Papers by Keyword: Magnetic Anisotropy

Abstract: The solid-state reaction between epitaxial hcp-Co (110) and fcc-Co (001) thin films and Pd layers was investigated at annealing temperatures between 250 and 650 °C using X-ray diffraction and magnetic measurements. No significant intermixing of the layers occurs at annealing temperatures below 400 °C. For the atomic composition 1Co:1Pd after annealing at 450 °C the disordered solid solution fcc-Co_xPd_1-x is formed on the Pd/hcp-Co (110) and Pd/fcc-Co (001) interfaces. Epitaxial relationships CoPd (110)〈-111〉 || MgO(001)〈100〉 and CoPd (001)〈100〉 || MgO(001)〈100〉 between the nucleated disordered phase CoPd and the substrate MgO(001) were determined for Pd/hcp-Co (110) and Pd/fcc-Co (001) bilayers, respectively. The first magnetocrystalline anisotropy constant of the disordered CoPd phase ​​K₁^CoPd = - (1.8 ± 0.4)·10⁴ J/m³ for the (110) and (001) orientations was obtained.

Abstract: Thin films of Co-Hf (≈ 86-14 % at.) were grown over Si micro-cantilevers using a glancing-angle deposition technique. A controlled easy direction of magnetisation (anisotropy field μ_oH_k ≈ 0.1 T) in the longitudinal or in the transverse direction of the micro-cantilevers was generated. The mechanical properties of the films under the action of a magnetic field were opposite depending on the magnetisation’s easy direction: i) their deflection was either zero or the maximum value depending on the direction of the applied magnetic field with respect to the parallel or transverse easy direction of magnetisation; ii) the shift in the resonance frequency under a longitudinal or transverse magnetic field was also different depending on the longitudinal or transverse easy direction of magnetisation. The use of these coated devices with micromagnet-like films for sensors and transducers is discussed.

Abstract: Ferromagnetic iron nanoellipsoids were prepared by the hydrogen reduction of ellipsoidal hematite nanoarchitectures. These magnetic nanoscale particles displayed a microstructure that showed clear similarities to the magnetosome chains of the magnetotactic bacteria. Specifically, such nanoellipsoids are formed by single-domain nanocrystals assembled into double chains sharing the same crystallographic orientation. In the present contribution, the magnetic properties of the Fe nanoellipsoids were explained considering the chain of spheres model of Jacobs and Bean, and thermal effects.

Abstract: A practical way to manipulate the magnetic anisotropy of magnetostrictive FeGa thin films grown on flexible polyethylene terephthalate (PET) substrates is introduced in this study. The effect of film thickness on magnetic properties and magnetostriction constant of polycrystalline FeGa thin films was investigated. The anisotropy field H_k of flexible FeGa films, i.e., the saturation field determined by fitting the hysteresis curves measured along the hard axis, was enhanced with increasing the tensile strain applied along the easy axis of the thin films, but this enhancement via strain became unconspicuous with increasing the thickness of FeGa films. In order to study the magnetic sensitivity of thin films responding to the external stress, we applied different strains on these films and measure the corresponding anisotropy field. Moreover, the effective magnetostriction constant of FeGa films was calculated from the changes of both anisotropy field and external strain based on the Villari effect. A Neel’s phenomenological model was developed to illustrate that the effective anisotropy field of FeGa thin films was contributed from both the constant volume term and the inverse thickness dependent surface term. Therefore, the magnetic properties for the volume and surface of FeGa thin films were different, which has been verified in this work by using vibrating sample magnetometer (VSM) and magneto-optic Kerr effect (MOKE) system. The anisotropy field contributed by the surface of FeGa film and obtained by MOKE is smaller than that contributed by the film volume and measured by VSM. We ascribed the difference in H_k to the relaxation of the effective strain applied on the films with increasing the thickness of films.

Abstract: Nickel films are grown by radio frequency magnetron sputtering on Corning glass, polyimide foils and on the native oxide of Si (100) wafers at low (1x10^-3 mbar) and relatively high (2.5x10^-2 mbar) Argon pressure at 100 °C. The base pressure of the high vacuum chamber is 1x10^-7 mbar. X-ray diffraction experiments are performed to reveal the different texture of various Ni films. Magneto-optical Kerr effect hysteresis loops and magnetic force microscopy images show correlation between Argon pressure, texture and magnetic anisotropy of the films. The results are discussed with respect to relevant measurements of Ni/NiO magnetic multilayers prepared under similar experimental conditions.

Abstract: We have evaporated series of Co thin films under vacuum onto silicon and glass substrates at a perpendicular and oblique incidence. The thickness of the magnetic layer ranges from 20 to 400 nm. The static magnetic properties have been performed by means of magnetic force microscopy (M.F.M.) and Alternating Gradient Field Magnetometer (A.G.F.M.) techniques. The influence of the magnetic layer thickness and the deposition angle are studied. As results, it is found a decrease of the coercive field from 250 Oe, for t = 20 nm, to 95 Oe, for t = 400 nm. These H_c values for obliquely evaporated cobalt films are larger than those measured for cobalt films evaporated at normal incidence, found to be equal to a few Oe. It is also found a decrease of the anisotropy field, from 1.6 kOe for the 20 nm Co thick film to 0.95 kOe for the 200 nm Co thick film. Furthermore, an increase of these fields with the increase of the deposition angle is found, as well. The easy axis of the saturation magnetization lies in the film plane, irrespective of the substrate nature. These results, and others, are presented and discussed.

Abstract: Phase composition, crystal structure and magnetic properties of ordering FePd and Fe₅₀Pd_50-xPt_x (х = 1-10 atomic %) alloy films were studied. Spectral dependencies of Faraday rotation and optical absorption were measured. We studied how thermal treatment affects crystal structure, magnetization and coercive force in ordered alloys and how the degree of atomic order affects the value of perpendicular magnetic anisotropy. It was shown that near equiatomic ordered FePd and Fe₅₀Pd_50-xPt_x (х = 1-10 at. %) alloy films can be used as medium for magnetic and thermo-magnetic data recording.

Abstract: Phase transitions between incommensurate spin states in ferroelectromagnet TbMnO₃ in magnetic field along the modulation vector are phenomenologically analyzed. It is shown that the competition between different terms of the fourth order in magnetic anisotropy energy is a reason of the reorientation of spin-cycloid plane and electric polarization by 90⁰ (polarization flop). Calculated phase diagram is in a good agreement with experimental data.

Abstract: Magnetic anisotropy of thin films and nanodisk arrays made of cobalt has been studied by the magneto-optical anisometry with modulated field. The improved method of magnetic anisotropy field measurements in thin films has been proposed. This method has been used for cobalt nanodisk arrays in order to investigate anisotropy of magnetization reversal processes due to dipole-dipole interaction between nanodisks.

Abstract: Abstract. With the use of magneto-optical Faraday effect effective field of perpendicular magnetic anisotropy of iron garnet films is measured in vacuum and in the atmosphere of water vapor. It is established that a decrease of the mentioned field takes place due to adsorption of the water molecules by 20% in comparison with the value of field in vacuum. This result is in accordance with the conclusion reached on the base of investigation of influence of water molecules adsorption on domain structure of iron garnet films earlier.