The effects of metallic underlayers on Properties of permalloy films

Thin Permalloy films of zero-magnetostrictive composition were evaporated on a variety of metal film underlayers of various thicknesses (which were deposited on glass substrates) and also on smooth metallic substrates. In contrast to Prosen et al., however, the observed uniaxial magnetic anisotropy is not zero. In thin Permalloy films (100-1000 Å) deposited on high melting-point metal films (Mo, Ti, Pd, and Cr), essentially the same anisotropy field is obtained as is normally observed on glass substrates. In these films the coercivity and the angular dispersion increase slightly as the underlayer thickness increases. Permalloy properties on low melting-point metals (Au, Ag, Cu, and Al) depend strongly upon the underlayer thickness. At a given substrate temperature, a maximum in coercivity and angular dispersion is found in ∼100 Å thick underlayers of Au, Ag, and Cu. In Al underlayers, the values of coercive force along the easy and hard axis increase rapidly as a function of thickness. Large values of the easy-axis skew are obtained in all metal underlayers where the direction of the skew depends upon the geometrical arrangement of the vapor source (Permalloy) and the substrate. These effects are attributed to the microstructure and morphology of the underlayers. Electron microscopy studies are presented in confirmation of these surface geometrical effects.     

Effect of microstructural evolution on magnetic properties of Ni thin films

The magnetic properties of Ni thin films, in the range 20–500 nm, at the crystalline-nanocrystalline interface are reported. The effect of thickness, substrate and substrate temperature has been studied. For the films deposited at ambient temperatures on borosilicate glass substrates, the crystallite size, coercive field and magnetization energy density first increase and achieve a maximum at a critical value of thickness and decrease thereafter. At a thickness of 50 nm, the films deposited at ambient temperature onto borosilicate glass, MgO and silicon do not exhibit long-range order but are magnetic as is evident from the non-zero coercive field and magnetization energy. Phase contrast microscopy revealed that the grain sizes increase from a value of 30–50 nm at ambient temperature to 120–150 nm at 503 K and remain approximately constant in this range up to 593 K. The existence of grain boundary walls of width 30–50 nm is demonstrated using phase contrast images. The grain boundary area also stagnates at higher substrate temperature. There is pronounced shape anisotropy as evidenced by the increased aspect ratio of the grains as a function of substrate temperature. Nickel thin films of 50 nm show the absence of long-range crystalline order at ambient temperature growth conditions and a preferred [111] orientation at higher substrate temperatures. Thin films are found to be thermally relaxed at elevated deposition temperature and having large compressive strain at ambient temperature. This transition from nanocrystalline to crystalline order causes a peak in the coercive field in the region of transition as a function of thickness and substrate temperature. The saturation magnetization on the other hand increases with increase in substrate temperature.     

An electroplated 84Fe-5Ni-11Cu isotropic thin film for the cubic waffle-iron

The information storage media in the cubic waffle-iron memory is a square loop, isotropic, medium coercive force planar film called the overlay, which is placed in contact with ferrite posts. An 84Fe-5Ni-11Cu alloy has been developed to meet the requirements of the waffle-iron overlay. The film is electrodeposited on a specially prepared2 frac{1}/{2}by1 frac{1}/{4}by 0.040 inch copper substrate. The basic waffle-iron cell has an area of 30 mils by 30 mils, yielding a storage density in the film of 1100 b/in². The film has a coercive force of 10 Oe, 0.9 squareness ratio, 7000-Å thickness, and 0.52 Oe-μs switching coefficient. The preparation technique of the substrate has resulted in a 75-percent yield of films in which every bit output exceeds a level of 5 mV. Operational data has shown output uniformity to be maintained within ±10 percent. A corrosion study at 95°F and 90-percent humidity of eight protective coatings has resulted in the choice of Acryloid lacquer as the protective coating for the iron-rich alloy. This coating, which is applied evenly by a controlled dipping process, also provides electrical insulation between the film and the drive windings. Preliminary results of a six-month aging study at 60°C show no significant change in the hysteresis loop of the films.     

Magnetic properties and creep observations of Ni-Fe films 30 to 300 Å thick

Coercivity, induced uniaxial anisotropy field, angular dispersion, residual stress, magnetic domain wall, and magnetization creep of vapor-deposited 81.7 Ni-18.3 Fe films are reported. The thickness and temperature dependence of the coercivity and the induced uniaxial anisotropy field in the thickness range from 30 to 16 000 Å are described. A substrate temperature range is given for minimum residual stress. Lorentz micrographs of magnetic domain walls and magnetization creep of films in the thickness range from 30 to 300 Å are presented. It has been found that Néel walls creep under the influence of a unipolar hard-axis field pulse in the presence of a constant dc easy-axis field. The paper discusses the experimental results in the light of existing creep theories.     

The dependence of the magnetic properties of non-magnetostrictive NiFeCo films on the deposition conditions of aluminium underlayers

Results are presented which describe the effect of the deposition parameters of aluminium underlayers on the magnetic properties of non-magnetostrictive NiFeCo films. Three aluminium film deposition parameters were considered: evaporation rate, substrate temperature and film thickness. The effects of these parameters on the structure of the aluminium film and on the coercivity, angular dispersion, anisotropy field and saturation magnetization of the subsequent magnetic film in the thickness range 0.06–0.5 μm are reported.A correlation of the angular dispersion with underlayer grain size was established experimentally and is explained in terms of a linear micromagnetic theory of dispersion.     

Influence of substrate temperature and film thickness on the structure of reactively evaporated In2O3 films

Indium oxide films 25–550 Å thick were reactively evaporated at an oxygen pressure of about 0.27 Pa and at a substrate temperature between room temperature and 400°C. The dependence of the structure of the films on the substrate temperature and on the film thickness was studied using transmission electron microscopy and electron diffraction. It was found that thick films (about 550 Å) were amorphous at room temperature, partially crystallized at 50–125°C and crystalline at 150–400°C. The crystallinity of the films deposited at 150–250°C also depended markedly on the film thickness. Very thin films about 25 Å thick were quasi-amorphous, but with increasing film thickness the amorphous phase transformed into a crystalline phase.The thermal transformation of the amorphous films after deposition was also studied. Amorphous films about 550 Å thick deposited at room temperature and 100°C crystallized at 230°C and 210°C respectively.     

2.24 Structural and electrical properties of discontinuous gold films on glass

In the present work thin gold films are investigated in the thickness interval 10–160 Å. The films are deposited in UHV on to glass substrates at room temperature and with an electric field in the substrate plane. In the thickness interval 10–45 Å the film is discontinuous and the size distribution of the islands as determined from electron micrographs is described with a log-normal distribution function. The onset of the in situ electrical conduction at the average thickness 45 Å makes it possible to measure the film resistance as a function of the film thickness during the condensation. At the thickness 53 Å stable metallic continuous paths are formed and the film achieves metallic properties. The fraction of the surface covered with material and the island density are measured 20 h after the deposition. Both these entities change rapidly at the stage when the film grows to be metallic continuous.     

Crystallization of amorphous antimony films on silver films

The crystallization process in amorphous antimony films 70–330 Å thick evaporated onto silver films 10–150 Å thick which have previously been evaporated onto glass is directly observed through an optical microscope. The conditions under which the crystallization process in the amorphous antimony films is observed are found to be severely limited by the preparation conditions of the silver films. The crystallization can only be observed on silver films thinner than 30–40 Å which have previously been exposed to oxygen or nitrogen gas. The crystallization thickness of amorphous antimony films on these substrates is estimated to be 123-75 Å as the substrate temperature varies from 20 to 80 °C and the activation energy for crystallization to be 0.23-0.30 eV as the film thickness varies from infinity to 200 Å.     

Magnetic properties of sputtered multilayers of Mo/Ni

We have studied the d.c. magnetization of Mo/Ni artificial superlattices in the temperature range 5–300 K and in magnetic fields of up to 10⁷/4πAm^-1 (10kG). The saturation magnetization and the Curie temperature behavior are consistent with expectations based on thin film effects. However, there are indications of ferromagnetic coupling across the normal metal and the coercive field shows an unexpected peak at a layer thickness of 25 Å.     

The preparation and properties of electrodeposited permalloy films on substrates of evaporated permalloy

The technology of production and some of the properties of isotropic magnetic Ni 80%-Fe 20% films are described. These films were obtained by permalloy electrodeposition onto glass substrates previously coated with vacuum-deposited thin films of Ni-Fe alloy. The change in the magnetoresistance of the films as a function of thickness has been investigated and is discussed, taking into account the influence of the film composition. The results are compared with those previously reported for evaporated films. The dependence of coercive force on film thickness is given. An increase in the crystallite size of the electro-deposited films with respect to the vacuum-deposited substrate has been found.     

Nonlinear domain-wall velocity and coercive force in permalloy films

Domain wall velocities are measured for 2700 Å and 2200 Å thick Permalloy films of several coercive forces. The velocity-drive field curves are characterized by two mobilities, as often reported. It is found that these low- and high-field mobilities are strongly affected by coercive force of the films. The low-field mobility is nearly constant for low-coercive-force films, and decreases rapidly with increasing coercive force. The high-field mobility is inversely proportional to the coercive force. The measured results suggest that the nonlinear dependence of wall velocity on drive field would disappear in a zero-coercive-force film. None of the mechanisms proposed up to now can explain this behavior of wall velocity in Permalloy films. The nonlinearity is attributed to the transition of material inhomogeneities from pinning centers in low field to dissipation centers in high field.     

Stripe domains in electrodeposited NiCo thin films

The presence of stripe domains (SD) in electrodeposited NiCo thin films was inferred from the specific form of the hysteresis loops. The critical field H_cr of this type of magnetization domain has been studied as a function of film composition, film thickness and annealing temperature. The range of the experimental parameters was: composition 0–50% Co in nickel, thickness 300–1000 nm and annealing temperature 300°–525°K.The experiments have shown that the magnetostriction-stress interaction (Saito et al.) and the columnar growth of crystallites separated by non-magnetic boundaries (Iwata et al.) are the two main causes for SD.     

Random Magnetic Anisotropy Studies in SmCo<Subscript>5</Subscript> Thin Films

SmCo₅ thin films with different thicknesses were prepared by electron beam evaporation on Kapton substrates. The out-of-plane hysteresis loops for different thicknesses reveal a maximum coercive field when the thickness is 15 nm. Using random magnetic anisotropy model, the thickness dependence of magnetic properties was studied in SmCo₅ nanocrystalline films and several fundamental magnetic parameters were extracted. We have determined the local magnetic anisotropy constant K ₁ which is found to increase with increasing film thickness except for t =?7 nm which is thought to arise from the structural imperfection of the SmCo₅ films.     

Structure and magnetic properties of Fe films with pyramid-like nanostructures deposited by oblique target direct current magnetron sputtering

Fe thin films were deposited by oblique target direct current magnetron sputtering on Si (100) and (111) substrates. The structure, surface morphology and magnetic properties of the thin films were characterized using X-ray diffraction, field emission scanning electron microscopy, and superconducting quantum interference device magnetometer, respectively. The results reveal that the structure of the as-deposited Fe thin films is body-centered cubic with the preferential [110] crystalline orientation. A pyramid-like nanostructure with sharp tip was formed on the surfaces of Fe thin films under appropriate sputtering power. Formation of the pyramid-like nanostructure is mainly owed to the enhancement of atomic mobility and the bombardment effect with increasing of sputtering power. Meanwhile, the crystalline orientation of Si substrate and the intrinsic stress in the films are expected to have little contribution to the formation of the pyramid-like nanostructure. The magnetic anisotropy was found in the as-deposited Fe thin films, and varies with the thickness of the Fe thin films. As the film thickness increases from 604 to 1,786 nm, the magnetic anisotropy field and the uniaxial anisotropy constant increase from 3.8 to 5.6 kOe, and from 0.4 × 10⁶ to 1.1 × 10⁶ erg/cm³, respectively, which indicates that besides magnetocrystalline anisotropy, stress induced anisotropy and shape anisotropy also exist in the as-deposited Fe thin films.     

Magnetic properties of sputtered soft magnetic Fe–Ni films with an uniaxial anisotropy

The microstructure and magnetic properties of polycrystalline Fe_100−xNi_x films have been studied by X-ray diffraction (XRD) and magnetic moment measurements. In the XRD pattern of Fe–Ni films, the values of area ratio, A(1 1 1)/A(2 0 0) for the XRD peaks, in the thickness dependence decrease rapidly with increasing film thickness in the films with a bias field applied parallel to the plane in order to introduce uniaxial anisotropy, but the values for the films without the field are nearly constant. The coercivity vs. thickness analyzed by using Néel's formula show that the values for the films with the bias field follow Néel's formula within the thickness range of 40–100 nm, except the range of 10–40 nm. This result indicates that there is a change in domain wall type at the thickness of 40 nm. From the results of thickness and temperature dependence of magnetization analyzed by using some theoretical models, the values of interaction strength between magnetic ions were determined. The electrical resistivity of films is found to be consistent with the Mayadas–Shatzkes model.     

Microstructural features of Cd0·8Zn0·2Te thin films studied by X-ray diffraction and electron microscopy

Thin films of synthesized Cd_0·8Zn_0·2Te have been deposited on glass substrate at different substrate temperatures. Different microstructural parameters like crystallite size, rms strain, dislocation density, stacking fault probability and stacking fault energy are determined by XRD, SEM, TEM and TED. XRD and XPS have been used to determine the composition. Variations of the microstructural parameters with film thickness and substrate temperature have been studied in order to obtain optimum growth condition for maximum particle size and least microstructural defects. An effort has been made to correlate the experimental results.     

Studying the mechanism of exchange coupling in ferro/ferrimagnet NiFe/DyCo film structures

Dependence of the magnetic and magnetooptical properties of an exchange-coupled NiFe/DyCo bilayer system on the thickness (t _DyCo) of a magnetically hard layer has been studied. It is established that the unidirectional anisotropy vanishes at t _DyCo ～ 400 Å, while the coercive field in the magnetically soft layer becomes comparable to the exchange-induced field shift. In this case, the DyCo layer magnetization is almost parallel to the film plane, whereas a reference DyCo film exhibits a perpendicular anisotropy. A model of the magnetic state of layers in the ferro/ferrimagnetic layer structure under consideration is proposed, which assumes that a 180° domain wall is formed at the interface upon magnetization reversal in the magnetically soft layer.     

Magnetic and magnetooptical properties of sputtered Fe5Si3films

Polycrystalline films of Fe5Si3have been prepared by RF sputtering from a sintered target composed of 62.5 at% Fe and 37.5 at% Si. The Faraday rotation and optical absorption were measured for these films in the visible and near infrared. At a wavelength of 6328Å, room-temperature absorption (corrected for reflection) and specific Faraday rotation are 3.7 × 10⁵cm^-1and 1.3 × 10⁵deg/cm, respectively. The rotation decreases with rising temperature and vanishes around 120°C, the Curie temperature of the films. From polar and in-plane hysteresis loop measurements the spontaneous magnetization is found to lie in the film plane. Square hysteresis loops are observed when the external field is applied in the plane of the film, and the in-plane coercive force decreases monotonically with temperature at an average rate of -2 Oe/°C as Tcis approached.     

Diffusion in Au-Ni thin films

The objective of this work was to determine experimentally the values of the surface diffusion parameters of Au-Ni thin films obtained by vacuum evaporation and by sputter deposition. Thin film diffusion couples with an edge-to-edge interface arrangement were employed in order to define the surface diffusion mechanisms better. Experimental results show that the frequency factor (diffusion constant) for evaporated films (1.5×10^-8 cm² sec^-1) is higher than that for sputtered films (1.1×10^-8 cm² sec^-1) and bulk material (bulk diffusion data). The values obtained for the thermal activation energy in evaporated films were one order of magnitude less than those obtained for bulk material. Sputtered thin films were found to have an activation energy over 20% higher than that for evaporated films. This discrepancy apparently occurs because of partial incorporation of sputtered atoms into the glass substrate. Measurements of thin film adhesion showed the same effect.Examination of the structural characteristics of the specimens showed that both sputtered and evaporated films 300 Å and more in thickness become completely microscopically continuous. Some variations in grain size were also observed. Sputtered films were found to have crystallite grains twice as large as those in films prepared by evaporation. Microphotographs showed that for films 300 Å thick the “evaporation-condensation” effect occurs in the overlapping zone.     

Optimization of the planar hall effect in ferromagnetic thin films for device design

The planar Hall effect, although directly related to the magnetoresistance effect, differs in its potential uses by the disposition of the sensing electrodes allowing an internal balance of the excitation voltage drop. An experimental study of ferromagnetic thin film conditions of evaporation, film thickness, composition and shape of the electrodes has been undertaken. Anisotropic Ni-Fe films with various additions of Pd, V, Co, Mo, showed a maximum planar Hall effect for the composition 86-percent Ni, 14-percent Fe. The optimization of the geometrical parameters of the electrodes and the magnetic film elements is described, allowing one to design for maximum output voltage or maximum output current in a short circuited loop. Two schemes are presented for implementation of small NDRO memories.