially in the [0 0 2] orientation, and the film deposited at 300 °C has an optimal crystal quality. Seebeck and magnetoresistive effects are apparently observed in GZO films. The thermoelectromotive forces are negative. Decreasing substrate temperature and annealing in N₂ flow can decrease carrier concentration. The absolute value of the Seebeck coefficient increases with decreasing carrier concentration. The maximal absolute value of Seebeck coefficient is 101.54 μV/K for the annealed samples deposited at the substrate temperature of 200 °C. The transverse magnetoresistance of GZO films is related to both the magnetic field intensity and the Hall mobility. The magnetoresistance increases almost linearly with magnetic field intensity, and the films deposited at higher substrate temperature have a stronger magnetoresistance under the same magnetic field, due to the larger Hall mobility.     

Surface anisotropy of CrxN1−x films prepared on an inner wall by magnetic sputtering

The Cr_xN_1−x films were prepared by magnetic sputtering on an inner wall of a column. Their surface morphologies were studied by atomic force microscopy (AFM) and found to be anisotropic. The 3-D AFM images indicate the grains grow upward along the rotational axis of the system. The AFM top views show a mosaic-like pattern for all samples. Analysis of the height-height correlation function demonstrates that correlation length along the rotational axis of the system is longer than that vertical to the axis. The correlation length and RMS roughness increase with the flow rate of N₂. A deposition model proposed that the shadowing effect of the reactive gas N₂ is the dominant factor for surface anisotropy. The bias added on the substrate is regarded to modulate the grain direction to the rotation axis and enhance roughness and defects.     

Titanium oxynitride thin films sputter deposited by the reactive gas pulsing process

DC reactive sputtering was used to successfully make thin films of titanium oxynitride using titanium metallic target, argon as plasma gas and nitrogen and oxygen as reactive gases. The nitrogen partial pressure was kept constant during every deposition whereas oxygen flow rate was pulsed using a square pattern. The study consisted in analysing the influence of the shape of the pulsed rate on physical properties of these films. In order to adjust the metalloid concentration to get films with a wide range of oxygen-to-nitrogen ratios, the reactive gas pulsing process (RGPP) was used. In this process, the oxygen flow switches “on” and “off” periodically according to a duty cycle α = t_ON/T. Electrical conductivity of films measured against temperature was gradually modified from metallic (σ_300K = 4.42 × 10⁴ S m⁻¹) to semi-conducting behaviour (σ_300K = 7.14 S m⁻¹) with an increasing duty cycle. Mechanical properties like nanohardness (H_n) and reduced Young's modulus (E_r) of the films were investigated. Experimental values of H_n and E_r obtained by nanoindentation at 10% depth ranged from 15.8 to 5.2 GPa and from 273 to 142 GPa, respectively. Evolutions of H_n and E against duty cycle were similar. A regular decrease was observed for duty cycle α ≤ 25% corresponding to the occurrence of TiO_xN_y phase. Higher duty cycles led to the smallest values of H_n and E and correlated with TiO₂ compound composition. At last, the colour variation of these titanium oxynitrides was investigated as a function of α in the L^*a^*b^* colour space. It was related to the chemical composition of the films.     

Growth of a textured quasicrystalline phase in Ti-Ni-Zr films prepared by pulsed laser deposition

The preparation in thin film form of the known icosahedral phase in Ti-Ni-Zr bulk alloys has been investigated as a function of substrate temperature. Films were deposited by pulsed laser deposition on sapphire substrates at temperatures ranging from room temperature to 350 °C. Morphological and structural modifications have been followed by grazing-incidence and θ–2θ X-ray diffraction, transmission electron diffraction and imaging. Chemical composition has been analyzed by electron probe microanalysis. The in-depth variation of composition has been studied by secondary neutral mass spectroscopy. We show that pulsed laser deposition at 275 °C makes the formation of a 1-μm-thick film of Ti-Ni-Zr quasicrystalline textured nanocrystallites possible. Received: 7 June 2001 / Accepted: 18 February 2002 / Published online: 3 June 2002 RID="*" ID="*"Corresponding author. Fax: +33-3/8357-6300, E-mail: brien@mines.u-nancy.fr     

Influence of Interface Structure of Co/Cu （100） Superlattices on Electronic Structure and Giant Magnetoresistance

Electronic structures and magnetoresistance （MR） of Co3 Cu5 and Co3 Cur models as well as their interface atom exchange models Co2 CuCoCu4 and Co2 CuCoCu6 are investigated by the tlrst-principles pseudopotential planewave method based on density functional theory. Charge transfer, magnetic moment, density of states, spin asymmetry factor, and MR ratio are discussed. The results show that the values of charge transfer and spin asymmetry factor at the Fermi level of Co layers are closely related to the neighbouring background of the Co layer. The Co layer with two sides adjacent to the Cu layer would transfer more charge to the Cu layer than other neighbouring background and have the largest spin asymmetry factor at the Fermi level. The Co layer with two neighbouring Co layers （interior Co） would gain a little charge and have the smallest spin asymmetry factor at the Fermi level. Two-current model is used to evaluate the MR ratio of Co2CuCoCu4 （Co2CuCoCu6） to be larger than that of Co3 Cu5 （Co3 CUT）, which can be explained by the charge transfer and spin asymmetry factor.     

Structural and dielectric properties of Bi4Ti3O12 thin films prepared by metalorganic solution deposition

Ferroelectric Bi₄Ti₃O₁₂ thin films with single phase and nanosized microstructure were prepared on Pt/Ti/SiO₂/Si(111) substrate by metalorganic solution deposition using titanium butoxide and bismuth nitrate at relatively low annealing temperatures. The internal strain in Bi₄Ti₃O₁₂ thin films was calculated from the peak shifts and broadening of XRD patterns. With increase in annealing temperature, the uniform strain decreased from positive to zero and then to negative, and the non-uniform strain decreased and was negative. The total strain was negative and in the range of -0.2%–-1.0%, from which the stress of the films was calculated to be about -1.4×10⁹ N/m². The mode values of strain decreased with increase in annealing temperature and increased with increase in film thickness. The dielectric constant increased with increase in annealing temperature and film thickness. The dielectric properties were interpreted by considering the influence of strain, grain size, and grain boundaries. The strain lowered the polarization and increased the dielectric constant. The larger the grain size and the thinner the grain boundary, the greater the dielectric constant. The influence of grain size and grain boundary was stronger than that of the strain. Received: 23 September 1998 / Accepted: 6 January 1999 / Published online: 24 March 1999     

Thin films of magnesium oxide prepared by plasma-enhanced chemical vapour deposition

Thin films of magnesium oxide have been deposited on glass, quartz, stainless steel, and nickel by plasma enhanced chemical vapour deposition using 2,2,6,6-tetramethyl-heptanedionato-3,5-magnesium(II) (Mg(thd)₂) as precursor. The films show (100)-orientation when deposited at temperatures 673 K. The influence of experimental parameters on deposition rate and film properties has been studied.On leave from the Beijing Solar Energy Research Institute, Beijing, China     

Influence of sputtering pressure on the giant magnetoresistance and structure in Fe–Cu–Ni granular thin films

Composition, structure and giant magnetoresistance in Fe_xCu_yNi_z films prepared at different sputtering pressures were investigated. X-ray diffraction studies showed only Cu (1 1 1) peak from the Cu grain. The shifts in the d-spacing d₁₁₁ of Cu indicates a progressive substitution of Ni in the Cu lattice. Similar trends in d₁₁₁ of Cu observed for the samples prepared at different sputtering pressures indicate that the structural behaviour of the samples is nearly independent of the sputtering pressure. A significant enhancement of magnetoresistance (MR) for the samples sputtered at 0.001 mbar as compared to that sputtered at 0.02 mbar is attributed to the reduced role of residual gas impurities in the films upon lowering the sputtering pressure. An interesting observation is that the MR did not significantly decrease even with a large substitution of Ni in the Cu grains.     

Thermochromic VO2 thin films synthesized by rf-inverted cylindrical magnetron sputtering

The novel physical vapor deposition called inverted cylindrical magnetron sputtering (also known as hollow cathode sputtering) is commonly used to coat wires, fibers, ribbons as well as all sides of three-dimensional substrates. It is a reproducible method for the production of nano-structured systems onto complex shapes substrates. This paper reports the first synthesis and feasibility of reliably reproduced stoichiometric pure textured VO₂ nano-structures by the rf-inverted cylindrical magnetron sputtering. Morphological, structural, elemental analysis and optical properties of synthesized VO₂ under optimized conditions are reported.     

Investigation of Ti/TiN multilayered films in a reactive mid-frequency dual-magnetron sputtering

Influence of the process parameters like (i) sputtering gas pressure, (ii) target current, (iii) substrate bias voltage and (iv) substrate temperature of a reactive mid-frequency dual-magnetron sputtering on (a) surface defects and (b) mechanical properties of Ti/TiN multilayered films was investigated. The forming mechanisms of the observed droplets and craters were analyzed. Results showed when: (1) pressure of Ar/N₂ gases PAr/N₂ was at 0.31 Pa and substrate temperature was in certain range, the size and the density of the surface defects on the TiN films tended to decrease with increasing the target current and the pulsed bias voltage; (2) the optimal deposition parameters for accomplishing fewer surface defects were used, increasing the thickness of the Ti buffer layer decreased the microhardness in certain level, and the adhesion was firstly increased and then decreased as thickness reaching and/or beyond a critical value. Results also showed that selection of optimized process parameters evidently minimized the surface defects and improved the mechanical properties of the film.     

Aluminium oxide thin films prepared by plasma-enhanced chemical vapour deposition

Thin films of aluminium oxide have been deposited on glass, quartz, Si(100), steel, nickel, and aluminium by plasma-enhanced chemical vapour deposition (PECVD) using aluminium acetylacetonate (Al(acac)₃) as precursor. The deposits are hard (up to 2370 HK) and show good adherence to the substrates. The influence of various experimental parameters on deposition rate, film composition and hardness has been studied. The bias turned out to be the most effective parameter.On leave from Beijing Solar Energy Research Institute, Beijing, P.R. China     

GMR in multilayered nanowires electrodeposited in track-etched polyester and polycarbonate membranes

Commercially available track-etched polyester membranes were used as templates to electrodeposit Co–Ni–Cu/Cu multilayered nanowires, giving room-temperature current perpendicular to plane (CPP) giant magnetoresistance (GMR) values of up to ∼12%. In contrast to similar nanowires electrodeposited in track-etched polycarbonate membranes, the GMR obtained in multilayered nanowires electrodeposited in the polyester membranes increased with decreasing Cu-layer thickness t_Cu, for t_Cu in the 2–7 nm range, indicating a lack of ferromagnetic coupling through pinholes, etc. Transmission electron micrographs showed clear evidence for smooth, parallel layer interfaces in the nanowires.     

Effects of experimental parameters on composition of boron carbon nitride thin films deposited by magnetron sputtering

We have synthesized boron carbon nitride thin films by radio frequency magnetron sputtering. The films structure and composition were characterized by X-ray diffraction, Fourier transform infrared spectroscopy and X-ray photoelectron spectroscopy. The results indicate that the three elements of B, C, N are chemically bonded with each other and atomic-level hybrids have been formed in the films. The boron carbon nitride films prepared in the present experiment possess a disordered structure. The influence of PN₂/PN₂+Ar, total pressure and substrate bias voltage on the composition of boron carbon nitride films is investigated. The atomic fraction of C atoms increases and the fractions of B, N decrease with the decrease of PN₂/PN₂+Ar from 75% to 0%. There is an optimum total pressure. That is to say, the atomic fractions of B, N reach a maximum and the fraction of C atoms reaches a minimum at the total pressure of 1.3 Pa. The boron carbon nitride films exhibit lower C content and higher B, N contents at lower bias voltages. And the boron carbon nitride films show higher C content and lower B, N contents at higher bias voltages.     

Study on the orientation of silver films by ion-beam assisted deposition

Low energy ion beam assisted deposition (IBAD) was employed to prepare Ag films on Mo/Si (100) substrate. It was found that Ag films deposited by sputtering method without ion beam bombardment were preferred (111) orientation. When the depositing film was simultaneously bombardment by Ar⁺ beam perpendicular to the film surface at ion/atom arrival ratio of 0.18, the prepared films exhibited weak (111) and (200) mixed orientations. When the direction of Ar⁺ beam was off-normal direction of the film surface, Ag films showed highly preferred (111) orientation. Monte Carlo method was used to calculate the sputtering yields of Ar⁺ ions at various incident and azimuth angles. The effects of channeling and surface free energy on the crystallographic orientation of Ag films were discussed.     

Electrodeposition and characterization of Cu/Co multilayers: Effect of individual Co and Cu layers on GMR magnitude and behavior

The present work discusses the successful electrodeposition of Cu/Co multilayers, exhibiting appreciable GMR of 12-14% at room temperature. The effect of individual Cu and Co layers on the magnitude and behavior of GMR has been studied. By varying the thickness of individual layers the field at which saturation in GMR is observed can be controlled. It was observed that for lower thicknesses of Co layer, the saturation fields are reduced below 1 kOe. The Cu layer thickness seems to control the nature of magnetic coupling and the saturation field, with the two showing a correlation.     

Optical, structural and fluorescence properties of nanocrystalline cubic or monoclinic Eu:Lu2O3 films prepared by pulsed laser deposition

Eu³⁺-doped lutetium oxide (Eu:Lu₂O₃) nanocrystalline films were grown on fused-silica substrates by pulsed laser deposition. Depending on deposition conditions (oxygen pressure, temperature and laser energy), the structure of the films changed from amorphous to crystalline and the cubic or monoclinic phases were obtained with varying preferential orientation and crystallite size. The monoclinic phase could be prepared for the first time at temperatures as low as 240 °C and in a narrow range of parameters. Although this phase has been previously reported for powder samples, it occurs only for high pressures and high temperatures preparation conditions. The refractive indices were measured by m-lines spectroscopy for both crystalline phases and their dispersion curve fitted by the Sellmeier expression. The specific Eu³⁺ fluorescence properties of the different phases, monoclinic and cubic, were registered and show modifications due to the disorder induced by the nanometric size of the crystallites, emphasised in particular by quasi-selective excitation in the charge transfer band.