Magnetization in permalloy thin films

Thin films of permalloy (Ni₈₀Fe₂₀) were prepared using an Ar+N₂ mixture with magnetron sputtering technique at ambient temperature. The film prepared with only Ar gas shows reflections corresponding to the permalloy phase in X-ray diffraction (XRD) pattern. The addition of nitrogen during sputtering results in broadening of the peaks in XRD pattern, which finally leads to an amorphous phase. The M-H loop for the sample prepared with only Ar gas is matching well with the values obtained for the permalloy. For the samples prepared with increased nitrogen partial pressure the magnetic moment decreased rapidly and the values of coercivity increased. The polarized neutron reflectivity measurements (PNR) were performed in the sample prepared with only Ar gas and with nitrogen partial pressure of 5 and 10%. It was found that the spin-up and spin-down reflectivities show exactly similar reflectivity for the sample prepared with Ar gas alone, while PNR measurements on 5 and 10% sample show splitting in the spin-up and spin-down reflectivity.      

The electrical properties of thin permalloy films

The magnetic properties of thin Permalloy films have been the subject of many investigations, but the work on their electrical properties is very limited [1]. By observing the change in electrical resistance with temperature the structural transformations taking place during the annealing of the condensates can be inferred.The authors of [1] did not undertake a detailed study of the electrical properties of Permalloy. They used Permalloy 79NMA in their investigation, and the dependence of the change in electrical resistance on the temperature of annealing in a magnetic field enabled them to reach conclusions about the nature of the uniaxial anisotropy of thin films.In the present work a detailed study has been made of the electrical resistance of Permalloy films in relation to the temperature of the substrate during evaporation and annealing; the temperature coefficient of resistance (TCR) has also been studied.     

Argon and krypton ion-induced changes in permalloy thin films

The effects of 75-keV Ar and 100-keV Kr ion irradiations of 72-nm thin DC-sputtered permalloy (Ni₈₁Fe₁₉) films on Si(100) wafers were studied at fluences of up to 10¹⁶ ions/cm². The changes of the structural and magnetic properties were measured via X-ray diffraction, Rutherford backscattering spectroscopy, and magneto-optical Kerr effect. The irradiations increase the lattice constant and improve the crystallinity of the samples. They induce also strong changes of the magnetic polarisation and the coercive field for increasing ion fluence. The hysteresis loops suggest that, with increasing ion fluence, the reversal of the magnetisation changes gradually from rotation-dominated in the as-deposited films to domain-wall-motion dominated at the highest ion fluences. The results are compared with those obtained for Ni-, Cr-and Xe-ion irradiated permalloy films.     

Domain structure of “transcritical” films of permalloy

The domain structure of transcritical films of permalloy between 0·5 and 40 m thick has been studied by the powder method. A zigzag curvature of domain walls has been found ath> >3 m. The effect of external magnetic fields on powder depositions has been investigated, a model of domain structure supposing the closing of magnetic flux being proposed.Submitted for publication, not presented at the IVth ICMTF.     

Comparison of the soft magnetic properties of permalloy and conetic thin films

The soft magnetic properties of the substrate/[non-buffer or buffer Ta]/[permalloy (Ni₈₀Fe₂₀) or conetic (Ni₇₇Fe₁₄Cu₅Mo₄)]/Ta prepared by ion beam sputter deposition are investigated. The value of the surface resistance of the conetic film is twice as high as that of the permalloy film. The value of the coercivity and magnetic susceptibility of the conetic film decreased by 25% and doubled relative to that of the permalloy film. The coercivity, with a value of 0.12 Oe, and the magnetic susceptibility, with a value of 1.2×10⁴ for the conetic film, are suitable for soft magnetic biosensor applications.     

Vibrational spectra of thin eulytine films

This is a study of IR reflection spectra of systems of a thin Bi₄X₃O₁₂(X=Si, Ge) film and a substrate of fused quartz v-SiO₂ in the range 400–1600 cm⁻¹ at T=295 K. Bands assigned to Bi₄X₃O₁₂ are interpreted. It is found that single-photon processes are exhibited in the range 400–800 cm⁻¹, while biphonon processes, in the range 800–1600 cm⁻¹. I. Franko State University of Lvov, 50 Dragomanov St., 290005, Lvov, Ukraine. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 64, No. 4, pp. 494–498, July–August, 1997.     

Low-frequency Raman spectra of paradichlorobenzene thin films

The low-frequency Raman spectra of paradichlorobenzene nanofilms with a thickness of about 30 μm, 1 μm, and 400 nm are experimentally measured. With decreasing film thickness, the spectral lines shift to lower frequencies and broaden and some additional lines appear, the intensity of which increases with decreasing film thickness. The film structure is modeled using the method of molecular dynamics, and the histograms of lattice vibration spectra are calculated by the Dean method. It is found that a decrease in the film thickness leads to an increase in the lattice parameters and to a higher orientational disorder both inside the film and, especially, at the film surface. The film structure is similar to the structure of the α-paradichlorobenzene single crystal. To correctly interpret the spectra of lattice vibrations, it is necessary to take into account surface vibrations and existence of vacancies in the structure.     

Magnetism in very thin films of permalloy measured by spin polarized cascade electrons

The spin polarizationP of the low energy cascade electrons excited with a primary unpolarized electron beam is measured with ultrathin films of permalloy (Ni₈₀Fe₂₀) as a function of film thickness, external magnetic field, and temperatureT. Surface adsorbates of small concentrations of less than 10% of a monolayer can change the Curie point and the saturation value ofP ₀(T0) by as much as 30%. The Ta-substrate induces a magnetically dead region in permalloy. Conventional spin wave theory cannot account for the observed smallT-dependence of the magnetizationM. Films on a nonmagnetic substrate are compared to similar films coupled to bulk permalloy over an interface of Ta. TheT-dependence ofM with the coupled films can be explained by spin wave theory. At lowT, the films coupled to the bulk exhibit a faster decrease ofM than the uncoupled films. We propose that this thermal stabilization of the magnetization in very thin ferromagnetic films is due to quenching of the long wavelength spin modes.     

Phonon emission spectra of thin metallic films

Thin metallic films evaporated on an Al₂O₃-single crystal and cooled to liquid helium temperatures are heated by short electric current pulses. The high frequency part of the emitted phonons is detected by calibrated superconductive tunneling junctions on the opposite surface of the substrate. The observed phonon detector signal amplitude is compared with theoretical models taking account of the boundary conditions for elastic waves in the film. It is found that the phonon spectrum emitted perpendicularly to the substrate-film boundary depends strongly on the thickness of the heater film.     

Transmission spectra of bismuth trioxide thin films

Transmission spectra of bismuth trioxide thin films, of tetragonal and ortorhombic structures, are studied. Experimental data on the wavelength dependence of the refractive index are presented. The dispersion of the refractive index follows a single-oscillator model. Optical energy gap of tetragonal phase is smaller than that of orthorhombic phase; at 300 K these are 2.6 eV and 2.85 eV and at 77K are 2.8 and 3.1 eV, respectively.     

Thermal emission spectra of CaF2 thin films

Thermal emission spectra of CaF₂ thin films evaporated on Pt plates are measured at elevated temperatures. P-polarized spectra observed at the emission angle of 25° show sharp peaks around phonon frequencies. Considerable changes in the spectra are found for films prepared under different conditions. The spectra of a film heat-treated at 680°C are analysed using the response function based on the virtual-mode theory for ionic slabs, in order to estimate the temperature dependence of the lattice dynamical quantities such as phonon frequency and damping. The temperature dependence is discussed in terms of a theory of phonon anharmonicity.     

Spin-wave eigenmodes of permalloy squares with a closure domain structure

Quantized spin-wave eigenmodes in single, 16 nm thick and 0.75 to 4 mum wide square permalloy islands with a fourfold closure domain structure have been investigated by microfocus Brillouin light scattering spectroscopy and time resolved scanning magneto-optical Kerr microscopy. Up to six eigenmodes were detected and classified. The main direction of the spin-wave quantization in the domains was found to be perpendicular to the local static magnetization. An additional less pronounced quantization along the direction parallel to the static magnetization was also observed.     

Magnetoresistance measurement of permalloy thin film rings with triangular fins

Magnetization reversals in permalloy rings controlled by nucleation sites using triangular fins at the same side and diagonal with respect to the field direction are demonstrated by magnetoresistance measurement and micromagnetic simulation. In the ring with triangular fins at the same side, there exists two-step reversal from onion to flux-closure state (or vortex state) and then from flux-closure (or vortex state) to reverse onion state; in the ring with diagonal triangular fins, one-step reversal occurs directly from onion to reverse onion state. The reversal processes are repeatable and controllable in contrast to an ideal ring without triangular fins where one-step and two-step reversals occur randomly in sweep-up and sweep-down processes.     

Conversion electron Mossbauer spectra of very thin gold films

Conversion electron Mössbauer spectroscopy of the 77.3 keV transition in¹⁹⁷Au is shown to be three orders of magnitude more sensitive than the usual gamma-ray transmission technique. CEMS spectra of metallic gold films as thin as 10–100 μg/cm² (i.e. 5–50 nm) were measured.     

Properties of permalloy films produced in low-temperature plasma flows with a controlled composition

A simple version of a flow-forming plasma sputtering system is proposed. The causes that determine the properties of the deposited films are revealed when the composition, energy, and particle density of the flow are controlled. The electron component of the plasma flow and an increase in its ion component are found to degrade the magnetic properties of the films. The ferromagnetic resonance (FMR) line half-width of 10- to 150-nm-thick films is shown to mainly depend on the energy of the neutral flow component, which is specified by the sputtering conditions at an anode voltage of 400–700 V. In this rather narrow energy range, the FMR line half-width is 25 Oe for cold substrates.     

Picosecond control of coherent magnetisation dynamics in permalloy thin films by picosecond magnetic field pulse shaping

We have measured the response of a 20×10 μm, 8 nm thin NiFe (80:20) permalloy film due to excitation by short in-plane magnetic field pulses. We will show that using a two-pulse-technique a complete control of the precessional motion of the magnetisation can be achieved on picosecond timescales. Furthermore, we will present numerical calculations which show that a complete suppression of magnetisation ringing after switching can only be realised by a cascade of short field pulses.