Anisotropy of thin ferromagnetic films

A model is proposed and checked experimentally to describe a direct relationship between the anisotropy of thin ferromagnetic films and the texture of a low-symmetry magnetically ordered phase of CoFe alloy which has a monoclinic unit cell. The measured distortions of the initial cubic cell are an order of magnitude greater than the magnetostriction constants of the solid sample. An analysis is made of a system for the formation of anisotropic stresses in the plane of the film in which this effect is attributed to the magnetic texture. A suitable method is developed for making diffraction measurements and analyzing the experimental data. Pis’ma Zh. Tekh. Fiz. 24, 51–56 (October 12, 1998)     

Saturation magnetization in ferromagnetic thin films

The present status of the theory of saturation magnetization of ferromagnetic thin films is reviewed. The extensions of the Heisenberg trace method and the spin-wave method to the case of ferromagnetic thin films is fully discussed together with a comparison of the theoretical results with experimental data. The effect of anisotropic magnetic fields on magnetization and Curie temperature is presented, and the dependence of the magnetization and Curie temperature on film thickness is studied. Very recent progress and new results of the theory are stressed. The application of the Green function method to ferromagnetic thin films is also examined.     

Magnetooptical investigations on thin ferromagnetic films

Various applications of the Faraday and Kerr effects for the investigation of domain structures and reversal mechanisms in thin ferromagnetic films are reviewed. Different optical arrangements for the observation of domains are described and compared. Using magnetooptic microscopy domains and wall structures can be observed with a resolution of 1 μm. Magnetization structures give rise to diffraction phenomena, which are revealed as Fresnel fringes, Fraunhofer patterns, and dark field pictures. Applications of these phenomena and the consequences for the resolution of magneto-optic microscopy are discussed. Various kinds of reversal processes by wall motion or rotation, respectively, can be distinguished from each other by measuring the light intensity in two settings of the analyzer and by a dark field method. These reversal mechanisms can be identified even in case of fast switching when direct observations are not possible. Since the applications of magnetooptics are not restricted by any temperature limit, they are especially suited for the investigation of temperature dependent phenomena, e.g., the Barkhausen effect and the magnetic aftereffect. A picture of a domain structure in a gadolinium film at 80°K is shown.     

Static wall coercive force in ferromagnetic thin films

The static wall coercive force of thin ferromagnetic films has been calculated from a model of conservative wall energy. The spatial dependence of the wall energy γwis assumed to be given by the mean value of the local anisotropy energy, averaged over a coupling volume of the wall. The result of the calculation shows thatH_{w} propto frac{S}{M_{s}} (frac{D}{W})^{1/2} frac{1}{L}where the structure constantSincludes the local anisotropy,Dis the mean diameter of a region with constant anisotropy (for instance crystallites),Wis the wall width; andLis the coupling length parallel to the wall.     

Measurements and modeling of linear and nonlinear effects in striplines

We present measurements of surface impedanceZ _S as a function of frequency, temperature, and rf magnetic field for high-quality epitaxial YBa₂Cu₃O_7–x thin films using a striplineresonator technique that measures theQ of the resonator vs. input power. The results have been modeled using Ginzburg-Landau theory at moderate fields, and the Bean critical state model at high fields. Good agreement has been obtained between the model and the measurements. We also discuss the current distributions in the stripline for both low power whenZ _S is linear and high power whenZ _S is nonlinear.     

Characterization of low losses in optical thin films and materials

Residual absorption in optical coatings and materials is directly measured by means of the laser-induced deflection (LID) technique. For transmissive coatings a measurement strategy is introduced that allows for the separation of different absorptions of the investigated sample (bulk, coating, surface) by use of only one sample. Laser irradiation yields absorption values between 2 x 10(-3) and 2.9 x 10(-2) for antireflecting and highly reflecting (HR) coatings at 193 nm and 30.6 x 10(-6) for a HR mirror at 527 nm. Use of laser-induced fluorescence at 193 nm excitation reveals trivalent cerium and prasodymium and hydrocarbons in different single layers and coatings. In addition to correlation with absorption data, the influence of a high fluorescence quantum yield on the absorption measurement is discussed.     

GHz高磁导率铁磁薄膜研究进展

主要介绍了微波(GHz)频率下,高磁导率铁磁性薄膜近年来的最新研究进展。对于制备在柔性基片上的铁磁薄膜,重点介绍了Fe基、Co基合金薄膜,并分析了各成分对薄膜的影响;纳米晶薄膜的重点集中在Fe—N及FeXN系薄膜上,介绍了各类FeN相在薄膜中所起的作用;对于T—M—O系纳米磁性颗粒膜,分析了磁性颗粒膜的微波高磁导率机理。同时提出了目前探索GHz频率下高磁导率磁性薄膜主要面临的问题。     

Synthesis and characterization of ferromagnetic cobalt-doped tin dioxide thin films

Co-doped SnO₂ thin films are grown on sapphire (0001) substrates at 600 °C by the technique of dual-beam pulsed laser deposition. The prepared films show preferred orientation in the [100] direction of the rutile structure of SnO₂. Nonequilibrium film growth process results in doping Co into SnO₂ much above the thermal equilibrium limit. A Film with 3% of Co is ferromagnetic at room temperature with a remanent magnetization of ∼ 26% and a coercivity of ∼ 9.0 mT. As Co doping content x increases, the optical band gap absorption edge (E₀) of the Co-doped SnO₂ thin films initially shows a redshift at low x up to x = 0.12 and then increases at the higher x, which are attributed to the sp-d exchange interactions and alloying effects, respectively.     

Segregation and phase separation in thin films

Surface segregation and phase separation in binary AB systems have been calculated in a slab consisting of atomic planes perpendicular to the free surfaces. For strongly segregating systems, if the average concentration lies in the two phase region of the binary phase diagram, a phase separation from the surfaces develops and two layers of the A-rich phase cover the A-poor central phase in the slab (lamellar structure). Furthermore, there is an enrichment (segregation) of A atoms in the near surface layers of the upper phase. For weakly segregating systems there exists a critical concentration C_h. If T > T_h (T_h is the temperature on the miscibility gap at C_h), a similar phase separation and segregation has been observed as above. However, for T < T_h, two different phases can be in equilibrium in a columnar structure. The concentrations in their central layers, if the slab is thick enough, correspond to the compositions of the miscibility gap at the given temperature. At the same time, there is a strong segregation of A atoms in the A-poor phase, while, due to the stronger separation tendency, the minority B atoms will ‘separate’ at the surface, leading to a desegregation of A atoms in the A-rich phase.     

Magnetic phase transition in thin films

The theory of phase transitions in magnetic systems with surfaces is reviewed. Results of the phenomenological Landau-Ginzburg theory as well the scaling theory are briefly presented and compared with those obtained for particular microscopic models. Possibilities of special kinds of magnetic phase transitions in systems with surfaces are also presented.     

Thickness dependence of the polar Kerr effect in thin ferromagnetic films

Using a general scattering matrix approach in the theoretical analysis the polar Kerr rotation is shown to have a marked dependence on sample thickness when the thickness is less than 60 nm. The polar Kerr rotation is calculated for thin films of iron and cobalt for normal incidence in the wavelength range 400–1400 nm for both unbloomed and bloomed specimens.     

Magnetic properties of thin ferromagnetic films in relation to their structure

The influence of film structure on magnetic properties is primarily due to the creation of spatially fluctuating local anisotropies which make the magnetization direction inhomogeneous. The deviation from homogeneous magnetization of domains, the so-called ripple, influences a great number of static, quasistatic and dynamic effects via the intrinsic demagnetizing field. The ripple theory is expressed in terms of only one phenomenological constant, the structure constant S, which covers completely the influence of the film structure on the deviations of real thin film behaviour from that of ideal single domains.     

Some remarks on the surface inhomogeneity model in thin ferromagnetic films

Collinear ferromagnetic spin ordering in a thin film with pinned surface spins is shown to be stable only for certain orientations of the magnetisation vector. Also, the magnon potential is shown to extend outward from the film surface; according to whether the surface spins are pinned more strongly or less strongly than the internal spins, the potential becomes infinite at a distance outward from the surface smaller or larger than one lattice constant.     

Magnetic imaging in thin magnetic films by local spectrometer of ferromagnetic resonance

The automatized scanning spectrometer of ferromagnetic resonance has been designed for measuring a distribution of in-plane magnetic anisotropy, effective saturation magnetization, coercivity, and other performances across the area of thin magnetic films (TMFs) in a monodomain state. The spectrometer is supplied with a set of plug-in measuring heads overlapping frequency band 0.1 /spl divide/ 6.0 GHz. The degree of locality of measurements in the range 0.3 /spl divide/ 2.5 mm is defined by the size of the measuring hole in the microstrip resonator built in the head. The signal-to-noise ratio of the heads is not less than 10 for permalloy film of 100-/spl Aring/ thickness when the locality of measurements is about 1 mm, and it can be increased considerably in the signal accumulation mode. Magnetic imaging is demonstrated with an example of purposely-stressed TMFs.     

Atomic layer deposition of ferromagnetic cobalt doped titanium oxide thin films

TiO₂ thin films doped or mixed with cobalt oxide were grown by atomic layer deposition using titanium tetramethoxide and cobalt(III)acetylacetonate as metal precursors. The films could be deposited using both O₃ and H₂O as oxygen precursors. The films grown using water exhibited considerably smoother surface than those grown with ozone. The TiO₂:Co films with Co/(Co + Ti) cation ratio ranging from 0.01 to 0.30 were crystallized by annealing at 650 °C, possessing mixed phase composition comprising rutile and anatase and, additionally, CoTiO₃ or CoTi₂O₅. The annealed films demonstrated magnetic response expressed by magnetization curves with certain hysteresis and coercive fields.     

The phase transition of djurleite thin films

Thin films of djurleite have been examined by TED in order to study the phase transition at 86° C. The samples were heated during observation in the electron microscope. Under these conditions no intermediate phase was found, but we have found two different orientations of the djurleite supercell with respect to the high chalcocite cell. The transformation matrix was determined.     

Band model approach for the magnetic stiffness within ferromagnetic thin films

The magnetic stiffness within ferromagnetic thin films, considered as a tendency of the film to be homogeneous with respect to the distribution of magnetization directions, is defined on the basis of the domain structure as well as of the spin wave theory. The transversal stiffness parameter in thin films is calculated by means of the band model approach within a Hartree-Fock type of approximation. This parameter depends on the film thickness and, what is particularly interesting, on the surface effects.     

High rate magnetron sputtering of ferromagnetic SmCo, Fe and CoCr thin films

Ferromagnetic thin films have been sputtered from a modified conventional magnetron cathode (3" diameter). The targets (5 to 6 mm thick) were stainless steel, demagnetized SmCo5and CoCr(15-18 at% Cr). The deposition rate was 6 nm/s at a power density of 15 W/cm². Increasing the power rates up to 12 nm/s could be achieved. The saturation magnetization ranged from 0.4 to 1,5 Tesla. The films sputtered from stainless steel had a magnetization only 30 % smaller than the magnetization of Fe. The coercive force varied from 0.8 to 75 kA/m.     

Thickness-dependent phase transformation in nanoindented germanium thin films

We investigate the mechanical response of 50-600?nm epitaxial Ge films on a Si substrate using nanoindentation with a nominally spherical (R≈4.3?μm) diamond tip. The inelastic deformation mechanism is found to depend critically on the film thickness. Sub-100?nm Ge films deform by pressure-induced phase transformation, whereas thicker films deform only by shear-induced dislocation slip and twinning. Nanoindentation fracture response is similarly dependent on film thickness. Elastic stress modelling shows that differing stress modes vary in their spatial distribution, and consequently the film thickness governs the stress state in the film, in conjunction with the radius of the nanoindenter tip. This opens the prospect of tailoring the contact response of Ge and related materials in thin film form by varying film thickness and indenter radius.