Values Of Magnetic Anisotropy Research Articles

Magnetic Properties of $\gamma$-Fe$_{2}$O$_{3}$ Nanoparticles Precipitated in Alginate Hydrogels

gamma-Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> magnetic nanoparticles ranging in average diameter from 2 to 4 nm were precipitated within an alginate hydrogel and characterized by X-ray diffraction (XRD), Mossbauer spectroscopy, and SQUID magnetometry. Regardless of the initial Fe valence state of the starting chloride salt, Mossbauer spectroscopy confirmed that gamma-Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> was the only phase present. As expected, the nanoparticles exhibited superparamagnetic behavior with the magnetic moments becoming frozen with decreasing temperature as evidenced by a bifurcation in the zero-field-cooled (ZFC) and field-cooled (FC) magnetizations and a hysteresis in the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">Mv</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">vs.</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> curves. The values of effective magnetic anisotropy ( ~ 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">6</sup> ergs/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> ) determined from the differences between the ZFC and FC magnetizations were found to be an order of magnitude larger than the magneto-crystalline anisotropy for bulk gamma -Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> , and are probably the result of surface and particle size dependent effects. Likewise, the nanoparticle size distributions as deduced from the blocking temperature distribution function <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">f</i> ( <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">TB</i> ) based on fits to the difference in the ZFC and FC magnetization curves as well as from fits of the <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">MV</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">vs.</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> curves with a Langevin function in the superparamagnetic regime indicate fairly broad distributions of particle sizes with the particle sizes being comparable to those deduced from XRD measurements. The smaller saturated magnetization values found for these nanoparticles than the bulk value combined with the non-zero slope of the high-field magnetization data suggests that these nanoparticles have a non-negligible surface layer of non-collinear spins surrounding a ferrimagnetically ordered gamma-Fe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> core.

Magnetic anisotropy and resonance frequency of patterned soft magnetic strips

FeTaN thin films of 100nm with in-plane uniaxial anisotropy were fabricated by rf magnetron sputtering and patterned into strips with width varied from 30to500μm along both the easy and hard magnetization axes of the unpatterned films. The values of effective magnetic anisotropy of the patterned films increase as the strip widths decrease. The ferromagnetic resonance frequency showed a corresponding increment from 1.38to2.58GHz as the strip width varied. It indicates that this method is effective to tune the ferromagnetic resonance frequency of magnetic thin films. The resultant permeability spectra were understood according to the well-known Kittel formula where an averaged shape anisotropy arisen from the patterning was taken into account for the strips patterned along the easy axis. For the strips patterned along the hard axis, the increase in resonance frequency in narrower strips is attributed to the strengthened internal domain pinning effect predicted from the domain patterns numerically calculated.

Study of the magnetic properties on Mn and As co-implanted GaAs

The interest on diluted magnetic semiconductor (DMS), like GaMnAs, has increased during the last years due to potential applications, mainly on spintronic device. The magnetic anisotropy and the interacting effects between the magnetic nanostructures are fundamental topics to be studied. In this work we present some results on Mn and As co-implanted GaAs. Samples with three different implantation energies of Mn were prepared, keeping the As implantation energy fixed and the Mn and As dose of 2×10 16 cm −2. Annealing was done using rapid thermal annealing (RTA) at 750 °C for 20 and 50 s. Using a superconducting quantum interference device (SQUID) and magnetic anisotropy values reported in the literature, we have obtained information about nanocluster size distribution. Our studies indicated that the nanocluster size distribution depends on the implantation parameters and the annealing time. Differently from previous studies reported in similar samples, we have observed room-temperature hysteresis in all samples, with coercive field values typical of nanoparticle systems.

Low temperature vacuum annealing study of (Co∕Pd)n magnetic multilayers

The correlation between the magnetic properties and the microstructural and chemical composition modifications of Co∕Pd magnetic multilayers upon annealing in ultrahigh vacuum at 250°C is presented. Magnetic characterization using magnetic sample magnetometer shows the vertical magnetic anisotropy increase and the switching field distribution decrease in the annealed samples. The larger values of magnetic anisotropy in the annealed samples are further shown using the magnetic force microscopy of the ac demagnetized states in the Co∕Pd multilayer films. X-ray diffraction rocking curves show an improvement in the texture and the initial magnetization curve slopes indicate the decreases in defect densities. Overall, vacuum annealing under optimal conditions improves the magnetic properties of Co∕Pd multilayers for applications in ultrahigh density magnetic recording.

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.

A study of the magnetic properties of mixed ferrite nanoparticles in ferrofluids

Magnetic properties of Zn x Co 1− x Fe 2O 4 ( x = 0.3, 0.5 and 0.7) nanoparticles in ferrofluids have been investigated by means of Mössbauer spectroscopy in the temperature range 4.2–300 K. The mean sizes of the particles were 10.2, 7.4 and 5.2 nm, respectively. The transition temperatures to the superparamagnetic state and values of crystal magnetic anisotropy have been evaluated. The transition to the superparamagnetic state was observed at temperatures below the freezing point of the carrier liquid for the 5.2 nm and 7.4 nm particles and above its freezing point for the 10.2 nm particles. A multi-level model is used in the analysis of the Mössbauer spectra and in the calculation of the hyperfine magnetic field.

Langevin dynamic simulations of fast remagnetization processes in ferrofluids with internalmagnetic degrees of freedom

In this paper we present a model which allows numerical studies of ferrofluid dynamicstaking into account the internal magnetic degrees of freedom of the ferrofluid particles. Instandard ferrofluid models the magnetic moment of a ferrofluid particle is supposed to befixed with respect to the particle itself, which corresponds to the limit of an infinitelyhigh single-particle magnetic anisotropy. In contrast to this strongly simplifyingassumption, we take into account that in real ferrofluids the magnetic moments offerrofluid particles are allowed to rotate with respect to the particles themselves. Ourmodel results in a system of equations of motion describing both magnetic andmechanical degrees of freedom, where the ‘magnetic’ equations are coupled withthe ‘mechanical’ equations via (i) the interparticle distances determining themagnetodipolar interaction fields and (ii) orientations of the particle anisotropy axes withrespect to their magnetic moments which define the mechanical torque on theparticle.Using our model we have studied the ferrofluid magnetization dynamics for various particleconcentrations, i.e., for various magnetodipolar interaction strengths. In particular, wepresent numerical results (a) the magnetization relaxation of a ferrofluid after the externalfield is switched off and (b) the frequency dependence of the ferrofluid AC susceptibility.Comparing these results with the corresponding dependences obtained for the rigid dipolesmodel, we demonstrate that for magnetic anisotropy values typical for commonlyused ferrofluid materials (like magnetite) the inclusion of ‘magnetic’ degrees offreedom is qualitatively essential to obtain a correct description of the ferrofluiddynamics.

Anisotropy energy distribution determined by Mössbauer spectroscopy in a metallic glass

The distribution of frozen-in magnetic anisotropy in as-quenched Fe 73.5Si 13.5Cu 1Nb 3B 9 amorphous melt-spun ribbons was studied by Mössbauer effect spectroscopy, using the temperature-dependent magnetoelastic effect produced on the metallic glass by 1 μm Al coatings. Al coatings were deposited by RF sputtering at T≈350 K on both sides of the amorphous ribbons. Estimated magnetic anisotropy values were below 1 kJ/m 3, with preeminence of anisotropy energy densities lower than 300 J/m 3.

Spin-wave spectrum of a magnonic crystal with an isolated defect

Real magnonic crystals—periodic magnetic media for spin-wave (magnon) propagation—may contain some defects. We report theoretical spin-wave spectra of a one-dimensional magnonic crystal with an isolated defect. The latter is modeled by insertion of an additional layer with thickness and magnetic anisotropy values different from those of the magnonic crystal constituent layers. The defect layer leads to appearance of several localized defect modes within the magnonic band gaps. The frequency and the number of the defect modes may be controlled by varying parameters of the constituent layers of the magnonic crystal.

Ripening during magnetite nanoparticle synthesis: Resulting interfacial defects and magnetic properties

The structure and magnetic properties of magnetite (Fe3O4) nanoparticles synthesized by a solvothermal processing route are investigated. The nanoparticles are grown from the single organometallic precursor Fe(III) acetylacetonate in trioctylamine (TOA) solvent at 260°C, with and without the addition of heptanoic acid (HA) as a stabilizing agent. From the temporal particle size distributions, x-ray-diffraction patterns, high-resolution transmission electron microscope tilt series experiments, and superconducting quantum interference device magnetometry, we demonstrate that HA, a strong Lewis acid stabilizing agent, slows growth processes during ripening thus reducing the formation of interfacial defects, which we observe in the TOA-only synthesis. Nanoparticles grown with HA remain single crystalline for long growth times (up to 24h), show a focused particle size distribution for intermediate growth times (3h), and possess a higher magnetic anisotropy (15.8×104J∕m3) than particles grown without the additional stabilizing agent. The reduced magnetic anisotropy value for the magnetite nanoparticles grown in TOA only (1.29×104J∕m3) is attributed to polycrystallinity induced by the uncontrolled ripening process. This work may have significance for contrast enhancement in magnetic resonance imaging.

LC Vision: The Application to Magnetic Material Domains Investigations

ABSTRACT The information about local changes of H-field detecting domain structures or magnetic inhomogeneities on the surface of magnetic materials is important for science and high technology. It may be obtained with thin layers (≈ 1 μm) of oriented NLCs and polarizing microscope. In the paper we summarize the universal application of LC vision to magnetic domains investigation in mineralogy, metallography and optical technology. In mineralogy the objects of investigation were the sections of rocks with inclusions of ferromagnetic minerals. On the surface of materials applied for storage devices such as (YLa)3Fe5O12 thin films being grown on the substrate of Gd3Ga5O12 the labyrinthical, striped and cylindrical domain structures were observed in the case when the vector of H-field is parallel to optical polarization vector. The domains on the surface of thin amorphous Co based alloy ribbons were investigated using NLC materials with improved value of magnetic anisotropy. The NLC technique results were compared with the results obtained with magnetic emulsion technique.

Magnetic and microstructural properties of the BaFe (12−(4/3)x)Sn xO 19 ceramic system

The magnetic and microstructural properties of the M-type Sn 4+ -doped barium hexaferrite according to the stoichiometric formulation BaFe (12−(4/3) x )Sn x O 19 ( x = 0 , 0.6, 0.8 and 1.0) have been studied. The XRD and magnetic analysis, using a rotating sample magnetometer, reveal that a correlation exists between the variation of the host lattice parameters and the decrease in the values of saturation magnetization, remnant magnetization and magnetic anisotropy with Sn 4+ content. This makes it possible to connect the microstructural properties to the magnetic behavior of doped barium hexaferrite at both microscopic and macroscopic levels.

Mechanical damage detection using magnetic flux leakage tools: modeling the effect of dent geometry and stresses

We have used three-dimensional (3D) magnetic finite element analysis (FEA) to simulate the MFL signal from a circular dent geometry with associated residual stresses. Strain distribution information around the dent was obtained from an earlier work using finite element structural modeling. In the magnetic FEA dent model, the localized residual stresses were simulated by assigning appropriate values of magnetic anisotropy to the relevant magnetic regions. The simulated flux leakage patterns were found to be in good agreement with the experimentally observed MFL patterns associated with dent shape as well as with the stress effects from the dent.

High-frequency behavior of amorphous microwires and its applications

A magnetic microwire is a continuous filament of total diameter less than 100 μm consisting of an inner metallic magnetic nuclei covered by a glassy outer shell, usually obtained by Taylor's technique, with interesting magnetic properties connected with its high axial magnetic anisotropy. Magnetic sensors based on microwires used, as operating principle, the strong connection between the composition and the uniaxial anisotropy through a magnetostriction constant such as the large Barkhausen effect, Mateucci effect and giant magneto-impedance effect. The study of the microwave properties is also very promising technologically. In the microwave region (approaching GHz range), the ferromagnetic resonance (FMR) occurs and it is connected with the spin precession of the magnetisation vector due to the effect of the high-frequency electromagnetic field applied such that the magnetic component is perpendicular to the magnetisation vector. The natural ferromagnetic resonance (NFMR) has been also observed. The frequency depends upon the value of magnetic anisotropy and it is characterised by the single well-distinguished line in the 2–10 GHz range. Tags detector based on the microwires FMR and a new kind of electromagnetic radiation absorbers based on the microwires NFMR have been developed.

Dynamic and static magnetic anisotropy in thin-film cobalt zirconium tantalum

The magnetic anisotropy values of thin amorphous cobalt zirconium tantalum (CZT) films were determined from static and dynamic measurements. Dynamic techniques show a rotatable component of anisotropy that decreases with increasing longitudinal bias field from 200 to 0±48A/m (2.5 to 0±0.6Oe). The dynamic value of the anisotropy is important when using CZT in high-frequency magnetic applications. Static values were obtained with an induction-field magnetometer while dynamic values were obtained using a pulsed inductive microwave magnetometer.

Magnetic and electronic properties of a Pt–Co bilayer on Pt(1 1 1)

Atomically thin Co/Pt(1 1 1) interfaces grown at different temperatures are characterized by very different values of perpendicular magnetic anisotropy as a consequence of the local structure and coordination. Here we present a study of the structural, magnetic and electronic properties for interfaces grown in UHV onto clean Pt(1 1 1) in different kinetic conditions. When one monolayer of Co is deposited at 540 K a thermally activated exchange reaction leads to a sharp Pt–Co double interface giving rise to a strong increase of the magneto-optical response with respect to the Co monolayer deposited at room temperature. The results are interpreted in terms of atomic hybridization as detected by valence band photoelectron spectroscopy.

Modification of interface magnetic anisotropy by ion irradiation on epitaxial Cu/Ni/Cu(002)/ Si(100) films

Various x-ray scattering and magnetic measurements were employed to reveal changes in intrinsic structural and magnetic properties on epitaxial Cu/Ni( t)/Cu(002)/Si(100) thin films (t520, 30, 60, and 90 A) before and after 1 MeV C 1 ion irradiation. Torque magnetometer and grazing incidence x-ray diffraction measurements were carried out to understand relation between magnetic and structural properties, respectively. X-ray reflectivity measurements were performed to characterize interface roughness and intermixing. It is observed that effective magnetic anisotropy values of ion-irradiated films are negative over the entire nickel thickness range and the dominant factor of the reorientation of magnetic easy axis from surface normal to surface parallel is reduction of the interface magnetic anisotropy coefficient in spite of decreased interface mixing after ion irradiation.

Magnetic and microstructural properties of the Ti4+-doped Barium hexaferrite

A study of the magnetic and microstructural properties of the M-type Ti4+-doped Barium hexaferrite according to the stoichiometric formulation BaFe(12−(4/3)x)TixO19 with x=0, 0.6, 0.8 and 1.0, has been reported. The XRD and magnetic analysis show a variation of the host lattice parameters and a decrease in the values of remnant magnetization and magnetic anisotropy with Ti4+ content. The behavior of magnetic properties of materials is explained by the combined effect of the coherent rotation of the magnetic domains and the replacements of Fe3+ by Ti4+ ions in the octahedral and tetrahedral sites.

The glass forming abilities and magnetic properties of Fe–Al–Ga–P–B–Si and Fe–Al–Ga–P–B–C alloys

Abstract An investigation of glass forming abilities and thermal properties of Fe 76− x Al 4 P 12 Ga x B 4 Si 4 and Fe 75− x Al 5 P 11 Ga x B 4 C 5 (where x =0, 2, 5) soft magnetic alloys was carried out using melt-spun ribbons of various thicknesses and suction cast rods of various diameters. For the Si-containing alloys, the critical thickness of amorphous ribbon increased from 55 to 110 μm between x =0 and 5. On the other hand, for the carbon containing alloys, increasing x from 0 to 5 resulted in a decrease in critical thickness of amorphous ribbon from 150 to 100 μm. These data allowed the critical diameter of glassy cylindrical samples D c to be estimated for appropriate alloy compositions and these are compared with experimental observations for suction cast rods. The magnetic properties, including the hysteresis loops and coercivity i H c , were determined by dc inductive magnetometry. The results indicate surprisingly low values of i H c , even for partially crystalline samples. On the other hand, the hysteresis loop shapes suggest a relatively large value of magnetic anisotropy. The possible reason for this behaviour is discussed.

Temperature dependence of the magnetic rotation process of kaolinite microcrystals containing paramagnetic impurity ions dispersed in liquid medium

Temperature dependencies of magnetic rotation were measured in micron-sized silicates dispersed in ethanol for two different samples of kaolinite. Magnetic rotation proceeded by balance between thermal agitation energy and magnetic anisotropy energy. Measurements were performed between 195 and 343 K. The field intensity required to achieve magnetic alignment of microcrystals increases with temperature, because of the temperature dependence of paramagnetic anisotropy, and the temperature dependence of thermal agitation energy. The results indicate that the values of magnetic anisotropy of nonmagnetic materials might partially derive from the paramagnetic moments, which derive from paramagnetic impurity ions. The present experiment provides a technical basis for determining the precise values of diamagnetic anisotropy (Δχ)DIA from minerals which have a concentration of paramagnetic ions and do not form a single crystal large enough to allow bulk Δχ measurements. The values of (Δχ)DIA can be obtained by extrapolating the Δχ–T relations, which follow the Curie law, to the temperature limits.