Magnetic Anisotropy Factors Research Articles

Influence of composition on the structural, magnetic and magnetotransport properties of nanostructured Co-Ag films fabricated by electrodeposition technique

Evolution of structure, granular size, magnetoresistance and magnetization behavior of electrodeposited Co-Ag coatings with changing cobalt concentration from 19.07 to 47.02 at.% is offered. The heterogeneity of the deposits was verified through the utilization of structural techniques, including X-ray diffraction and transmission electron microscopy, revealing a size distribution ranging from superparamagnetic to ferromagnetic particles. The coatings were found to contain both fcc-Ag and fcc-Co. As the concentration of Co in the films increases, the size of the magnetic granules also increases while the distance among them simultaneously is reduced. The magnetic force microscopy indicates that magnetic domains exist which are significantly larger than actual particles. The highest giant magnetoresistance (GMR) amplitude was observed in coatings with a cobalt concentration of 33. 12 at. %. The studies on dc-magnetization obviously recognized the existence of perpendicular magnetic anisotropy. With increasing cobalt concentration beyond 33.12 at. %, the strength of perpendicular magnetic anisotropy decreases, while the anisotropic magnetoresistance (AMR) increases. The observed perpendicular magnetic anisotropy and complex magnetoresistance behavior in the Co-Ag films can be explained by the transition in the nature of magnetic interaction from dipolar to ferromagnetic interactions. Moreover, results indicate that the coercivity of Co-Ag films decreases with increasing the Co concentration up to 33.12 at. %, but begins to increase with further increasing Co concentration in the Co-Ag coatings. we calculated the first and second magnetic anisotropy factors based on the magnetization curves.

Structure and size effects in the magnetic anisotropy factors of Co-Ag nano granular films

Structure and size effects in the magnetic anisotropy factors of Co-Ag nano granular films

Fabrication and magnetic properties of Co based thin films synthesized by physical vapor deposition under vacuum

We used thermal heating process, under a pressure of 10−7 mbar, to fabricate thin films of cobalt on monocrystalline silicon Si (100) substrates. The incident beam strikes the substrates under normal and oblique incidences within a home-made evaporation chamber. The thickness of the deposited films ranges from 18 to 400 nm. Microscopic characterizations of the films are performed with X-ray diffraction (XRD) measurements and infer that all the samples are polycrystalline, with an hexagonal close packed (h.c.p.) structure and exhibit a <0001> preferred orientation, for the perpendicularly evaporated films. The grain size is found to increase with the thickness of the magnetic layer. The values of the computed parameters allow concluding to a compressive stress for the thinnest films. 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.) tools. The dynamic magnetic properties have been investigated using Brillouin Light Scattering (B.L.S.) measurements. The M.F.M. observations were performed after in-plane ac demagnetization, and stripe patterns are only observed for the thickest films, showing the weaker perpendicular anisotropies. We used the experimental results provided by these tools to compute the effective magnetic anisotropy factors Ku . Values of Ku anisotropy constants, higher than 13 × 106 erg.cm−3, have been found.

Magnetic anisotropy factors of vapor deposited CoCr thin films on Si and glass substrates

Series of CoxCr1−x thin films have been evaporated under vacuum onto Si (100) and glass substrates. An alternating gradient field magnetometer is used to characterize the static magnetic properties of the samples and Brillouin light scattering is used to study their dynamic magnetic properties. The in-plane easy magnetization axis is found for all samples. Using these results, we computed the first, second and uniaxial magnetic anisotropy factors by several methods. Values of the computed effective magnetic anisotropy factors higher than 106ergcm−3 have been found. The results are discussed and correlated.

Thickness Dependent Magnetic and Structural Properties of CoxCr1–x Thin Films Evaporated on Si(100) and Glass Substrates

Series of Co(x)Cr(1-x) thin films have been prepared by thermal evaporation onto Si(100) and Corning glass substrates, x ranging from 1 to 0.60, and the magnetic layer thickness from 17 to 220 nm. The dependence of the magnetic and crystallographic properties on the thickness of CoCr layers have been investigated. The chromium content effect on the saturation magnetization of the films has also been examined. Microscopic characterizations of the films, performed with X-ray diffraction (XRD) measurements, infer that all the samples are composed of hcp phase crystallites with good orientation of the c axis showing a (0001) preferred orientation. The grain size increases with thickness. Atomic force microscopy (AFM) observations show very smooth film surfaces, the highest rms value being 18 amgstroms. The saturation magnetization M(s) was found to decrease from 1400 emu/cm3 to a few emu/cm3 as x decreases from 1 to 0.60, for all values of the thickness. In-plane squareness up to S = 0.83 has been observed for the CoCr/Si thinnest film, and S = 0.90 for the Co/Si thinnest film, too. Magnetic Force Microscopy (MFM) study points out the absence of stripe domains equilibrium magnetization structure for the CoCr thin films whereas the thick Co films present a well defined stripe pattern. From the magnetocrystalline anisotropy field H(a) values extracted from the fit of the BLS spectra, we have computed effective magnetic anisotropy factors K(u), as well. Their negative values for the CoCr samples confirm an in-plane magnetic anisotropy for the thin film magnetization.

Structural, static and dynamic magnetic studies of evaporated CoxCr1x/Si (100) and CoxCr1x/glass thin films

We have evaporated a series of CoxCr1-x thin films under vacuum onto Si (100) and glass substrates, with a perpendicular incidence. The thickness of the magnetic layer ranged from 17 to 220 nm, and the content chromium, from 0.12 to 0.20, values determined by means of Rutherford Backscattering Spectrometry (R.B.S.) spectra using SIMNRA programme. Microscopic characterizations of the films were done with X-ray diffraction (XRD) measurements and infer that all the samples were polycrystalline, with an hcp structure and show a <0001> preferred orientation, and with the grain size increasing with the chromium content decrease. Atomic force microscopy (A.F.M.) observations reveal very smooth film surfaces. The static and dynamic magnetic properties have been investigated by means of Alternating Gradient Field Magnetometer (A.G.F.M.), and Brillouin Light Scattering (B.L.S.) measurements. The saturation magnetization MB was found to decrease from 1200 emu/cm3 to 220 emu/cm3 as the chromium content increases from 12%at. to 20%at, whatever the thickness is.From the fit of the B.L.S. spectra, we have computed effective magnetic anisotropy factors, as well. All the results are discussed and correlated.

Magnetic characterization of cold rolled and aged AISI 304 stainless steel

Magnetic easy axis predicted by the orientation distribution of the maximum amplitude of magnetic Barkhausen emission (MBE), which is obtained by magnetization in radial directions from the center of the specimens has been applied to determine the magnetic anisotropy on cold rolled and aged 304 SS in two sets of specimen. The maximum of the MBE has been found to orient along the rolling direction (RD) compared to the transverse direction (TD), indicating the presence of magnetic easy axis along the rolling direction for both sets. The strain induced martensite phase transformation has been determined using X-ray diffraction technique. The orientation distribution function (ODF) analysis has been carried out to obtain the crystallographic texture with cold rolling. ODF analysis revealed the 〈110〉 texture as the major. The magnetic anisotropy factor has also been determined with cold deformation and noticed that the strength of magnetic anisotropy decreases above 50% deformation for both the sets. Results have been explained considering two competitive effects, formation of crystallographic texture in the martensite phase and presence of compressive residual stresses along RD during cold rolling.

Ｆｅ‐ｐｏｏｒ組成Ｍｎ‐Ｚｎ‐Ｔｉフェライトの初透磁率の周波数依存性

Initial permeability, permittivity and resistivity spectra of Mn-Zn-Ti ferrite with Fe-poor composition (less than 50 mol% of Fe2O3) (FPF) are compared with Fe-rich Mn-Zn ferrite and Ni-Zn ferrite.Analysis of the electromagnetic characteristics shows that the skin effect and dimensional resonance can be disregarded for FPF of the measured sample size below 1 MHz.The contribution of the domain wall and spin rotation resonance to the permeability spectra was estimated by numerical fitting of the permeability data. It was found that natural resonance occurred in FPF, as in Ni-Zn ferrite. In addition, FPF has a damping factor β smaller than the conventional Fe-rich Mn-Zn ferrite, because it does not contain Fe2+ ions that have non- zero orbital moment, and large magnetic anisotropy factor.

Depth-dependent lattice parameter variation and stress-induced magnetic anisotropy of ultrathin Dy2BiFe4GaO12 garnet films deposited on the glass substrate by pyrolysis

Lattice parameter variation as a function of depth from the free surface of ultrathin Dy2BiFe4GaO12 garnet films for magneto-optic application has been investigated. These thin films were synthesized by pyrolysis on the glass substrate and annealed at 660 °C in the glass transition range. The lattice parameters were determined by grazing incidence x-ray in asymmetric Bragg diffraction. X-ray diffraction results show that film stress is compressively greater near the glass/film interface and becomes smaller in magnitude toward the free-film surface. This observation has been interpreted as a result of softening of the glass substrate during annealing in the glass transition range and the subsequent larger shrinkage of the glass substrate with respect to the deposited crystalline film upon cooling. The thermal expansion difference between the substrate and the deposited film can in turn cause the stress-induced magnetic anisotropy. The induced magnetic anisotropy factor Ku has the maximum value above a threshold film thickness, about 600 Å. Down to this limit, Ku increases with the decreasing film thickness.

Crystallisation of BaFe 12O 19 hexagonal ferrite with an aid of B 2O 3 and the effects on microstructure and magnetic properties useful for permanent magnets and magnetic recording devices

Polycrystalline Ba-ferrite (BaFe 12O 19) using B 2O 3 (up to 1 mol) as a sintering aid has been prepared by the usual solid state reaction of BaCO 3 and Fe 2O 3. The B 2O 3, which exists in molten form during the reaction (operated at 1000–1400°C), dissolves the reactants in intimate contact. The dissolved solid and molten B 2O 3 both diffuse into the system to facilitate the reaction, BaCO 3+6 Fe 2 O 3 ⇋ BaFe 12 O 19+ CO 2, of ferrite formation. The reaction is very sensitive to B 2O 3 addition and temperature ( T s) employed for the sintering. The distortion of Ba-ferrite lattice, that usually appeared due to sintering at higher temperature, T s ⩾1300° C, is considerably reduced by the use of B 2 O 3( x) ⩽0.3 mol addition. The distortion however appears for the intermediate B 2O 3 content of 0.3 mol ⩽ x<0.7 mol. A model for the reaction based on the experimental results of X-ray diffractometry and microstructure of the samples is proposed. It accounts successfully for the crystallisation of magnetic particles and variation in the magnetic anisotropies. The effect of B 2O 3 additions to Ba-ferrite is reflected by the increase of magnetisation M s (by ≈13%) and the decrease of coercivity H c (to as small as 5 Oe), subjected to the sintering especially at higher T s. The materials obtained with M s as large as 79 emu/ g and H c =4−3 kOe ( at 25° C) are suitable for the use as permanent magnets, whereas those comprising small H c of ≈1 kOe can be useful for magnetic recording applications. The increase of M s is explained by invoking the fact that B 2O 3(B 3+) substitutes on Fe 3+ (tetrahedral) sites according to BaFe 12−yB yO 19, with y up to 0.4 (equivalent to x ≈ 0.2 mol). The substitution (B 3+→Fe 3+) causes distortion in the tetrahedral sites within the crystal unit cell as evidenced by the EPR spectroscopy. We also developed an empirical relation describing the EPR linewidth (Δ H) in Fe 3+ ferrimagnetic resonance at g ≈ 2.5 and the various magnetic anisotropy factors. This enables us to analyse for the anisotropy factors by using the observed values for Δ H, H c and M s.

Magnetic anisotropy measurement with an oscillation magnetometer

A method of using an oscillation magnetometer to determine magnetic anisotropy factors in the plane of a thin disk-shaped sample lying in the X - Z-plane is described. Both the saturation magnetization, M0, and the factor (Nx - Nz)M0 may be obtained independently; Nx, Ny and Nz are demagnetization factors which include all contributions to magnetic anisotropy such as those arising from stress, magnetocrystalline anisotropy and shape. These results are correlated with previous work on a somewhat different type of oscillation magnetometer used to determine (Ny - Nz)M0, and it is shown that a correction must be applied for both types of magnetometer when the oscillation amplitude exceeds a degree or two. Finally, it is shown that the oscillation magnetometer can be employed to determine the details of any angular dependence of magnetic anisotropy in the plane of the sample if such anisotropy is sufficiently large. These measurement techniques are particularly applicable to the determination of any dependence of M0 on film thickness in thin ferromagnetic evaporated films, and to the determination of magnetic anisotropy in thin films evaporated and/or annealed in a magnetic field.