Reactions in Au/Nb bilayer thin films

The interdiffusion and intermetallic compound formation of Au/Nb bilayer thin films annealed at 200–400 °C have been investigated. The bilayer thin films were prepared by electron beam deposition. The Nb film was 50 nm thick and the Au film was 50–200 nm thick. The interdiffusion of annealed specimens was examined by measuring the electrical resistance and depth-composition profile and by transmission electron microscopy. Interdiffusion between the thin films was detected at temperatures above 325 °C in a vacuum of 10^-4 Pa. The intermetallic compound Au₂Nb₃ and other unknown phases form during annealing at over 400 °C. The apparent diffusion constants, determined from the penetration depth for annealing at 350 °C, are 3.5 × 10⁻¹⁵ m² s⁻¹ for Nb in Au and 8.6 × 110^7minus;15 m² s⁻¹ for Au in Nb. The Au surface of the bilayer films becomes uneven after annealing at over 400 °C due to the reaction.     

Reaction between permalloy and several thin metal films

To develop the electrode materials for thin permalloy film devices, the reactions between the permalloy Ni-19%Fe and several metal films were investigated. From the results of the annealing behaviour for thin bilayer films including the permalloy, it was clarified that aluminium, copper, chromium and gold films react with the permalloy below 250–350°C. However, molybdenum and tantalum do not react up to 400°C. Therefore it is considered that molybdenum and tantalum are good electrode materials for thin permalloy film devices.     

Magnetic properties of permalloy/permalloy-oxide multilayer thin films

Magnetic properties of permalloy/permalloy-oxide multilayer thin films are investigated. These thin films are prepared by a repeat of sputter deposition of permalloy thin film, followed by oxidation of the film surface. The total thickness of the permalloy thin films before oxidation is about 100 nm. The number of layers is one to twenty. The oxide layers are formed by oxidation in dry air. The estimated oxide layer thickness is about 2 nm. The oxide NiFe₂O₄ is identified by RHEED. The film coercivity decreases linearly with increasing layer numbers. The saturation magnetization and magnetoresistivity decrease as the number of layers increase. The coercivity decrease is due to grain growth suppression and magnetic separation by oxide film of permalloy layer, and magnetoresistivity decrease is due to electrical resistivity increase originating into electron scattering by the oxide layer.     

Annealing kinetics of thin permalloy films

Low-temperature (250-397°C) annealing was found to cause a large decrease in the resistivity of radio-frequency sputter-deposited thin (≤ 500 Å) Permalloy films. A transmission electron microscope was used to investigate a probable microstructural change occurring during the annealing. It was found that the low-temperature annealing induced considerable grain growth in these films. Furthermore, an electron diffraction analysis has shown that this grain growth was accompanied by the formation of the ordered phase (Ni3Fe). The use of dark-field imaging revealed that the small ordered region appears to be formed around the disordered regions via a grain-boundary diffusion mechanism. The observed resistivity decrease was proposed to occur by the structural ordering as a result of the annealing. The measured activation energy for this process was 0.72 eV. This activation energy appears to be associated with the grain boundary migration of excess vacancies trapped during film formation.     

Bias susceptibility measurements in thin permalloy films

Susceptibility measurements at 5000 Hz have been performed in the easy and hard directions on two 80-20 Permalloy films (1000 Å, 1 cm in diameter) cut from large samples. The experimental results agree with the predictions of the Hoffmann theory. The susceptibility parallel to the average direction ofMis found to be proportional to1/(H - H_{k})^{7/4}or1/(H_{k} - H)^{7/4}when the net field is large enough to prevent blocking.     

Magnetic and magnetoresistive properties of sputtered permalloy thin films

The dependence of the magnetic properties, especially magnetoresistivity, of sputtered permalloy thin films on the sputtering Ar pressure is studied. The Ar pressure is varied between 0.106 and 1.06 pa. The coercivity and the electrical resistivity of permalloy films both remain stable in this pressure range. These two properties are dependent on the grain size of a permalloy film, which is independent of the Ar pressure in this pressure range. The average grain size is 10–12 nm in diameter. The magnetoresistivity decreases and the anisotropy field increases as the Ar pressure decreases. Magnetoresistivity is related to the preferred orientation of the sputtered permalloy film. The permalloy films deposited at high Ar pressures have no preferred orientation; therefore, they show high magnetoresistivity.     

Ion beam mixing of Ni/Ti bilayer thin films

Amorphization by ion beam mixing of bilayered samples consisting of nickel and titanium layers, each 50 nm thick, has been studied by selected area electron diffraction, plan and cross-sectional view transmission electron microscopy and Rutherford backscattering spectroscopy. Amorphization occurred on irradiation with 1 MeV Au⁺ ions at fluences ranging from 3 × 10¹⁹ to 2 × 10²⁰ m ⁻². Cross-sectional transmission electron microscopy revealed that amorphization starts close to the original Ni-Ti interface. It has been shown that collisional processes alone cannot account for the observed amount of mixing. A model based on thermodynamics has been found to predict an amount of mixing higher than that observed experimentally.     

The reduction of magnetism during the electrodeposition of thin permalloy films

The paper includes a new aspect on elimination of the composition gradient in electrodeposited magnetic thin films. By addition of cathodically reducible ions of antimony, selenium, or tellurium to the electrolyte, it is possible to incorporate these non-magnetic elements in the initially deposited film zones preferably. Because of the high amount of the nonmagnetic element these inhomogeneous zones of the ternary Permalloy film become non-magnetic and do not affect the homogeneous zones of the film used for storage purposes. Besides the examined systems Ni-Fe-Sb, Ni-Fe-Se and Ni-Fe-Te, some other ternary or quaternary systems given in a forecast may show this effect. Experimental conditions and data support the investigations.     

The optical properties of zirconium diboride thin films

The optical properties of evaporated thin films of zirconium diboride were investigated from 4.1 to 11.3 eV. The optical constants were determined by reflectance measurements made at near-normal and oblique angles of incidence. The existence and energy of interband transitions and the plasma frequency are inferred from these results.     

Optical response and surface morphology of In/Ag bilayer thin films

In/Ag bilayer thin films were fabricated by maintaining the Ag layer thickness constant at 5 nm while varying the In layer thickness between 3 and 30 nm. It was observed that the grain size in the films increased with increase in thickness. In the case of the single layer In films the grain size increased from 60 to 350 nm as the thickness increased from 3 to 30 nm while the grain size increased from 80 to 280 nm in as the bilayer thickness increased from 8 to 35 nm. There is a red shift in the plasmon resonance from 372 to 522 nm in the case of the pure In layers whereas it was from 492 to 618 nm for the bilayer system. The Ag single layers exhibit a plasmon resonance at 540 nm. On coupling the In and Ag layers in the bilayers, additional resonances appear in the spectrum. The origin of the additional plasmon resonance peaks can be traced to the excitation of localized surface plasmons.     

Mathematical models for loss measurements in thin permalloy films with ramp drives

Uniaxial thin Permalloy films are driven with a large amplitude sinusoidalHfield in order to approximate a ramp drive. TheHfield is characterized by rise times which exceed3 times 10^{6}Oe/s. Two mathematical models are suggested to represent the loss measurements obtained in a domain wall motion region and in an incoherent rotation region. A normalized loss threshold is determined which characterizes the transition between the two regions. In the slow reversal or wall motion region, the normalized losses are proportional to the square root of α whereH = alpha t. In the relatively fast reversal or incoherent rotation region, the normalized losses are proportional to α. In both cases the inverse switching time is proportional to the coercive force in excess of the static value. Experimental data verify the reasonableness of the mathematical models.     

Study of annealing effects in Al-Sb bilayer thin films

In this paper, we present preparation and characterization of Al-Sb bilayer thin films. Thin films of thicknesses, 3000/1000 Å and 3000/1500 Å, were obtained by the thermal evaporation (resistive heating) method. Vacuum annealing and rapid thermal annealing methods were used to mix bilayer thin film structure. Results obtained from optical band gap data and Rutherford back scattering spectrometry showed mixing of Al-Sb bilayer system.     

Study of annealing effects in In-Sb bilayer thin films

The thin films of In-Sb having different thicknesses of antimony keeping constant thickness of indium was deposited by thermal evaporation method on ITO coated conducting glass substrates at room temperature and a pressure of 10⁻⁵ torr. The samples were annealed for 1 h at 433 K at a pressure of 10⁻⁵ torr. The optical transmission spectra of as deposited and annealed films have been carried out at room temperature. The variation in optical band gap with thickness was also observed. Rutherford back scattering and X-ray diffraction analysis confirms mixing of bilayer system. The transverse I-V characteristic shows mixing effect after annealing at 433 K for 1 h. This study confirms mixing of bilayer structure of semiconductor thin films.     

Annealing behaviour and magnetic properties of Co/Pt and Fe/Pt bilayer thin films

The annealing behaviour and magnetic properties of Co/Pt and Fe/Pt bilayer thin films are investigated. The coercivity of Co/Pt bilayer thin films increases with annealing above 450 °C and shows a peak value of 40 kA m⁻¹ in the range from 500 to 550 °C. This increase is due to both the formation of a CoPt solid solution and the optimization of grain diameters. Furthermore, the increase is promoted by multilayering. Similar results were obtained for Fe/Pt bilayer thin films.     

The preparation of permalloy 80/20 thin films using a pulsed DC discharge in a hollow cathode

Permalloy thin films have many applications as sensors and actuators but the preparation of magnetic films by magnetron sputtering is problematic since the target material reduces or changes the magnetic configuration of the magnetron. Hollow cathode discharges can produce similar or greater plasma densities to that found in magnetron sputtering and can therefore be operated over a similar pressure range. Pulsed DC sputtering has been seen to have some advantages compared to DC or RF sputtering. In this paper we report the use of a combination of pulsed DC sputtering with a hollow cathode system to prepare thin films of Permalloy. The deposition rate was found to strongly depend on the gas flow used to prepare the thin films. Combinations of the experimental conditions were found to produce films with a (111) preferential crystal orientation and that the grain size of the crystals was mainly determined by the deposition rate. Furthermore, changes in the degree of ion bombardment did not appear to have any significant affect on the structure of the deposit.     

Interface and temperature dependent magnetic properties in permalloy thin films and tunnel junction structures

Magnetization dynamics and field dependent magnetization of different devices based on 25-30 nm thick Permalloy (Py) films: such as single Py layers (Py/MgO; Py/CoFeB/Al2O3) and Py inserted as a magnetic layer in magnetic tunnel junctions (Py/CoFe/Al2O3/CoFe; Py/CoFeB/Al2O3/CoFe; Py/MgO/Fe) have been extensively studied within a temperature range between 300 K down to 5 K. The dynamic response was investigated in the linear regime measuring the ferromagnetic resonance response of the Py layers using broadband vector network analyzer technique. Both the static and the dynamic properties suggest the possible presence of a thermally induced spin reorientation transition in the Py interface at temperatures around 60 K in all the samples investigated. It seems, however, that the details of the interface between Py and the hardening ferromagnet/insulator structure, the atomic structure of Py layers (amorphous vs. textured) as well as the presence of dipolar coupling through the insulating barrier in the magnetic tunnel junction structures could strongly influence this low temperature reorientation transition. Our conclusions are indirectly supported by structural characterization of the samples by means of X-Ray diffraction and high resolution transmission electron microscopy techniques. Micromagnetic simulations indicate the possibility of strongly enhanced surface anisotropy in thin Py films over CoFe or CoFeB underlayers. Comparison of the simulations with experimental results also shows that the thermally-induced spin reorientation transition could be influenced by the presence of strong disorder at the surface.