Structure, magnetic and magnetostrictive properties of as-deposited Fe-Ga thin films

Polycrystalline Fe_100−xGa_x (19?x?23) films were grown on Si(1 0 0) substrates at different partial pressures of sputtering gas ranging from 3 to 7 μbar. Microstructural, magnetic and magnetostrictive properties were studied using X-ray diffraction (XRD), atomic force microscopy (AFM), energy dispersive spectroscopy (EDS) and magneto-optic Kerr effect (MOKE) magnetometry respectively. X-ray diffraction showed that all films have the body-centered cubic (bcc) Fe-Ga phase with the 〈1 1 0〉 direction out of the film plane. Magnetic characterization of the films showed that the films prepared at 3 μbar had weak uniaxial anisotropy whereas films grown at Ar pressures in the range 4-7 μbar were magnetically isotropic. The effective saturation magnetostriction constants (λ_eff) of the films were measured using the Villari effect. It was found that effective saturation magnetostriction constants were almost constant over the Ga composition range achieved by varying the sputtering pressure. The measured effective magnetostriction constants fit closely to the calculated saturation magnetostriction constants of 〈1 1 0〉 textured polycrystalline films with the 〈1 1 0〉 directions slightly canted with respect to the normal to the sample surface. It was found that a high pressure of the sputtering gas effected the magnetic softness of the films. The saturation field increased and remanence ratio decreased with increase in pressure.     

Investigation of hard magnetic properties in the Fe-Pt system by combinatorial deposition of thin film multilayer libraries

The magnetic properties of annealed Fe-Pt multilayer thin films with a broad composition range were investigated in order to identify the effects of composition and annealing temperature on the achievable coercive field, and to identify its maximum at low processing temperatures. Two types of multilayer systems were deposited as materials libraries to vary the composition from Fe₂₀Pt₈₀ to Fe₇₅Pt₂₅. The first type of multilayer was comprised of alternating opposing wedges, whereas the second type consisted of repeated uniform Fe and Pt layers interspersed periodically with Fe wedge layers. It was found that coercive fields μ₀H_C > 0.7 T can be achieved at an annealing temperature of about 300 °C (60 min) for both types of multilayers as long as the composition is close to 50:50. Higher annealing temperatures are needed for films, which deviate from this composition. Increasing the annealing temperature up to 700 °C leads to increased coercivity values. Multilayers with additional Fe layers showed increased remanence but reduced coercive fields.     

MOCVD growth, structure and magnetic properties of Fe films grown on GaAs (001) substrates

Thin iron films have been grown on (001) GaAs substrates by low pressure metal organic chemical vapor deposition (LP-MOCVD) at different temperatures with the pressure of 150 Torr. X-ray diffraction (XRD) analysis showed that all films have only one strong diffraction peak (110). The surface of Fe film became smooth with increasing the growth temperature. Magnetization measurements showed that the Fe films grown at different temperatures were ferromagnetic with easy axis parallel to the film surface and hard axis perpendicular to the substrates. The field dependence of magnetization along two axes showed a remarkable difference, implying that the samples have strong magnetic anisotropy. Furthermore, when the applied magnetic field is perpendicular to the Fe surface, a sharp jump in the hysteresis loop could be observed, followed by a broad shoulder, which is related to the interface effect, the existence of carbon and the formation of 180^°/90^° magnetic domains.     

Structure and RT ferromagnetism of Fe-doped AlN films

Al_1−xFe_xN_1−δ thin films with 0 ≤ x ≤ 13.6% were deposited by dc magnetron co-sputtering at room temperature (RT). It is found that Fe atom will substitutes the Al atom in the lattice when x ≤ 1.2%, while it will embed into the interstice of the lattice at larger Fe content. RT ferromagnetism was observed in all doped samples. A maximum saturated magnetization 2.81 emu/cm³ of the film is found to be induced by AlFeN ternary alloy when x = 1.2%.     

Effects of Mn flux on ferromagnetic properties of (Ga,Mn)N films grown by PEMBE

Effects of Mn flux on the magnetic properties of (Ga,Mn)N films grown on sapphire substrate by plasma-enhanced molecular beam epitaxy (PEMBE) discussed. The (Ga,Mn)N thin films were found to exhibit ferromagnetic ordering at room temperature without any secondary phases by X-ray diffraction and alternating gradient magnetometer. It is found that, although the surface morphology and the electrical properties are degraded with increasing Mn concentration, the magnetic properties of the films improve.     

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.     

Nd composition dependence of microstructure and magnetic properties for gradient sputtered NdFeB films

NdFeB films with Nd compositions varied from 13.34 to 24.30 at% were deposited by DC gradient sputtering using targets Nd_12.5Fe_71.5B₁₆ and Nd. The hard magnetic properties, grain growth direction and magnetic domain structures were dramatically influenced by Nd composition. The samples with intermediate Nd concentrations exhibited optimal magnetic properties and microstructures, such as large squareness ratio over 0.9, large energy product up to 174 kJ/m³, and vertical domain structure. However, the samples with higher and lower Nd compositions showed almost isotropic loops. (0 0 l) as main X-ray diffraction peaks in the optimal Nd composition region indicated most of Nd₂Fe₁₄B grains with c-axis perpendicular to the film plane, while NdFeB grains in other region are almost random growth. The good magnetic properties can be attributed to the vertical growth of Nd₂Fe₁₄B grains.     

Thickness dependence of the magnetic properties and magnetoimpedance effect in CoFeAlO thin films

The change of the magnetic properties and magnetoimpedance effect of Co–Fe–Al–O thin films with film thicknesses 50–1200 nm has been investigated. The coercivity and the anisotropy field changed strongly with increase of film thickness, while the saturation induction almost remained unchanged. The maximum value of GMI effect obtained about 33% for a film thickness of 1200 nm.     

Influence of direct current plasma magnetron sputtering parameters on the material characteristics of polycrystalline copper films

Physical vapor processes using glow plasma discharge are widely employed in microelectronic industry. In particular magnetron sputtering is a major technique employed for the coating of thin films. This paper addresses the influence of direct current (DC) plasma magnetron sputtering parameters on the material characteristics of polycrystalline copper (Cu) thin films coated on silicon substrates. The influence of the sputtering parameters including DC plasma power and argon working gas pressure on the electrical and structural properties of the thin Cu films was investigated by means of surface profilometer, four-point probe and atomic force microscopy.     

Fabrication and characterization of facing-target reactive sputtered polycrystalline TiO2 films

Polycrystalline TiO₂ films were fabricated using dc facing-target reactive sputtering at different sputtering pressures. The films deposited consist of pure anatase phase or a mixture of anatase and rutile and increasing rutile content to some extent deteriorates the crystallinity of the anatase. It was found that the plasma heating effect, which plays the role of substrate heating, is an important factor for the crystallinity of the films in the case of without substrate heating. The roughness of the films increases monotonically with the increase of the sputtering pressure, which can be ascribed to the decrease in the mobility of the impinging particles. UV-vis transmission measurements reveal that the pure anatase films have higher transmittance than those having mixed phases of anatase and rutile. The band gap value decreases from ∼3.35 to 3.29 eV owing to the increase in the fraction of rutile phase.     

Microwave and static magnetic properties of multi-layered iron-based films

Thin ferromagnetic films with in-plane magnetic anisotropy are promising materials for obtaining high microwave permeability. To produce a bulk massive sample from thin films, multi-layer films made of a number of many thin films may be used. The paper reports on an experimental study of microwave and static magnetic properties of multi-layer iron-based films and composite samples made of these. The multi-layer films under study are deposited onto a mylar substrate by a magnetron-sputtering process performed in Ar atmosphere with controlled N₂ admixture. The sputtered iron layers are alternated with SiO₂ layers. The measured static and microwave magnetic properties of the bulk sample are found to differ from the properties of constituent films. This is an evidence for strong interactions between the magnetic layers in the sample, which interact at distances exceeding greatly the distance between adjacent magnetic layers. A theoretic model is developed to account for magneto-dipole interactions between iron films in a multi-layer system. The model explains the anomalously high demagnetization field of the sample observed in the measurements.     

Optical and magnetic properties of laser-deposited Co-doped ZnO thin films

We report the optical and magnetic properties of laser-deposited Zn_1−xCo_xO (x=0.06-0.3) thin films with no intentional electrical carrier doping. The analysis of the high-temperature magnetization data provides an unambiguous evidence that antiferromagnetic superexchange interaction is the dominant mechanism of the exchange coupling between Co ions in Zn_1−xCo_xO alloy, yielding the value of the effective exchange integral J₁/k_B to be about −27 K. The low-temperature magnetization data reveals a spin glass transition in Zn_1−xCo_xO alloy for the Co content x>0.15, giving the value of the spin freezing temperature T_f to be ∼8 and ∼12 K for x=0.2 and 0.25, respectively. Optical spectra analysis shows a linear increase of the band gap E_g with the increase of the Co content following E_g=3.231+1.144x eV.     

The influence of substrate on the properties of Er2O3 films grown by magnetron sputtering

The structural properties and the room temperature luminescence of Er₂O₃ thin films deposited by RF magnetron sputtering have been studied. Films characterized by good morphological properties have been obtained by using a SiO₂ interlayer between the film and the Si substrate. The evolution of the properties of the Er₂O₃ films due to rapid thermal annealing processes in O₂ ambient performed at temperatures in the range 800-1200 °C has been investigated in details. The existence of well-defined annealing conditions (temperature of 1100 °C or higher) allowing to avoid the occurrence of extensive chemical reactions with the oxidized substrate has been demonstrated and an increase of the photoluminescence (PL) intensity by about a factor of 40 with respect to the as deposited material has been observed. The enhanced efficiency of the photon emission process has been correlated with the longer lifetime of the PL signal. The same annealing processes are less effective when Er₂O₃ is deposited on Si. In this latter case interfacial reactions and pit formation occur, leading to a material characterized by stronger non-radiative phenomena that limit the PL efficiency.     

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.     

Effect of Co underlayer on soft magnetic properties and microstructure of FeCo thin films

High saturation magnetization soft magnetic FeCo (=Fe₆₅Co₃₅) films were prepared using a thin Co underlayer. The FeCo/Co films exhibited a well-defined in-plane uniaxial anisotropy with easy axis coercivity (H_ce) of 10 Oe and hard axis coercivity (H_ch) of 3 Oe, and a half reduction of H_c with H_ce=4.8 Oe and H_ch=1.0 Oe was obtained when the composition was adjusted to 25 at% Co. The effective permeability of the films remains flat around 250 to 800 MHz. The saturation magnetostriction was 5.2×10⁻⁵ and the intrinsic stress was 0.8 GPa in FeCo single layer, both were slightly reduced by Co underlayer. The Co underlayer changed the preferred orientation of the FeCo films from (2 0 0) to (1 1 0) but more significantly, reduced the average grain size from ∼74 to ∼8.2 nm. It also reduced the surface roughness from 2.351 to 0.751 nm. The initial stage and interface diffusion properties were examined by TEM and XPS.     

Structural and electrical properties of tantalum nitride thin films fabricated by using reactive radio-frequency magnetron sputtering

TaN thin film is an attractive interlayer as well as a diffusion barrier layer in [FeN/TaN]_n multilayers for the application as potential write-head materials in high-density magnetic recording. We synthesized two series of TaN films on glass and Si substrates by using reactive radio-frequency sputtering under 5-mtorr Ar/N₂ processing pressure with varied N₂ partial pressure, and carried out systematic characterization analyses of the films. We observed clear changes of phases in the films from metallic bcc Ta to a mixture of bcc Ta(N) and hexagonal Ta₂N, then sequentially to fcc TaN and a mixture of TaN with N-rich phases when the N₂ partial pressure increased from 0.0% to 30%. The changes were associated with changes in the grain shapes as well as in the preferred crystalline orientation of the films from bcc Ta [100] to [110], then to random and finally to fcc TaN [111], correspondingly. They were also associated with a change in film resistivity from metallic to semiconductor-like behavior in the range of 77–295 K. The films showed a typical polycrystalline textured structure with small, crystallized domains and irregular grain shapes. Clear preferred (111) stacks parallel to the substrate surface with embedded amorphous regions were observed in the film. TaN film with [111]-preferred orientation and a resistivity of 6.0 mΩ cm was obtained at 25% N₂ partial pressure, which may be suitable for the interlayer in [FeN/TaN]_n multilayers. Received: 6 December 1999 / Accepted: 24 July 2000 / Published online: 9 November 2000     

Playback performance and microstructure of sputtered tape media formed by facing targets sputtering

Sputtered tape media of a CoPtCr–SiO₂ magnetic layer with a Ru underlayer was fabricated on a thin Aramid film by a facing targets sputtering (FTS) system at room temperature with no cooling. Transition electron microscope (TEM) images show columnar epitaxial growth of hcp-CoPtCr(1 0 0) plane on hcp-Ru(1 0 0). Average grain diameter of 10.2 nm with dispersion of 20.2% was obtained from TEM images. Enrichment of Co and Pt inside grains and segregation of Cr and Si to boundary were confirmed by point energy dispersive spectroscopy (EDS) measurements. Playback performance test on sputtered sample indicated that SNR is higher and PW50 value is lower than that of commercial coated tapes. These good playback properties could come from fine and isolated grain structure of magnetic layer of sputtered sample, as observed by TEM.     

Investigation of microstructure evolution in Pt-doped TiO2 thin films deposited by rf magnetron sputtering

Pt-doped titanium dioxide or titania (TiO₂) films were grown by rf magnetron sputtering and then annealed in the conventional thermal annealing (CTA) process. Raman spectroscopy was used to characterize the structure of the films deposited. The effect of sputtering parameters was studied in focus of the nucleation sites energies (influenced by the substrate temperature) and substrate bombardment energies (influenced by the sputtering pressure or rf power). The X-ray diffractions technique was used to investigate the structural variation after the films were annealed at different temperatures. It was found that 0.75% Pt-doped TiO₂ film exhibits better thermal stability and smaller grain sizes than 0.35% Pt-doped TiO₂ film, suggesting that the suppression of crystallization can be expected with a proper increase of Pt doping level. And the obtained optical transparency higher than 80% even after annealing has demonstrated the films’ prospect for future developments.     

Influence of substrate temperature on the texture of barium ferrite film by magnetron sputtering

Barium ferrite thin films have been prepared by radio frequency magnetron sputtering on a sapphire (0 0 1) substrate at substrate temperature of 500 °C and 650 °C, respectively. The films were further annealed in air at 1000 °C for 5 h. X-ray diffraction shows that the films at the lower substrate temperatures have a good epitaxial relation with respect to the substrate, while the samples under the higher substrate temperatures have (1 0 9) planes parallel to the substrate. The remanence ratio decreases from 0.82 to 0.47 when the substrate temperature is increased. We attribute the variation of the growth direction to the enhanced vertical mobility of the deposited atoms when the substrate temperature is increased.     

Effects of the sputtering time of ZnO buffer layer on the quality of GaN thin films

ZnO thin films with different thickness (the sputtering time of ZnO buffer layers was 10 min, 15 min, 20 min, and 25 min, respectively) were first prepared on Si substrates using radio frequency magnetron sputtering system and then the samples were annealed at 900 °C in oxygen ambient. Subsequently, a GaN epilayer about 500 nm thick was deposited on ZnO buffer layer. The GaN/ZnO films were annealed in NH₃ ambient at 950 °C. X-ray diffraction (XRD), atom force microscopy (AFM), X-ray photoelectron spectroscopy (XPS) and photoluminescence (PL) were used to analyze the structure, morphology, composition and optical properties of GaN films. The results show that their properties are investigated particularly as a function of the sputtering time of ZnO layers. For the better growth of GaN films, the optimal sputtering time is 15 min.