Perpendicular magnetic anisotropy and magnetic proximity effect in Pt1−δFeδ/Co multilayer films

The perpendicular magnetic anisotropy (PMA) and magnetization in Pt_1−δFe_δ/Co (δ=0, 0.017, 0.04 and 0.06) multilayer films have been investigated. It is found that, on adding a small amount of Fe into the Pt layers, Pt/Co multilayer films maintain well-defined PMA at both 5 and 300 K along with significantly enhanced magnetization even at room temperature, which is far greater than the Curie temperature of Pt_1−δFe_δ dilute alloys. Further study demonstrates that the large enhancement of the magnetization in the Fe doped Pt/Co multilayers at 300 K arises from the bulk moment of the Pt_1−δFe_δ layers at the interface region, where the ferromagnetic order persists up to room temperature due to the strengthened exchange interactions between Fe atoms via strongly polarized Pt near the Pt_1−δFe_δ/Co interfaces. For the Pt_0.96Fe_0.04/Pt multilayers, the magnetically ordered region in each Pt_0.96Fe_0.04 layer extends over at least 10 Å from the interface at room temperature.     

Influence of Si-N interlayer on the microstructure and magnetic properties of γ′-Fe4N films

The (γ′-Fe₄N/Si-N)_n (n: number of layers) multilayer films and γ′-Fe₄N single layer film synthesized on Si (1 0 0) substrates by direct current magnetron sputtering were annealed at different temperatures. The structures and magnetic properties of as-deposited films and films annealed at different temperatures were characterized using X-ray diffraction, scanning electron microscopy and vibrating sample magnetometer. The results showed that the insertion of Si-N layer had a significant influence on the structures and magnetic properties of γ′-Fe₄N film. Without the addition of Si-N lamination, the iron nitride γ′-Fe₄N tended to transform to α-Fe when annealed at the temperatures over 300 °C. However, the phase transition from γ′-Fe₄N to ?-Fe₃N occurred at annealing temperature of 300 °C for the multilayer films. Furthermore, with increasing annealing temperature up to 400 °C or above, ?-Fe₃N transformed back into γ′-Fe₄N. The magnetic investigations indicated that coercivity of magnetic phase γ′-Fe₄N for as-deposited films decreased from 152 Oe (for single layer) to 57.23 Oe with increasing n up to 30. For the annealed multilayer films, the coercivity values decreased with increasing annealing temperature, except that the film annealed at 300 °C due to the appearance of phase ?-Fe₃N.     

Structural and magnetic properties of RF sputtered FePt/Fe multilayers

Series of [FePt(4min)/Fe(t_Fe)]₁₀ multilayers have been prepared by RF magnetron sputtering and post-annealing in order to optimize their magnetic properties by structural designs. The structure, surface morphology, composition and magnetic properties of the deposited films have been characterized by X-ray diffractometer (XRD), Rutherford backscattering (RBS), scanning electron microscope (SEM), energy dispersive X-ray spectroscope (EDX) and vibrating sample magnetometer (VSM). It is found that after annealing at temperatures above 500 °C, FePt phase undergoes a phase transition from disordered FCC to ordered FCT structure, and becomes a hard magnetic phase. X-ray diffraction studies on the series of [FePt/Fe]_n multilayer with varying Fe layer thickness annealed at 500 and 600 °C show that lattice constants change with Fe layer thickness and annealing temperature. Both lattice constants a and c are smaller than those of standard ones, and lattice constant a decreases as Fe layer deposition time increases. Only a slight increase in grain size was observed as Fe layer decreased in samples annealed at 500 °C. However, the increase in grain size is large in samples annealed at 600 °C. The coercivities of [FePt/Fe]_n multilayers decrease with Fe layer deposition time, and the energy product (BH)_max reaches a maximum in the samples with Fe layer deposition time of 3 min. Comparison of magnetic properties with structure showed an almost linear relationship between the lattice constant a and the coercivities of the FePt phase.     

The effects of Si3N4 interlayer on the thermal stability and hardness of Ti/TiNx (x = 0.5-1) nanolayered coatings

The polycrystalline Ti/TiN_x multilayer films were deposited by magnetron sputtering, and the as-deposited multilayer coatings were annealed at 500-800 °C for 2-4 h in vacuum. We investigated the effects of annealing temperature and annealing time on the microstructural, interfacial, and mechanical properties of the polycrystalline Ti/TiN_x multilayer films. It was found that the hardness increased with annealing temperature. This hardness enhancement was probably caused by the preferred crystalline orientation TiN(1 1 1). The X-ray reflectivity measurements showed that the layer structure of the coatings could be maintained after annealing at 500 °C and the addition of the Si₃N₄ interlayer to Ti/TiN_x multilayer could improve the thermal stability to 800 °C.     

Crystallization and electrochemical performance of La0.6Sr0.4Co0.2Fe0.8O3 − δ-Ce0.8Gd0.2O1.9 thin film cathodes processed by single solution spray pyrolysis

La_0.6Sr_0.4Co_0.2Fe_0.8O_3 − δ-Ce_0.8Gd_0.2O_1.9 (LSCF-CGO) thin films obtained by spray pyrolysis of a single precursor solution were investigated by XRD, TEM and impedance spectroscopy at annealing temperatures ranging from 500 to 900 °C. Films annealed at 600 °C contained a mixture of amorphous regions and crystalline regions composed of fine crystallites (< 5 nm). Annealing above 600 °C increased the ratio of crystalline to amorphous material, led to the segregation of the films into distinct LSCF and CGO phases, and promoted grain growth. The electrical behavior of the films depended on annealing temperature. At testing temperatures of 400 °C and below, the polarization resistance of films with lower annealing temperatures was larger than the polarization resistance of films with higher annealing temperatures. However, at testing temperatures of 500 °C and above the polarization resistance of films with lower annealing temperatures was equal to or lower than the polarization resistance of films with higher annealing temperatures. This was reflected by the activation energy that decreased with increasing annealing temperature. The varying electrical behavior may be related to microstructural changes that caused bulk diffusion to be the rate-limiting step in films with lower annealing temperatures and oxygen dissociation to be the rate-limiting step in films with higher annealing temperatures.     

A study of the effect of ZrO2 on the magnetic properties of FePt/ZrO2 multilayer

Fe_xPt_100−x(30 nm) and [Fe_xPt_100−x(3 nm)/ZrO₂]₁₀ (x = 37, 48, 57, 63, 69) films with different ZrO₂ content were prepared by RF magnetron sputtering technique, then were annealed at 550 °C for 30 min. This work investigates the effect of ZrO₂ doping on the microstructural evolution, magnetic properties, grain size, as well as the ordering kinetics of FePt alloy films. The as-deposited films behaved a disordered state, and the ordered L1₀ structure was obtained by post-annealing. The magnetic properties of the films are changed from soft magnetism to hard magnetism after annealing. The variation of the largest coercivities of [Fe_xPt_100−x/ZrO₂]₁₀ films with the Fe atomic percentage, x and differing amounts of ZrO₂ content reveals that as we increase the ZrO₂ content we must correspondingly increase the amount of Fe. This phenomenon suggests that the Zr or O atoms of ZrO₂ preferentially react with the Fe atoms of FePt alloy to form compounds. In addition, introducing the nonmagnetic ZrO₂ can reduce the intergrain exchange interactions of the FePt/ZrO₂ films, and the interactions are decreased as the ZrO₂ content increases, the dipole interactions are observed in FePt/ZrO₂ films as the ZrO₂ content is more than 15%.     

Growth, structural and optical transport properties of nanocrystal Zn1−xCdS thin films deposited by solution growth technique (SGT) for photosensor applications

Solution Growth Technique (SGT) has been used for deposition of Zn_1−xCdS nanocrystalline thin films. Various parameters such as solution pH (10.4), deposition time, concentration of ions, composition and deposition and annealing temperatures have been optimized for the development of device grade thin film. In order to achieve uniformity and adhesiveness of thin film on glass substrate, 5 ml triethanolamine (TEA) have been added in deposition solution. The as-deposited films have been annealed in Rapid Thermal Annealing (RTA) system at various temperature ranges from 100 to 500 °C in air. The changes in structural formation and optical transport phenomena have been studied with annealing temperatures and composition value (x). As-deposited films have two phases of ZnS and CdS, which were confirmed by X-ray diffraction studies; further the X-ray analysis of annealed (380 °C) films indicates that the films have nanocrystalline size (150 nm) and crystal structure depends on the films stoichiometry and annealing temperatures. The Zn_0.4CdS films annealed at 380 °C in air for 5 min have hexagonal structure where as films annealed at 500 °C have represented the oxide phase with hexagonal structure. Optical properties of the films were studied in the wavelength range 350-1000 nm. The optical band gap (E_g=2.94-2.30 eV) decreases with the composition (x) value. The effect of air rapid annealing on the photoresponse has also been observed on Zn_1−xCdS nanocrystal thin films. The Zn_1−xCdS thin film has higher photosensitivity at higher annealing temperatures (380-500 °C), and films also have mixed Zn_1−xCdS/Zn_1−xCdSO phase with larger grain size than the as-deposited and films annealed up to 380 °C. The present results are well agreed with the results of other studies.     

Magnetic properties of field-annealed FeCo thin films

Fe₅₀Co₅₀ thin films with thickness of 30 and 4 nm have been produced by rf sputtering on glass substrates, and their surface has been observed with atomic force microscopy (AFM) and magnetic force microscopy (MFM); MFM images reveal a non-null component of the magnetization perpendicular to the film plane. Selected samples have been annealed in vacuum at temperatures of 300 and 350 °C for times between 20 and 120 min, under a static magnetic field of 100 Oe. DC hysteresis loops have been measured with an alternating gradient force magnetometer (AGFM) along the direction of the field applied during annealing and orthogonally to it. Samples with a thickness of 4 nm display lower coercive fields with respect to the 30 nm thick ones. Longer annealing times affect the development of a harder magnetic phase more oriented off the film plane. The field applied during annealing induces a moderate magnetic anisotropy only on 30 nm thick films.     

Thermal annealing of FePt thin films by millisecond plasma arc pulses

A series of 20 and 100 nm Fe₅₃Pt₄₇ thin films sputter-deposited onto Si substrates have been thermally annealed using a pulsed thermal plasma arc lamp. A series of one, three or five pulses were applied to the thin films with widths of either 50 or 100 ms. The microstructure and magnetic properties of these annealed Fe₅₃Pt₄₇ films are discussed according to the various annealing conditions and A1 to L1₀ phase transformation. Upon pulse annealing, the average in-plane grain size of 15 nm (nearly equivalent for both film thicknesses) was observed to increase to values near 20 nm. In general, increasing the pulse width or number of pulses increased the L1₀ order parameter, tetragonality of the c/a ratio and coercivity of the specimen. The exception to this trend was for five pulses at 100 ms for both film thicknesses, which indicated a reduction of the order parameter and coercivity. This reduction is believed to be a result of the interdiffusion of Fe and Pt into the Si substrate and the formation of iron oxide clusters in the grain boundaries characterized by atom probe tomography.     

Thermo-stimulated surface segregation in the ordering alloy Pt80Co20(1 1 1): Experiment and modeling

In this paper, a method of Ionization Spectroscopy (IS) is proposed for the non-destructive layer-by-layer analysis of the elemental composition of a solid surface. Using ionization energy loss spectra, a layer-by-layer concentration profile of the Pt₈₀Co₂₀(1 1 1) alloy surface is obtained for different annealing temperatures. For the disordered Pt₈₀Co₂₀(1 1 1) at room temperature, the first atomic layer consists of pure Pt with damped oscillations in the deeper layers. Heating the sample reduces the oscillations. However, at a temperature of 823 K, a sandwich-like structure of the type Pt/Co/Pt was found in the first three atomic layers. For the ordered state the first atomic layer also consists of pure Pt with bulk concentration in other layers. LEED analysis shows a p(2 × 2) superstructure for the surface of the ordered Pt₈₀Co₂₀(1 1 1) alloy. The segregation behavior in this alloy is further studied by Monte Carlo (MC) simulations combined with the Constant Bond Energy (CBE) model. The results of the MC simulations agree well with the experiments at the higher temperatures, both for the surface composition and the concentration depth profile. At lower temperatures, some discrepancies exist between the MC results and the measured concentration profile.     

Low-temperature ordering and enhanced coercivity of L10-FePt thin films with Al underlayer

FePt multilayer films with and without Al underlayer were prepared by magnetron sputtering on SiO₂ substrate and subsequently annealed in vacuum. Experimental results suggest that the existence of Al underlayer can effectively reduce the ordering temperature and increase the coercivity of FePt films. Due to the slight larger lattice constant of Al underlayer than that of FePt films, [Fe (0.66 nm)/Pt (0.84 nm)]₃₀ films begin to order at 350 °C and the coercivity of them reach to 5.7 kOe after annealing at 400 °C for half an hour.     

Correlation between microstructure and optical properties of nano-crystalline TiO2 thin films prepared by sol-gel dip coating

Titanium dioxide thin films have been prepared from tetrabutyl-orthotitanate solution and methanol as a solvent by sol-gel dip coating technique. TiO₂ thin films prepared using a sol-gel process have been analyzed for different annealing temperatures. Structural properties in terms of crystal structure were investigated by Raman spectroscopy. The surface morphology and composition of the films were investigated by atomic force microscopy (AFM). The optical transmittance and reflectance spectra of TiO₂ thin films deposited on silicon substrate were also determined. Spectroscopic ellipsometry study was used to determine the annealing temperature effect on the optical properties and the optical gap of the TiO₂ thin films. The results show that the TiO₂ thin films crystallize in anatase phase between 400 and 800 °C, and into the anatase-rutile phase at 1000 °C, and further into the rutile phase at 1200 °C. We have found that the films consist of titanium dioxide nano-crystals. The AFM surface morphology results indicate that the particle size increases from 5 to 41 nm by increasing the annealing temperature. The TiO₂ thin films have high transparency in the visible range. For annealing temperatures between 1000 and 1400 °C, the transmittance of the films was reduced significantly in the wavelength range of 300-800 nm due to the change of crystallite phase and composition in the films. We have demonstrated as well the decrease of the optical band gap with the increase of the annealing temperature.     

Effect of nanoscale thin films of Dy2Fe14B on the magnetic hysteresis characteristics of melt-spun ribbons of Nd2Fe14B

The effectiveness of nanoscale Dy₂Fe₁₄B thin films on coercivity and energy product of melt-spun ribbons of Nd₂Fe₁₄B at high temperatures was investigated. It is hypothesized that the nanoscale Dy-thin film will act as an obstacle for the nucleation of reverse domains and also maximize the energy of domain walls and thereby improve the magnetic performance at high temperatures. Pulsed laser deposition (PLD) of amorphous Dy₂Fe₁₄B layers on Nd₂Fe₁₄B melt-spun ribbons was performed for a nominal thickness of 40 nm. The coated ribbons were then annealed in environmentally controlled quartz furnace at two different cycles (750 °C for 15 min and 900 °C for 2 h) to cause crystallization. Magnetic hysteresis tests conducted at 300 and 400 K revealed that there is small but consistent improvement in the magnetic properties of the coated ribbons annealed at 750 °C for 15 min. However, higher temperature annealing (900 °C for 2 h) drastically reduced the magnetic properties. The incomplete recrystallization of amorphous structure at 750 °C for 15 min and large grain growth and formation of non-magnetic phases at 900 °C for 2 h are believed to be responsible for not meeting the expected magnetic performance.     

Structure and magnetic properties of magnetron-sputtered [(Fe/Pt/Fe)/Au]n multilayer films

Using dc magnetron sputtering, Fe/Pt/Au multilayer films were prepared, and the effects of Au layer thickness and annealing temperature on structure and magnetic properties of the Fe/Pt/Au multilayer films were investigated. The as-deposited Fe/Pt/Au multilayer films have good periodic structure with composition modulation along the growth direction. The stress stored in the as-deposited films promoted the ordering of the films annealed at 400 °C. When the films were annealed at 500 °C, the thicker Au layer could restrain the order-disorder transformation region volume and lead to the decrease of the ordered volume fraction with Au layer thickness increasing.     

The impact of annealing temperature and time on the electrical performance of Ti/Pt thin films

In this study, we focus on the influence of annealing time t_PDA (i.e. 30 min and 630 min) on the room-temperature resistivity of electron-beam-evaporated titanium/platinum thin films when exposed to thermal loads up to temperatures T_PDA of 700 °C. The titanium has a fixed thickness of 5 nm and serves as an adhesion layer. The thickness d_f,Pt of the platinum top layer is varied between 21 and 97 nm. Up to annealing temperatures of 450 °C, the film resistivity of the bi-layer system is linearly correlated with the reciprocal platinum film thickness independent of t_PDA, as expected from the size effect. At t_PDA = 30 min, the change in intrinsic film stress dominates the electrical behavior in this annealing regime, predominantly at large d_f,Pt values. Compared to t_PDA = 630 min, however, the increase in resistivity especially at low platinum film thickness is substantially larger demonstrating that titanium starts to diffuse at these long annealing times even at moderate temperatures. At T_PDA = 600 °C, the diffusion of titanium into the top layer leads to an enhanced increase in film resistivity ρ_f, especially at low platinum thicknesses and low annealing times, as the mean penetration depth of diffused titanium is under these conditions in order of d_f,Pt. Above T_PDA = 600 °C, ρ_f is slightly increased at t_PDA = 30 min. At t_PDA = 630 min, however, the film resistivity is decreased at d_f,Pt < 58 nm. This is attributed to grain growth and re-crystallization effects. Furthermore, the mean penetration depths of titanium substantially exceed d_f,Pt resulting predominantly in Ti_xO_y formation on the top film surface and hence, having low impact on ρ_f.     

Solid phase epitaxy of Ge films on CaF2/Si(1 1 1)

At room temperature deposited Ge films (thickness < 3 nm) homogeneously wet CaF₂/Si(1 1 1). The films are crystalline but exhibit granular structure. The grain size decreases with increasing film thickness. The quality of the homogeneous films is improved by annealing up to 200 °C. Ge films break up into islands if higher annealing temperatures are used as demonstrated combining spot profile analysis low energy electron diffraction (SPA-LEED) with auger electron spectroscopy (AES). Annealing up to 600 °C reduces the lateral size of the Ge islands while the surface fraction covered by Ge islands is constant. The CaF₂ film is decomposed if higher annealing temperatures are used. This effect is probably due to the formation of GeF_x complexes which desorb at these temperatures.     

Early-stage ordering in in-situ annealed Fe51Pt49 films

We evidenced an early-stage ordering (ESO) in Fe₅₁Pt₄₉ film before the appearance of superlattice diffraction (long-range-order, LRO) using 40-nm-thick films prepared by magnetron sputtering onto quartz substrate. The appearance of L1₀ phase for samples deposited at substrate temperatures (T_s) 400 °C and higher was verified by X-ray diffraction. Surface roughness of Fe₅₁Pt₄₉ films, obtained via X-ray specular reflectivity with computational fitting, increases from 3.8 to 11 Å as T_s is increased from 25 to 275 °C. As further increase of T_s to 375 °C, the roughness drops to 3.2 Å and then increases again to 38 Å with T_s up to 700 °C. Measurement on residual strain demonstrates that it is initially compressive at T_s<400 °C. Thereafter the strain transfers to a tensile one and increases in magnitude as increasing T_s up to 700 °C corresponding to LRO transformation. Local atomic rearrangement is observed for samples deposited at T_s>250 °C by using extended X-ray absorption fine structure. Coercivity of films increases from 10 to 460 Oe as T_s increase from 25 to 375 °C (ESO) and then from 460 to 10,700 Oe with T_s 375-700 °C (normal LRO). The worked out quantitative estimation of ESO engages with that of LRO before T_s 400 °C.     

Effect of thermal annealing on the structure and magnetism of Fe-doped ZnO nanocrystals synthesized by solid state reaction

High purity Fe₂O₃/ZnO nanocomposites were annealed in air at different temperatures between 100 and 1200 °C to get Fe-doped ZnO nanocrystals. The structure and grain size of the Fe₂O₃/ZnO nanocomposites were investigated by X-ray diffraction 2θ scans. Annealing induces an increase of the grain size from 25 to 195 nm and appearance of franklinite phase of ZnFe₂O₄. Positron annihilation measurements reveal large number of vacancy defects in the interface region of the Fe₂O₃/ZnO nanocomposites, and they are gradually recovered with increasing annealing temperature. After annealing at temperatures higher than 1000 °C, the number of vacancies decreases to the lower detection limit of positrons. Room temperature ferromagnetism can be observed in Fe-doped ZnO nanocrystals using physical properties measurement system. The ferromagnetism remains after annealing up to 1000 °C, suggesting that it is not related with the interfacial defects.     

Influence of heat treatment on the structure and magnetic properties of the Co/Zr and Co/Hf multilayer amorphous films

The influence of annealing on the structure and magnetic properties of amorphous Co/Zr and Co/Hf multilayer films was studied with particular attention to the dependence of the magnetic properties, thermal stability and crystallization process on layer composition and thickness. The temperature at which crystallization commences increases from 400 to 460 °C as the layer thickness d_Zr or d_Hf increases from 6 to 18 Å, and decreases from 450 to 400 °C as d_Co increases from 12 to 18 Å. Multilayers containing 19–60 at% Zr were studied. The specific magnetization was found to increase even below the temperature at which crystallization commences. Our data are compared with non-multilayer Co–Zr amorphous films and rapidly quenched metallic glasses.     

Thermal behavior and catalytic activity in naphthalene destruction of Ce-, Zr- and Mn-containing oxide layers on titanium

The present paper is devoted to studies of the composition and surface structure, including those after annealing at high temperatures, and catalytic activity in the reaction of naphthalene destruction of Ce-, Zr- and Mn-containing oxide layers on titanium obtained by means of the plasma electrolytic oxidation (PEO) method. The composition and structure of the obtained systems were investigated using the methods of X-ray phase and energy dispersive analysis and scanning electron microscopy (SEM). It was demonstrated that Ce- and Zr- containing structures had relatively high thermal stability: their element and phase compositions and surface structure underwent virtually no changes after annealing in the temperature range 600-800 °C. Annealing of Ce- and Zr-containing coatings in the temperature range 850-900 °C resulted in substantial changes of their surface composition and structure: a relatively homogeneous and porous surface becomes coated by large pole-like crystals. The catalytic studies showed rather high activity of Ce- and Zr-containing coatings in the reaction of naphthalene destruction at temperatures up to 850 °C. Mn-containing structures of the type MnO_x + SiO₂ + TiO₂/Ti have a well-developed surface coated by “nano-whiskers”. The phase composition and surface structure of manganese-containing layers changes dramatically in the course of thermal treatment. After annealing above 600 °C nano-whiskers vanish with formation of molten structures on the surface. The Mn-containing oxide systems demonstrated lower conversion degrees than the Ce- and Zr-containing coatings, which can be attributed to substantial surface modification and formation of molten manganese silicates at high temperatures.