Magnetic Properties Of Thin Films Research Articles

Microstructure and Magnetic Properties of CoFeHfO Rich Nanocrystalline Thin Films Application for High Frequency

Nanocrystalline CoFeHfO thin films have been fabricated by RF sputtering method. Co52Fe23Hf10O15 thin film is observed, exhibit good magnetic properties with magnetic coercivity (Hc) of 0.18 Oe; anisotropy fild (Hk) of 49 Oe; saturation magnetization (4лMs) of 21 kG, and electrical resistivity (ρ) of 300 01cm. The frequency response of permeability of the film is excellent. The effect of microstructure on the electrical and magnetic properties of thin film was studied using X-ray diffraction (XRD) analysis and conventional transmission electron microscopy (TEM). The results showed that excellent soft magnetic properties were associated with granular nannoscale grains of α-CoFe and α-Co(Fe) phases.

Mössbauer spectroscopy and magnetic properties in thin films of Fe xNi 100− x electroplated on silicon (1 0 0)

Fe x Ni 100− x thin films were produced by galvanostatic electrodeposition on Si (1 0 0), nominal thickness 2800 nm, and x ranging 7–20. The crystalline structure of the sample was determined by X-ray diffraction (XRD). The magnetic properties were investigated by vibration sample magnetometry (VSM) and room temperature 57Fe Mössbauer spectroscopy. Conversion Electron Mössbauer spectroscopy (CEMS) in both film surfaces for the thick self-supported films showed that the magnetic moment direction is in the plane and conventional transmission (MS) that the directions are out of the plane films. The results were interpreted assuming a three-layer model where the external layer has in-plane magnetization and the internal one, out of plane magnetization.

Transition-metal silicides as materials for magnet-semiconductor heterostructures

The injection of a spin-polarized current into a semiconductor, one of the key requirements for spintronics, poses the challenge for computational materials science to possibly screen suitable materials. In a number of theoretical investigations, we have put forward magnetic intermetallic compounds grown epitaxially on Si as promising candidates. We employed density functional theory calculations with the GGA-PBE exchange-correlation functional and the full-potential augmented plane wave plus local orbital (FP-APW+lo) method, as implemented in the WIEN2k package. In the spirit of computational materials science, we investigated the stability and magnetic properties of thin films of the Heusler alloy Co2MnSi, as well as of binary late transition metal monosilicides, in contact with the Si surface. For the Heusler alloy Co2MnSi, we could show that the (001) surface retains the half-metallic character of the bulk if a fully Mn-terminated surface is prepared. At interfaces with Si, a finite density of states at the Fermi energy was found for both spin channels, but the half-metallic behavior recovers only a few layers away from the interface. For the monosilicides of the late 3d-transition metals (Mn, Fe, Co, Ni), we predict a CsCl-like structure that has not yet been observed as bulk compound but may be stabilized epitaxially on Si(001). For very thin films of CoSi and MnSi grown in this structure, our calculations find a ferromagnetic ground state. Recently, we identified the atomic structure of MnSi films on Si(111) which is close to the natural crystal structure of bulk MnSi (B20), and also shows large magnetic moments of the Mn atoms at the surface and interface. All MnSi films have a high degree of spin polarization (between 30% and 50%, depending on film thickness) at the Fermi level, and are thus promising materials for fabricating electrical contacts for spin injection into Si.

Relationship between magnetic and structural properties of Ni thin films onGaAs(100)and bulk bcc Ni: First-principles calculations

Recent experimental investigation of electronic and magnetic properties of thin films of bcc Ni grown on a $\mathrm{GaAs}(001)$ substrate allowed to extrapolate towards the magnetic properties of normally unstable bulk bcc Ni metal. Using first principles calculations, we find that due to the lattice mismatch Ni films on $\mathrm{GaAs}(001)$ are under tension and the resulting interlayer relaxation is at about 2.5%. The comparison of the calculated magnetic properties, including the effective interatomic Heisenberg exchange constants derived within the Oguchi-Lichtenstein formalism, for distorted and pure bcc phases of Ni allow to draw a conclusion about the relevance of the experimentally extrapolated properties of pure bcc Ni. We show that a lattice distortion does not alter the values of the magnetic moments significantly, but only moderately influences the effective magnetic exchange interactions as compared to undistorted bulk. We advocate, however, that the experimentally estimated value of the bulk cubic magnetic anisotropy should be taken with precaution, since the omitted contribution due to shear strain may be significant. In addition we discuss the possible existence of weak itinerant ferromagnetism in bcc Ni films prepared under compression.

Electronic and magnetic properties of thin films probed by Auger photoelectron coincidence spectroscopy (APECS)

The recently discovered capabilities of Auger-photoelectron coincidence spectroscopy (APECS), i.e., the emission depth selectivity and the final spin state selectivity, are reviewed and discussed as a tool for the study of complex systems like magnetic thin films and multilayers. After a brief overview of these recent findings and a description of a clear experimental evidence for a dichroic effect in angle resolved (DEAR) APECS, results of coincidence Auger line shape applied to Co film on Cu(0 0 1), are presented. The geometrical configurations used, achieved by means of the high degree of freedom available in the experimental apparatus, are discussed in detail, as well as all the possible combinations that can provide a spin final state selectivity are presented. Due to the very high statistics achieved in the measurement, some finer details can be resolved at energies corresponding to transitions involving electrons from the top and the bottom of the valence band, when comparing singlet versus triplet contributions. As a first attempt and in the simplest approach, the observed dichroism can be explained by appropriate convolutions of the majority and minority densities of states, possibly corrected by a Cini–Sawatzky model for taking into account spin dependent correlation effects.

Preparation and magnetic properties of thin films containing mixtures of superparamagnetic nanocrystals encapsulated in amorphous metal oxides

Nanocomposite thin films consisting of 1:1 mixtures of pre-formed CoFe 2O 4 and γ-Fe 2O 3 nanocrystals (NCs) encapsulated in amorphous aluminum oxide or titanium oxide have been prepared. The nanocrystals were prepared by the thermolysis of iron(III) acetylacetonate and cobalt(II) acetylacetonate in the presence of surfactants. The obtained NCs were codissolved in hexane solutions of either Al(OBu) 2(EtOacac) or Ti(O i Pr) 2(acac) 2 and spin cast as thin films. Upon UV photolysis, the organic ligand was ejected from the film as volatile photoproducts, yielding amorphous metal oxide matrices which contain encapsulated nanocrystals. Zero-field cooled magnetization measurements confirm the presence of both nanocrystals, and show the presence of interparticle interactions.

Tailoring of magnetic anisotropy in amorphous and nanocrystalline soft magnetic alloys using swift heavy ions

Amorphous films of Fe 0.85N 0.15 and Fe 73.9Cu 0.9Nb 3.1Si 13.2B 8.9 have been prepared by using ion-beam sputtering. Magneto-optic Kerr effect (MOKE) and Mössbauer measurement shows that the FeN film has a perpendicular magnetic anisotropy while the finemet film has a uniaxial in-plane anisotropy. The anisotropy in as-deposited state may be attributed to some quenched-in stresses present in the film during deposition. Films have been irradiated with Ag and Au ions of different energies. In both the films, irradiation results in gradual removal of anisotropy and a decrease in coercivity, which may be attributed to relaxation of internal stresses. This demonstrates that swift heavy ions can be used for controlled modification of magnetic properties of thin films.

Thin film stress measurement by instrumented optical fibre displacement sensor

Residual stress can adversely affect the mechanical, electronic, optical and magnetic properties of thin films. This work describes a simple stress measurement instrument based on the bending beam method together with a sensitive non-contact fibre optical displacement sensor. The fibre optical displacement sensor is interfaced to a computer and a Labview programme enables film stress to be determined from changes in the radius of curvature of the film–substrate system. The stress measurement instrument was tested for two different kinds of thin film, hard amorphous carbon nitride (CN) and soft copper (Cu) films on silicon substrates deposited by RF magnetron sputtering. Residual stress developed in 500 nm thick CN thin films deposited at substrate temperatures in the range 50–550 °C was examined and it was found that stress in CN films decreased from 0.83 to 0.44 GPa compressive with increase of substrate temperature. Residual stress was found to be tensile (121 MPa) for Cu films of thickness 1500 nm deposited at room temperature.

FMR study of thin films of Co2Cr0.6Fe0.4Al and Co2MnSi Heusler alloys

The method of ferromagnetic resonance (FMR) was used to study magnetic properties of thin films of half-metallic ferromagnetic Heusler alloys Co2Cr0.6Fe0.4Al and Co2MnSi depending on the film thickness and the presence or absence of a vanadium buffer layer. It is shown that the FMR method is a highly efficient technique for studying nanoscale magnetic properties of thin films, especially for the investigation of their magnetic inhomogeneities and anisotropy. Samples of Co2Cr0.6Fe0.4Al and Co2MnSi were prepared by magnetron-sputtering deposition on substrates of single-crystal silicon dioxide (SiO2) with an orientation (100). It has been shown that the magnetic properties of thin Co2Cr0.6Fe0.4Al films strongly depend on both the film thickness (25 or 100 nm) and the presence of an intermediate vanadium layer (50 nm). Well-resolved spin-wave modes were observed in the sample 100 nm thick without a vanadium buffer layer, which made it possible to determine the parameter of spin stiffness D for this ferromagnet. Two series of thin films of Co2MnSi have also been studied, which were prepared on a buffer layer of vanadium (42 nm thick): (1) with various thicknesses (4–100 nm) and a fixed annealing temperature (450°C) and (2) with a fixed thickness (80 nm) and various annealing temperatures (425–550°C). It has been shown that in the series of Co2MnSi films with a variable thickness (4–100 nm) the greatest value of magnetization is reached for a film with a thickness of 61 nm. The investigations of the other series of films, which were annealed at various temperatures, show that to achieve both a greater magnetization and a better structural homogeneity, annealing at temperatures T ≥ 450°C is required. In addition, low-intensity spin-waves were observed in some samples with thicknesses of 100 and 61 nm, which made it possible to estimate the spin-stiffness parameter D for the Co2MnSi Heusler alloy as well.

Generalized theory and application of Stokes parameter measurements made with a single photoelastic modulator

We report in this paper a generalized theory that describes the interaction between a monochromatic light beam and an optical system that includes one photoelastic modulator, one analyzer, and one photodetector. Based on the theory, a detailed four-step procedure is presented, which allows a precise measurement of the four Stokes parameters. An analysis of the systematic and random errors arising from the four-step measurements is also given as well as a calibration procedure that involves the use of a general retardation plate. As a practical application the procedure is used to analyze the magneto-optical properties of magnetic thin films grown on GaAs(001) substrates.

Surface and thin film studies with polarized low energy muons

Muons with 100% spin polarization and whose energy can be continuously varied in the keV range provide a novel extension of the muon spin rotation/relaxation technique and can be used for surface and thin film studies. They allow depth dependent studies on a nm scale of the magnetic properties of thin films and multilayered structures in the range from about 1 nm to a few 100 nm. After a short introduction about the use of muons as thin film microprobes we summarize some representative examples of applications such as the measurement of magnetic field profiles near the surface of superconductors, the absolute determination of the magnetic penetration depth, and the detection of the oscillating conduction electron spin polarization in multilayered structures.

CoFeHfO 박막의 자기적 특성

Amorphous alloys of Co-rich magnetic amorphous films are well known as thpical soft magnetic alloys. They are used for many kinds of electric and electronic parts such as magnetic recording heads, transformers and inductors. CoFeHfO thin films were prepared by RF magnetron reactive sputtering. The films were deposited onto Si(100) substrates with a power of 300 W at room temperature. The reactive gas was introduced up to 10% (/(Ar + )) during deposition, and the thin film exhibit excellent soft magnetic properties : saturation magnetization () of 19kG, magnetic coercivity () of 0.37 Oe, anisotropy field () of 48.62 Oe, and an electrical property is also shown to be as high as 300 . It is assumed that the good soft magnetic properties of thin film results from high electrical resistivity and large anisotropy field.

High-field cantilever magnetometry as a tool for the determination of the magnetocrystalline anisotropy of single crystals

Cantilever torque magnetometry is utilized widely in physics and material science for the determination of magnetic properties of thin films and semiconductors. Here, we report on its first application in rock magnetism, namely the determination of K 1 and K 2 of single crystal octahedra of natural magnetite. The design of cantilever magnetometers allows optimization for the specific research question at hand. For the present study, a cantilever magnetometer was used that enables measurement of samples with a volume up to 64 mm 3. It can be inserted into an electromagnet with a maximum field of 2 T. The cantilever spring is suitable for torque values ranging from 7.5 × 10 − 7 N·m to 5 × 10 − 6 N·m. The torque is detected capacitively; the measured capacitance is converted into torque by using a calibrated feedback coil. The magnetometer allows in-situ rotation of the sample in both directions and is, therefore, also suitable to analyze rotational hysteresis effects. The evaluation of the magnetite anisotropy constants involved Fourier analysis of the torque signal on the magnetite crystals' (001) and (110) planes. The absolute anisotropy constant has been computed using the extrapolation-to-infinite-field method. The value of K 1 at room temperature is determined at − 1.28 × 10 4 [J m − 3] (± 0.13, i.e. 10%) and that of K 2 at − 2.8 × 10 3 [J m − 3] (± 0.1, i.e. 2%). These values concur with earlier determinations that could not provide an instrumental error, in contrast with this work. The cantilever magnetometer performs four times faster than other torque magnetometers used for rock magnetic studies. This makes the instrument also suitable for magnetic fabric analysis.

The effect of Ge substitution in Ni 2 MnGa 1– x Ge x Heusler alloys and films

We present the results on the effect of adding Ge on the magnetic properties of Ni2MnGa1–x Gex (0 < x < 0.4) alloys and thin films deposited by flash-evaporation from the powdered alloys. It is found that the annealed alloys are single phase with L21 ordering (cubic lattice constant a ≃ 0.581 nm). The Ge addition causes a drastic decrease in the martensitic transformation temperature from T M = 200 K (x = 0) to T M = 50 K (x = 0.4) with almost no effect on the Curie temperature T C ≃ 380 K and magnetization M S (0) ≃ 450–500 G. The magnetic properties of thin films strongly depend on ordering. The ordered films have similar L21 (or B2) ordering and exhibit the magnetic properties similar to the properties of corresponding bulk alloys. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ion beam sputtered thin films of finemet alloy for soft magnetic applications

Amorphous films of finemet composition (Fe73.9Cu0.9Nb3.1Si13.2B8.9) have been prepared using ion-beam sputtering of a target made out of amorphous ribbons of same composition. Effect of film thickness on the magnetic anisotropy as well as coercivity has been studied. It is suggested that domain wall pinning at surface irregularities as well as random stresses may significantly affect the coercivity. Nanocrystallisation of the film by controlled thermal annealing results in significant change in coercivity, which can be understood in terms of the random anisotropy model. Irradiation of amorphous film by 120MeV Ag+ ions results in a significant decrease in coercivity. This may be correlated with improvement in the surface smoothness and possible relaxation of random stresses. Present results show that swift heavy ion irradiation (SHI) can be effectively used as a tool to improve the soft magnetic properties of thin films.

Domain patterning and thermodynamic properties in magnetic films with perpendicular anisotropy

We have studied the magnetic domain patterns and the thermodynamical properties of magnetic thin films with perpendicular anisotropy. The temperature dependence of the domain pattern, specific heat, susceptibility, and spatial correlation function were calculated based on the Monte Carlo method. A modified Ising Hamiltonian including the long-range dipole-dipole interaction was used. An order parameter based only on the magnetic domain symmetry was defined allowing the investigation of possible relationships between different patterns and thermodynamical properties on the phase transition. The proposed approach can be potentially useful for experimental works where the magnetic domain pattern analysis on any phase transition (magnetic, structural, etc.) is required.

Near-surface magnetic properties of CoFeAlO thin films

We present here, the results of a thorough study of the surface and magnetic properties of as-deposited and annealed Co–Fe–Al–O thin films using the magneto-optical Kerr effect technique. An increase in magnetic anisotropy was found in the near-surface region of the film, which is ascribed to the microstructural change occurring in this region. It is found that the partial pressure of oxygen caused considerable changes in the transverse Kerr effect spectra and hence the magnetic properties of the thin films. The step-like magnetization behavior was observed at a light wavelength of 310 nm while it disappeared for higher wavelengths of light. The step-like magnetization phenomenon is due to the magnetic wall displacement process of each fracturized domain in the surface region.

Applied muon science: novel perspectives in nano-science

Starting from an intense surface muon beam a tertiary beam of muons with 100% spin polarization and whose energy can be continuously tuned in the keV range was recently developed at PSI. This allows to vary the implantation depth in thin samples in the interval from ∼ 1 nm to a few hundred nm. By means of muon spin rotation/relaxation techniques these low energy particles have been used as novel local probes to study magnetic properties of thin films, near surface regions and multilayered structures.

Structural and compositional analysis of transition-metal-doped ZnO and GaN PLD thin films

We have studied the structural and magnetic properties of thin films of ZnO and GaN semiconductors doped with magnetic and non-magnetic transition-metals. The films were prepared on sapphire substrates by pulsed laser deposition from doped ceramic targets. Room temperature ferromagnetism was observed in ZnO (doped with Sc, Ti, V, Fe, Co or Ni) and in Mn-doped GaN films. In both cases, single crystal epitaxial growth was observed. The higher dopant:Zn ratio observed in the films is attributed to the preferential sputtering of Zn by energetic ions in the laser ablation plasma plume.

A new broad-band method for magnetic thin-film characterization in the microwave range

A new method for magnetic thin-film characterization is presented. New microwave electronic technology challenges require integration of many passive components on chips. Among them, isolators and circulators are nonreciprocal passive devices which contain magnetic materials. The use of thin magnetic films in place of bulk materials seems to be a solution to integrate these components on chips. Hence, it is important to know the magnetic properties of thin films in the microwave range. An isolator is obtained by locating the thin magnetic film in a coplanar line; however, it is often difficult to measure the constitutive parameters of the film before the end of its production. The method described allows in situ measurement of two parameters of the film permeability tensor.