X-ray and Magnetoresistance Measurements of Electrodeposited Cu-Co Granular Films

Granular CoxCu1-x alloy films were prepared by electrodeposition at room temperature directly onto semiconducting Si substrate. X-ray diffraction (XRD) revealed that the as-deposited films formed single phase metastable fcc alloy structure. The fcc lattice parameter αwas found to decrease linearly with increasing Co concentration x in the studied range. The giant magnetoresistance (GMR) of the films was improved after annealing. Pure Co fcc diffraction peaks were observed in the diffractogram of the annealed sample, indicating phase separation occurred upon annealing. The optimal annealing temperature was 450℃. The maximum of magnetoresistance (MR) ratio 8.21% was obtained for the Co20Cu80 thin film after annealing at 450℃for 1 h. The saturation field decreased upon annealing in the MR curves of Co20Cu80 film.     

Domains in CoCr investigated by neutron depolarization

Polarized neutrons (λ = 0.47 nm) are transmitted through RF and magnetron sputtered CoCr films (0.3-5 μm thick) with the polarization vector in the plane or perpendicular to the plane of the film. In the former case we can deduce from the depolarization the effective height heffof the domains and from the angular dependence of the depolarization the section width δ (which is proportional to the domain width) in the remanent states after perpendicular and after in-plane saturation. As expected, heffappears to be larger after perpendicular saturation and for a film thickness h ∼ 400 nm, heffapproaches h. This is attributed to the disappearance of reversed spike domains in the thinnest films. The lower hefffound in magnetron films with a lower surface/bulk coercivity ratio is also consistent with spike domain theory. The section width δ is found to he proportional to hx with x depending on the preparation or magnetic history of the film between 0.6 and 0.8. For magnetron films δ is ∼ 1.5 as large as in RF films of equal thickness, in qualitative agreement only with the fact that K1is twice as large as for RF films.     

Media and tip trajectory optimization for high-density MFM-based perpendicular recording

In this paper, we investigate the feasibility of using a magnetic force microscopy scheme for recording and retrieving magnetic marks for ultrahigh-density, ultralow power applications. We will address the main design considerations while designing such a system. Then, using the impulse-response and inverse-convolution technique, we deduce a novel tip trajectory for the optimum recording process. We will also apply extensive optimization for a Co/sub x/Cr/sub y/Pt/sub 1-x-y/ perpendicular media structure to maximize the signal-to-noise ratio (SNR). An areal density of up to 0.3 Tb/in/sup 2/ is shown to be achievable with thermally stable magnetic marks and a SNR of 20-25 dB in the existence of additional electronic noise.     

Dependence of GMR on NiFe layer thickness in high sensitive simple spin valve

The dependence of the giant magnetoresistance on Ni/sub 81/Fe/sub 19/ soft magnetic layer thickness is investigated experimentally for a simple spin valve with a top-pinned structure of Ta (6 nm)/Ni/sub 81/Fe/sub 19//Co/sub 90/Fe/sub 10/ (1 nm)/Cu (1.8 nm)/Co/sub 90/Fe/sub 10/ (3.5 nm)/Ir/sub 20/Mn/sub 80/ (8 nm)/Ta (6 nm). With Ni/sub 81/Fe/sub 19/ thickness increased from 6 nm to 7 nm, the magnetoresistance (MR) ratio decreases sharply from 8.34% to 3.34%, whereas it changes only slightly within the thickness ranges from 2-6 nm and from 7-12 nm, and larger MR ratios are obtained in the range from 2-6 nm. For a spin valve with an optimized thickness of Ir/sub 20/Mn/sub 80/ (11 nm) and top Ta (3 nm), the MR dependence is in accordance with the former structure when Ni/sub 81/Fe/sub 19/ thickness changes from 3.5 to 5.5 nm, and an optimized spin valve with 4.5-nm-thick Ni/sub 81/Fe/sub 19/ is obtained. This spin valve has a large MR ratio (9.15%), low coercive force (0.85 Oe), and high sensitivity, which makes it promising for applications.     

Effects of rare-earth element substitution on magnetostrictive properties of polycrystalline Tb-Dy-Fe alloys

Magnetostrictive properties of (Tb/sub 0.5/Dy/sub 0.5/)/sub 1-x/RE/sub x/Fe/sub 1.9/ (x=0-0.05, RE=Y, Ce, Sm, Gd, Ho, Yb) polycrystalline compounds were studied. Each rare-earth element formed a RE-Fe/sub 2/ Laves compound with a different lattice spacing. Corresponding to this difference, (Tb/sub 0.5/Dy/sub 0.5/)/sub 0.95/RE/sub 0.05/Fe/sub 1.9/ alloys showed a variation in lattice spacing as a result of the substitution of rare-earth elements and the prestress dependence of magnetostriction changed noticeably. In the case of Y, Sm, and Gd substitution, which showed greater lattice spacing than that of the Tb/sub 0.5/Dy/sub 0.5/Fe/sub 1.9/ alloy, the prestress dependence and maximum magnetostriction decreased. On the other hand, in the case of Ce, Ho, and Yb substitution, which showed a decrease in lattice spacing, the conspicuous prestress dependence was the same as that of the Tb/sub 0.5/Dy/sub 0.5/Fe/sub 1.9/ alloy and the maximum magnetostriction was greater than that of the latter alloy.     

(Fe,Co)-P thin films prepared with a reactive evaporation method

Magnetic properties of (Fe,Co)/sub 2/P thin films prepared with the thermal-activated reactive evaporation method were investigated for recording media application. Above 300 degrees C, metals (Fe,Co) and phosphorus react to form M/sub 2/P. The coercive forces of these films had a maximum value of 1.3 kOe at 10% Co concentration, and the saturation magnetization increased with the increase in Co concentration. Annealing at 500 degrees C for 30 min increased the coercive force of the films up to two times. The reproduced output from the isolated magnetization transitions of a (Fe,Co)-P-film rigid disk with a ring head showed waveforms of typical longitudinal recording. A recording density of 62 kfrpi at D/sub 50/ was attained with a disk medium of about an 800-AA-thick layer.<>     

NiCo films with perpendicular magnetization anisotropy deposited on dielectric substrate by using polyol process

In this paper, the polyol process, a catalyst free, non-aqueous, and electroless process, is developed to deposit the nanostructured Ni_xCo_100 ? x magnetic films on aluminum nitride (AlN) substrate. Nickel (II) acetate tetrahydrate and cobalt (II) acetate tetrahydrate were reduced by ethylene glycol (EG) at 180 °C, and the reduced Ni and Co nanostructures were deposited on the AlN substrate merged in boiling EG for 60 min. The elongated nanostructures in the films are detected through the scanning electron microscopy (SEM). Interestingly, some of the elongated nanostructures are pointing out of the substrate. It indicates that the component ratio of Ni and Co in the films is different with the starting precursor molar ratio. The film thickness increases from 1 to 1.8 μm when the atomic ratio of Co (at.%) in the film increased from 44.6% to 70.8%. Furthermore, it is found that the crystallite size decreases from 44 to 25 nm with increasing Ni (at.%). In addition, the magnetic properties have been analyzed through vibrating sample magnetometer (VSM) at room temperature. The results show that the films have the perpendicular preferred anisotropy. The anisotropy field (H_K) for the Ni₅₀Co₅₀ is about 4.75 kOe, which is possibly caused by the assembled direction of the elongated nanostructures.     

Sputtered FeCoN soft magnetic thin films with high resistivity

Fe/sub 70/Co/sub 30/N thin films with thickness from 20 to 1100 /spl Aring/ were prepared by radio- frequency reactive sputtering in an N/sub 2/--Ar mixture. The FeCoN films prepared in a low nitrogen flow rate percentage (<6%) and sputtering pressure (<8 mTorr) have a high B/sub s/ of about 24.0 kG, but a moderate hard-axis coercivity H/sub ch/ of 5-30 Oe. With further increase in N/sub 2/ percentage or sputtering pressure, films become significantly softer, with H/sub ch/ of about 0.1-0.6 Oe, and have a higher resistivity of up to about 160 /spl mu//spl Omega//spl middot/cm. The change in the magnetic properties with nitrogen flow rate percentage and sputtering pressure can be attributed to the formation of an ultrafine grain size nanocrystalline FeCoN thin film as observed by high-resolution transmission electron microscope. The soft properties of FeCoN films with nano-sized crystallites remain stable even after being annealed at 270/spl deg/C.     

Magnetoresistance and Magnetic Anisotropy Properties of Strain-Induced Co/Ag Multilayer Films

We report on the magnetoresistance (MR) properties of [Co(tCo)/Ag 1.5 nm]$_{20}$ multilayer and alloy films grown with the pulse electrochemical deposition on a polyamide substrate (1 cm$^{2}$ ). The induced uniaxial magnetic anisotropy was observed due to the effect of strain in all the multilayer films. The multilayer [Co 1.5 nm/Ag 1.5 nm]$_{20}$ showed a minimum hysteresis loss. The maximum MR ratio for Co/Ag was 9.2% at 1 kOe. A remarkable difference of magnetic field dependence of the magnetoresistance ratio was observed, corresponding to the orientation of magnetization curves.      

Preparation and properties of antiperovskite Mn3NiN thin film

The magnetic and electronic transport properties of the antiperovskite Mn₃NiN thin film deposited on quartz substrate using magnetron sputtering were investigated. The film shows a (100) preferred orientation. It is worthwhile noting that a positive magnetoresistance (MR) effect was found in the whole measured temperature region and the maximum MR value by 31% was obtained at about 300 K under 2 T. On the other hand, when cooling from room temperature, a spin-glass behavior was also observed in the Mn₃NiN film and the Tb shifted to lower temperature with increasing external magnetic field. In contrast to the bulk counterpart, the temperature dependent resistivity of the film shows a semiconductor-like behavior.     

Optical and electrical H/sub 2/- and NO/sub 2/-sensing properties of Au/In/sub x/O/sub y/N/sub z/ films

In this paper, we describe the optical and electrical gas-sensing properties of In/sub x/O/sub y/N/sub z/ films with an ultrathin gold promoter overlayer. We have fabricated In/sub x/O/sub y/N/sub z/ films with a nanocrystalline porous structure by RF-sputtering in Ar/N/sub 2/ followed by an annealing process. Gold particles with 20-30-nm diameter have been formed on top of the In/sub x/O/sub y/N/sub z/ films by dc sputtering and an annealing process. We have investigated the optical H/sub 2/and NO/sub 2/-sensing properties (change of absorbance) and also the electrical sensing effect (change of electrical resistance) for these two gases. A combined optical/electrical sensor for H/sub 2//NO/sub 2/ is proposed.     

Magnetoresistance in magnetic tunnel junctions with amorphous electrodes

Magnetic tunnel junctions (MTJs) with amorphous CoFeB and Co/sub 2/MnSi electrodes were fabricated and examined. In the case of [Co/sub 90/Fe/sub 10/]/sub 100-x/B/sub x/, the x=32% boron addition reduces the magnetization by 30% compared to Co/sub 90/Fe/sub 10/, yet the reduction of the tunnel magnetoresistance (TMR) is over 95%. On the contrary, in the case of Co/sub (100-x-y)/Mn/sub x/Si/sub y/, although net magnetization is very small at room temperature, the TMR can be as large as 7%. The character of each metalloid (boron and silicon) could be responsible for the peculiar behavior to each system.     

Wear resistance, mechanical strength and microstructure on sputtered CoCr perpendicular media

Wear resistance for sputtered CoCr perpendicular recording media has been investigated. Wear resistance and mechanical strength (tensile strength and Young's modulus) have been measured for CoCr (0-33 at% Cr) films deposited under various sputtering conditions. Furthermore, their correlations to CoCr film microstructures have been studied. The wear resistance on the CoCr films strongly depends upon the mechanical strength, and their relationship can be explained in terms of Archard's adhesive wear theory. Wear resistance and mechanical strength for CoCr (5-33 at% Cr) films decrease steeply at high sputtering Ar pressure. However, those for pure Co films are independent from sputtering pressure. Microstructure analyses for CoCr and pure Co films indicate that a main factor reducing the wear resistance and the mechanical strength is Cr segregation in the CoCr films.     

Influence of annealing on magnetic, relaxation and structural properties of composite and multilayer films

This work is devoted to the research of influence of annealing to ferromagnetic resonance (FMR) properties of films of the A, B series with the compositions of (Co45-Fe45-Zr10)x(Al2O3)y, multilayer films of the D series with compositions {[(Co45-Fe45-Zr10)x(Al2O3)y]-[alpha-Si]}120 and revealing their relationship with the nanostructure characteristics. The films were obtained in an argon atmosphere (the A, D series) and with addition of oxygen (the B series). All samples were deposited on substrates by the ion-beam sputtering method and were annealed. The resonant fields and width of ferromagnetic resonance (FMR) line were measured before and after annealing. The changes in the FMR field and width of the line at varying temperatures of annealing for the composite and multilayer films are analyzed in the work. The character of changes in the structural characteristics of films at different annealing temperatures is determined.     

掺杂Mg对纳米CoFe2O4/SiO2复合薄膜结构和磁性的影响

采用溶胶-凝胶旋涂法制备了纳米Co_1-xMg _xFe₂O₄/SiO₂(x = 0, 0.2, 0.4, 0.6, 0.8) 复合薄膜。利用XRD、SEM、原子力显微镜、振动样品磁强计对薄膜的结构、形貌和磁性进行了分析, 研究了Mg²⁺含量对样品结构和磁性的影响。结果表明, 样品中Co_1-xMg _xFe₂O₄具有尖晶石结构, 晶粒尺寸在38~46 nm之间。随着Mg²⁺含量的增加, Co_1-xMg _xFe₂O₄的晶格常数减小, 样品的饱和磁化强度减小, 矫顽力先增大后减小。样品Co_0.4Mg_0.6Fe₂O₄/SiO₂垂直和平行膜面的矫顽力分别为350.7 kA·m^-1和279.4 kA·m^-1, 剩磁比分别为67.2%和53.9%, Co_1-xMg _xFe₂O₄/SiO₂复合薄膜具有较明显的垂直磁各向异性。     

Co-Fe metal/native-oxide multilayers: a new direction in soft magnetic thin film design II. Microscopic characteristics and interactions

Co/sub x/Fe/sub 100-x/ metal/native-oxide multilayer (MNOM) films exhibit soft magnetic properties, large magnetization, high resistivity, and a potential operating bandwidth of several gigahertz. These attractive characteristics are facilitated by ultrathin magnetic native oxide layers introduced to provide a high-resistivity barrier between nanocrystalline metal layers while preserving interlayer coupling and contributing to the net moment. This paper addresses several important features of the MNOM system from a microscopic perspective. The uniaxial anisotropy of MNOM thin films is discussed in detail and "exchange averaging" is invoked to account for its vanishingly small effective dispersion. The role of the native oxide in establishing interlayer exchange coupling is demonstrated, and a detailed account of the nature of the oxide is presented. In the Fe MNOM system, the oxide is shown to have a volume-averaged magnetization of 732(35) emu/cm/sup 3/, with a temperature dependence comparable to that of metallic Fe. The magnetism of this largely "interfacial" oxide is supported by the metal and collapses in the absence of the metal. The oxide retains a large net moment for Co fractions up to at least x=50, but oxide magnetism is lost at high Co fractions, coinciding with the loss of soft magnetic properties.     

Pt Content Dependence of Magnetic Properties of CoPt/Ru Patterned Films

The magnetic properties of dot arrays made of CoPt/Ru perpendicular films (20 nm thickness) were examined as a function of Pt content. The CoPt dot arrays with a dot size D of 140 nm showed a single domain state, after removal of the applied field equal to H_r. H_r decreased from 5.2 kOe to 3.0 kOe as the Pt content decreased from 20 at% to 14 at%. The angular dependence of H_r for these dot arrays indicated coherent rotation of the magnetization during nucleation. The effective magnetic anisotropy, including the demagnetizing energy due to the dot shape, K_u ^eff, decreased as the Pt content decreased, resulting in the H_r reduction. The values of the switching volume for nucleation, V_sw , evaluated from the stabilizing energy barrier E₀, were a few percent of the dot volume. The switching diameter for nucleation, D_sw, increased slightly as the Pt content decreased, which was qualitatively in good agreement with the increase in the exchange length of magnetization. The value of E₀/k _BT (k_B is the Boltzmann constant and T is the absolute temperature) reduced as the Pt content decreased; however, E ₀/k_BT still had a high of 440 even at 14 at% Pt content. We successfully demonstrated the reduction of H_r for CoPt/Ru patterned films on reducing the Pt content, while simultaneously maintaining a high thermal stability. A calculation based on the experimental results suggested the potential recording density of CoPt/Ru dot arrays used for patterned media to be over 1 Tb/in²      

Influence of Cr contents and nanograin sizes on microstructure, mechanical and sliding tribological behaviors of hard Cr-diamond-like carbon films

The influence of Cr content and nanograin size on the microstructure, the mechanical and sliding tribological behaviors of Cr-containing diamond-like carbon (Cr-DLC) films, deposited on (100) Si substrate by a mid-frequency dual-magnetron system, was explored. The Cr-containing nanoparticles (combining Cr with C) were dispersed in the amorphous DLC matrix while some nanoparticles were transformed into compounds of C/Cr. The incorporation of Cr into Cr-DLC films improved the crystallinity of the Cr-rich nanoparticles and partially converted the nanoparticles to Cr/C phase. The films with Cr content ranging between 5-10 at% and with Cr-containing nanograin sizes in range of 15-27 nm were found to possess higher hardness, lower intrinsic stress, lower coefficient of friction (COF) and wear rate than those of 16-28 at% Cr content and 46-74 nm nanograin sizes. The superhard Cr-DLC film with 8.3 at% Cr and 18.4 nm Cr-containing grain gave the favorable micro-tribological characteristics with COF at micro approximately 0.1 and wear rate at 3.6 x 10(-8) mm3/Nm.     

The comparative effect of two different annealing temperatures and times on the sensitivity and long-term stability of WO/sub 3/ thin films for detecting NO/sub 2/

We have deposited 150-nm-thick WO/sub 3/ films on Si/sub 3/N/sub 4//Si substrates provided with platinum interdigital electrodes and annealed in static air at 300/spl deg/C and 500/spl deg/C temperatures for 24 h and 200 h. The morphology, crystalline phase, and chemical composition of the films have been characterized using AFM, grazing incidence XRD and high resolution XPS techniques. The sensor resistance response curve has been obtained in the 0.2 -4 ppm NO/sub 2/ gas concentration range in humid air (50% relative humidity), varying the operating temperature between 25 and 250/spl deg/C. By plotting both sensor resistance and gas concentration logarithmically, the response is linear over the investigated dynamic range. Sensor sensitivities, here defined as the ratio of sensor resistance in gas to that in air (i.e., S=R/sub Gas//R/sub Air/), have been compared at a given NO/sub 2/ gas concentration (0.2 ppm). The long-term stability properties have been evaluated by recording film sensitivity for 1 yr under standardized test conditions. Increasing the annealing temperature from 300 to 500/spl deg/C causes the sensitivities to decrease. The 300/24h film is shown to be the most sensitive at S=233, but with poor long-term stability properties. The 300/200h film with S=32 is stable over the examined period. The 500/24 and the 500/200 films are shown to be less sensitive with S=16 and S=14, respectively. The longer the annealing time and the higher the temperature, the poorer the sensitivity, but with positive effects upon the long-term stability of the electrical response. The influence of the annealing conditions on sensitivity and long-term stability has been correlated with the concentration of surface defects, like reduced WO/sub 3/ phase (i.e., W/sup 4+/), which resulted in a strong effect on the sensors' response.