Microwave magnetic properties of soft magnetic thin films

We review our works that focus on the microwave magnetic properties of metallic,ferrite and granular thin films.Soft magnetic material with large permeability and low energy loss in the GHz range is a challenge for the inforcom technologies.GHz magnetic properties of the soft magnetic thin films with in-plane anisotropy were investigated.It is found that several hundreds of permeability at the GHz frequency was achieved for Co100-xZrx and Co90Nb10 metallic thin films because of their high saturation magneti...     

Electrodeposited Co-Pt thin films for magnetic hard disks

ew baths for Co-Pt electrodeposition have been developed and developed and ECD thin films (≤0.3μm) have been prepared and characterized structurally (XRD), morphologically (SEM), chemically (EDS) and magnetically (VSM); their improved corrosion, oxidation and wear resistance have been ascertained. Such alloys appear suitable candidates for magnetic storage systems, from all technological viewpoints. The originally formulated baths contain Co-NH₃-citrate complexes and Pt-p salt (Pt(NH₃)₂(NO₂)₂). Co-Pt thin films of fcc structure are deposited obtaining microcrystallites of definite composition. At Pt 30 at% we obtain fcc films with a=0.369 nm, H_C=80 kA m, and high squareness; increasing Co and decreasing Pt content in the bath it is possible to reduce the Pt content of the deposit, obtaining fcc structures containing two types of microcrystals with a = 0.3615 nm and a = 0.369 nm deposited simultaneously. NaH₂PO₂ additions to the bath have a stabilizing influence on the fcc structure of a = 0.3615 nm, Pt 20 at% and H_C as high as 200 kA/m, with hysteresis loops suitable for both longitudinal or perpendicular recording, depending on the thickness. We have prepared 2.5 in. hard disks for magnetic recording with ECD Co-Pt 20 at% with a polished and texturized ACD Ni-P underlayer. Pulse response, 1F & 2F frequency and frequency sweep response behaviour, as well as noise and overwrite characteristics have been measured for both our disks and high-standard sputtered Co-Cr-Ta production disks, showin improved D₅₀ for Co-Pt ECD disks. The signal-to-noise ratio could be improved by pulse electrodeposition and etching post-treatments.     

Critical behavior of magnetic thin films

We study the critical behavior of magnetic thin films as a function of the film thickness. We use the ferromagnetic Ising model with the high-resolution multiple histogram Monte Carlo (MC) simulation. We show that though the 2D behavior remains dominant at small thicknesses, there is a systematic continuous deviation of the critical exponents from their 2D values. We explain these deviations using the concept of “effective” exponents suggested by Capehart and Fisher in a finite size analysis. The shift of the critical temperature with the film thickness obtained here by MC simulation is in an excellent agreement with their prediction.     

Growth and characterisation of Eu doped GaN thin films

We have studied the optical properties of Eu doped GaN thin films. We have grown high quality Eu doped GaN thin films by using Gas Source Molecular Beam Epitaxy (GSMBE), with 1.4% Eu concentration. The Full Width at Half Maximum (FWHM) of the X-ray diffraction in an omega scan was found to be 288 arcsecs. Low Eu concentration (0.08%) doped GaN thin films were grown, where Eu-related photoluminescence at 622 and 613 nm was detected using above band-gap excitation at 2 K. For high Eu concentration of 30% GaN:Eu crystal photoluminescence (PL) and cathodoluminescence (CL) spectra show strong and intense transitions at 622 and 664 nm, but also at 593 nm for CL spectra, with a similar transition observed from the low Eu concentration sample.     

Synthesis and characterisation of co-evaporated tin sulphide thin films

Tin sulphide films were grown at different substrate temperatures by a thermal co-evaporation technique. The crystallinity of the films was evaluated from X-ray diffraction studies. Single-phase SnS films showed a strong (040) orientation with an orthorhombic crystal structure and a grain size of 0.12 μm. The films showed an electrical resistivity of 6.1 Ω cm with an activation energy of 0.26 eV. These films exhibited an optical band gap of 1.37 eV and had a high optical absorption coefficient (>10⁴ cm^-1) above the band-gap energy. The results obtained were analysed to evaluate the potentiality of the co-evaporated SnS films as an absorber layer in solar photovoltaic devices. PACS 78.40.Fy; 68.60.-p; 61.10.Nz; 68.55.-a; 78.66.-w     

Electrical resistivity due to electron scattering with magnetic domain walls and magnetic properties of Ni-Fe alloy thin films

The physical properties of magnetic domain walls and electrical conductivity of permalloy thin films under external magnetic fields were studied. Using a magnetic force microscope (MFM), we observed the variation of domain configurations with the change of applied magnetic field for different film thicknesses of 245, 320, and 415 nm. A superconducting quantum interference device (SQUID) was exploited to measure the magnetization loop for the applied magnetic field either parallel or perpendicular to the normal direction of the surface. We also found that the resistivity increases significantly as the electrical current conduction changed from parallel to perpendicular to the domain walls.     

Investigation of incoherent rotation in thin magnetic films by means of the stroboscopic electron microscope

This paper discusses some results of the investigation of dynamic domain structure arising in permalloy films during bidirectional incoherent rotation. It was found that at the beginning of the switching process the formation of the strip domains takes place. Then the process proceeds by breaking domain walls and growth of the switched areas.     

Depth profiling of copper thin films by resonant laser ablation

In Resonant Laser Ablation (RLA), material is related and selectively ionized by a low-energy pulse from a tunable laser. The selectivity and efficiency allow detection and quantitation at very low concentrations. We demonstrate that RLA has potential use in profiling thin layer and multilayer structures. Quantitative results are reported on the analysis of 20 and 100 Å copper thin films on Si(110) surfaces. Removal rates range from 10^–3 to 10^–2 Å/shot. Prospects for interrogation of dopants and impurities are also evaluated.     

In-situ conversion electron Mössbauer spectroscopy on Fe(110)-surfaces and thin films

Using in-situ conversion electron Mössbauer spectroscopy the layer-by-layer analysis of epitaxial 21-monolayer Fe(110)-films on W(110) was carried out. The hyperfine interaction parameters near the Ag-coated and free Fe(110) surfaces could be measured with the monolayer resolution. The quadrupole interaction deviates strongly from zero in the topmost iron monolayer. The reduction of hf-magnetic field for the free surface is demonstrated. The temperature dependence of the hf-magnetic field across the Ag-coated films is discussed.This work was supported by the Stiftung Volkswagenwerk.     

Secondary electron emission from thin carbon films

For the purpose of investigating how secondary electrons are produced in carbon, the correlation between energy-loss events and secondary electrons was studied experimentally by using the coincidence method. If a secondary electron is detected in coincidence with an electron transmitted through a thin film which has lost an amount of energy E, then the process causing this energy loss results in the production of secondary electrons. We established the existence of these coincidences and have taken inelastic and coincidence spectra for films of different thickness. We found that in carbon secondary electrons are predominantly produced as a result of energy losses of about 20 eV, with an efficiency of about 5%. The escape depth of secondary electrons was also estimated to be approximately 30 Å.     

Fabrication and electrical characterisation of Zr-substituted BaTiO3 thin films

Thin films of zirconium-substituted barium titanate were deposited by chemical solution deposition on platinum-coated silicon substrates at a temperature of 700 °C. The films showed a polycrystalline perovskite structure. The grain size was found to decrease with increase of Zr substitution. The effect of Zr substitution on the dielectric constant and the leakage was studied. It was found that with increasing Zr content the phase transition becomes diffuse and relaxor-like. The dielectric constant was also found to decrease with increasing amounts of Zr after an initial increase. The hysteresis loops became thinner and the remanent polarisation was found to decrease. The leakage behaviour was explained by Schottky theory. The barrier heights of the different films were calculated and found to vary between 1.12 eV and 1.19 eV. PACS 68.55.-a; 81.20.Fw; 77.84.Dy     

Inelastic electron scattering from thin metal films

I discuss the role of electron-hole pair excitation in inelastic scattering of slow electrons from thin metals films.     

XRD and XPS characterisation of transition metal silicide thin films

Binary transition metal silicides based on the systems Ti–Si, Fe–Si, Ni–Si and Cr–Si were fabricated on Si wafers by means of ion-beam co-sputter deposition and subsequent annealing. The crystalline structures of the phases formed were identified from the characteristic patterns acquired by means of X-ray diffraction (XRD) measurements. The phase formation sequences were described by means of the Pretorius' effective heat of formation (EHF) model. For the Ti–Si, Fe–Si and Ni–Si systems, single phase thin films of TiSi₂, β-FeSi₂ and NiSi₂ were generated as the model predicts, while a mixture of CrSi + CrSi₂ phases was obtained for the Cr–Si system. The surface chemical condition of individual specimens was analysed by using X-ray photoelectron spectroscopy (XPS). The chemical shifts of transition metal 2p_3/2 peaks from their metallic to silicide states were depicted by means of the Auger parameters and the Wagner plots. The positive chemical shift of 2.0 eV for Ni 2p_3/2 peak of NiSi₂ is mainly governed by the initial-state effects. For the other silicide specimens, the initial-state and final-state effects may oppose one another with similar impact. Consequently, smaller binding energy shifts of both negative and positive character are noted; a positive binding energy shift of 0.3 eV for the Fe 2p_3/2 level was shown for β-FeSi₂ and negative binding energy shifts of 0.1 and 0.3 eV were determined for CrSi + CrSi₂ and TiSi₂, respectively.     

The structure and magnetic properties of amorphous magnetic thin films

A review of the structural and magnetic properties of amorphous ferromagnetic and ferrimagnetic thin films is presented. An attempt is made to report structural information on atomic and microstructural scales, and to stress its relevance to the magnetic properties of these materials. The more obvious microstructural features of deposited films are not present in the other important type of amorphous magnetic material prepared by rapid quenching from the melt, and present opportunities for differences in structure dependent magnetic properties. In the main, three classes of amorphous magnetic films are considered. Ferromagnetic transition metal (TM) films which are metastable only at temperatures well below room temperature are discussed. Their importance lies in the fact that they clearly represent the most fundamental amorphous phase. Ferromagnetic transition metal-metalloid (TM-Me) alloys have potential applications as magnetically soft materials. These alloys are, perhaps, the most studied amorphous magnetic materials both in deposited thin film and rapidly quenched ribbon forms. Finally, amorphous rare earth-transition metal (RE-TM) films are reviewed. They exhibit a wide variety of magnetic properties encompassing both extremely low and very high coercivities and also perpendicular magnetic anisotropy. The possible application of these materials in various types of device has encouraged much detailed research into their magnetic properties. This has highlighted the importance of preparation conditions and microstructure in defining their properties.     

Kronig-Penney-type calculations for electron tunneling through thin disordered dielectric films

Kronig-Penney-type calculations were used to evaluate the tunneling probability through a thin disordered dielectric film between two metallic electrodes. Our calculations indicate that the tunneling probability increases with increasing disorder.     

First-order magnetic phase transitions in thin films

Using the simple Landau model, we discuss near-surface magnetic effects for thin films corresponding to first-order phase transitions. The size effects observed in ultrathin ferroelectric films are in agreement with this theoretical interpretation. The presence of a weak external field is also formulated. The text was submitted by the authors in English.     

Self-focusing magnetostatic beams in thin magnetic films

The possibility of generation of stable self-focusing beams in in-plane magnetized thin magnetic films is considered, and theoretical conditions for the existence of such localized solutions are discussed. It is shown that for the definite direction between static magnetizing field and preferential direction of radiation from a microwave antenna, the problem reduces to the one-dimensional nonlinear Schrödinger equation. For such angles it is possible to generate stable self-focusing beams. Particular values of beam width and propagation angles versus magnitude of magnetizing field are calculated in order to suggest a realistic experimental setup for the observing the discovered effect.Received: 3 July 2004, Published online: 12 October 2004PACS: 85.70.Ge Ferrite and garnet devices - 75.30.Ds Spin waves - 76.50. + g Ferromagnetic, antiferromagnetic, and ferrimagnetic resonances; spin-wave resonance     

Vanishing magnetic interactions in ferromagnetic thin films

We have used element-specific hysteresis measurements, based on the x-ray magnetic circular dichroism technique, to investigate magnetic trilayer structures composed of Fe and Ni layers. Within a critical regime we have discovered a class of structures in which the exchange interaction, the mechanism responsible for the macroscopic magnetism, can become vanishingly small. The experimental observations are supported by first principles theory and are explained as arising from a cancellation of several competing magnetic interactions. Hence, we have discovered a system with a novel exchange interaction between magnetic layers in direct contact that replaces the conventional exchange interaction in ferromagnets.