Reorientation Of Easy Axis Research Articles

Shape effect on the magnetic anisotropy of an array of epitaxial (10·0) Co dots

The competition between the magnetocrystalline and shape anisotropies was studied by using a submicron-size epitaxial (10/spl middot/0) Co rectangular dots array. The measured torque curves exhibit the magnetic anisotropy with a four-fold symmetry, indicating a clear magnetic easy-axis reorientation. The results were successfully interpreted by taking into account the first order magnetocrystalline, shape and non-negligible second order magnetocrystalline anisotropies.

Magnetic properties of RZn with R=Tb/sub 1-x/Dy/sub x/ (0≤x≤0.6) and R=Tb/sub 1-y/Gd/sub y/ (0≤y≤0.4)

Magnetization, Young's moduli, and magnetostriction were measured on polycrystalline samples of Tb/sub 1-x/Dy/sub x/Zn and Tb/sub 1-y/Gd/sub y/Zn. The easy axis phase boundary was determined for 0/spl les/x/spl les/0.6 and 0/spl les/y/spl les/0.4. To derive temperature dependencies of Young's moduli, small transducer rings were excited into resonance at frequencies /spl sim/100 kHz. Estimated magnetomechanical coupling factors of polycrystalline Tb/sub 0.8/Gd/sub 0.2/Zn in the region of easy axis reorientation are /spl sim/0.6. Magnetostrictions of polycrystalline TbZn at 77 K saturated at /spl sim/0.2% with relatively low fields (/spl sim/1000 Oe), even for compressive stresses >40 MPa.

Induced transverse magnetic anisotropy and domain structure in Co-based amorphous ribbons

The influence of transverse magnetic field annealing on a domain structure, the value of the induced transverse magnetic anisotropy K u, coercivity and magnetic remanence of Co 71.5Fe 2.5Mn 2Mo 1Si 9B 14 amorphous ribbons of different widths (6, 11, 15 mm) has been investigated. Near-full reorientation of the ribbon easy axis from the longitudinal to the transverse direction and the highest value of K u = 110 J/m 3 were obtained for the transverse magnetic field H T = 160 kA/m. On the other hand, only partial reorientation of the easy axis was developed for smaller values of H T. In the initial magnetizing field range, the magnetization process proceeds by reversible rotation of the magnetization vector for H T = 160 kA/m. Domain wall movements are predominant for H T = 8 and 40 kA/m.

Effect of magnetic domain configuration on read-back amplitude variations in inductive film heads (abstract)

Narrow track width, high-performance inductive film heads exhibit a noise phenomenon in which the read-back peak amplitude varies after writing with the head. This noise phenomenon was studied in 6- to 8-μm track width, 31-turn double layered coil, film heads using a scanning Kerr effect microscope. These heads, made from electroplated permalloy films with a magnetostrictive coefficient of − 1.6 × 10−6, were specially selected for the study to have varying levels of read-back amplitude variation by using the percent variation in the peak amplitude after repeated writes as a quantitative noise figure. A statistical sampling method was used to quantitatively measure the magnetic domain patterns in the top NiFe layer of the heads under simulated operating conditions. Quantitative correlation was found between the read-back variation and the magnetization orientation in the narrow-sloped pole region. The images show that a single 180° domain wall orientated longitudinally to the flux conduction direction in the narrow pole piece is the major source of read-back variation in these types of heads. The statistical sampling method shows that the pole domain configurations are reproducible in both the low-noise and high-noise heads. Patterned NiFe films on planar alumina substrates have the desired transverse oriented 180° domain wall configuration in the pole-shaped region, as found in the low-noise heads. These results imply that the variation of the domain configuration in the pole region is caused by easy axis reorientation due to variation in the stress-induced magnetic anisotropy in that region. We also find that the read-back noise is not sensitive to the longitudinal 180° walls found near the back closure region of the heads. This is probably due to the lower flux densities found in the back closure as compared to the pole region and the existence of other flux paths that circumvent the domain walls in the back closure region. We conclude that read-back distortion noise in 6-μm track width heads can be drastically reduced by maintaining a transverse magnetic easy axis in the sloped pole piece by either employing fabrication methods that control the stress state of the pole region or by using very small magnetostriction values in the NiFe films.1

Low temperature crystal and magnetic structures of Ho 2Fe 14B

Ho 2Fe 14B belongs to the hard magnetic material series and, like the prototype neodymium compound, exhibits a spin reorientation transition phenomenon. An accurate neutron diffraction experiment performed on a single crystal allows us to establish the exact low temperature non-collinear magnetic structure. Moreover, a lower crystal symmetry (space group Cm) is shown to occur far above T = 58 K, the spin reorientation transition. The previously reported tetragonal symmetry (space group P4 2/ mnm) can be regarded as a reasonable approximation at room temperature. High magnetostrictive forces and negative Ho-Ho interactions make possible such a crystal and magnetic symmetry lowering that is complicated by the low temperature easy axis reorientation induced by high order CEF terms.

Easy-axis reorientation in the BaCo2-W hexagonal ferrite

The rotation of the magnetization in the BaCo2Fe16O27-W–type hexagonal ferrite has been studied by neutron powder diffraction and single-crystal magnetic measurements in the 2–833 K temperature range. From neutron powder diffraction data the magnetic structures were determined. Up to 453 K, the magnetic arrangement is constant: it is collinear, making an angle (θ=70.0±1.5°) with the hexagonal c axis. Then a continuous rotation of the magnetization towards this axis occurs, ending at T=553 K. From magnetic measurements, the magnetocrystalline anisotropy constants are determined between room temperature and 623 K and the angles between the easy magnetization axis and c axis are deduced. They confirm the rotation of the magnetization.

The influence of easy direction of magnetisation on 59Co NMR spectrum in R2( Co1− xMnx) 17 compounds

The spin echo NMR spectra of 59Co in R 2(Co 1- x Mn x ) 17, (R = Y, Gd) measured at 4.2 K are reported. The large shift of resonance lines is observed, that is explained as caused by reorientation of easy axis of magnetisation from easy plane to easy direction ( c axis). It is suggested to explain quantitatively the spectra, that only two of four Co sites (9d and 18f) in R 2Co 17 structure play a dominant role in determining of anisotropy energy and the Co atoms at the 6c sites (“dumb-bell” atoms) give no direct contribution to the anisotropy energy of the compound. The corresponding changes of local anisotropy energy and the orbital part of cobalt magnetic moment characteristic for each of cobalt structural sites are calculated and discussed.