Anisotropy In Nickel Research Articles

Magnetomechanical effects under torsional strain in iron, cobalt and nickel

The change of magnetization as a function of applied torque has been investigated for cylindrical rods of 99.9% pure iron, cobalt and nickel. The relationship between the magnetomechanical effect and magnetostriction in these materials has also been investigated. Torque was applied with amplitude up to ±5 N m with no associated bending moment. The magnetic field near the sample surface was measured using a Hall effect sensor at the center of the sample. The results showed a linear dependence of this field on torque once the transient effects of the first few stress cycles had been overcome. The derivative of the surface circumferential magnetic field with respect to torque for a nickel rod was 19 A N −1 m −2. Cobalt and iron, on the other hand, showed smaller sensitivity to torsional stress, with changes less than 1 A N −1 m −2. The difference in behavior is due to the higher ratio of magnetostriction to anisotropy in nickel. Magnetostriction measurements were made and it was found that the piezomagnetic coefficient d, that is the slope of the magnetostriction curve d λ/d H, at low magnetic field is an important figure of merit in determining sensitivity of magnetization to torque. It is shown that the sensitivity of magnetic induction to stress d B/d σ is dependent on the ratio of magnetostriction to anisotropy.

Magnetic anisotropy in nickel and cobalt films obliquely deposited by sputtering

The in-plane magnetic anisotropy was investigated in nickel and cobalt films obliquely deposited by rf diode sputtering. The incidence angle was 45° and the substrate temperature Ts ranged from 305 to 623 K. At a pressure of 10 Pa, a uniaxial anisotropy with the easy axis parallel to the incidence plane is induced in nickel films. The magnitude of the anisotropy decreases with increasing Ts. Its origin is the anisotropic stress, since optical and electrical measurements and the X-ray analysis showed negligible contributions of the shape anisotropy of crystallites and the preferred orientation. In cobalt films, on the contrary, the magnetic anisotropy is extremely small irrespective of Ts. However, by increasing the pressure (20–26 Pa) we could obtain a large anisotropy with the easy axis perpendicular to the incidence plane at the low Ts range (Ts≤ 360 K). The {0002} pole figure revealed that this anisotropy originates from the c-axis alignment.

Formation of biaxial anisotropy in nickel by plastic deformation

An explanation is given of the behavior with applied magnetic field of the weak biaxial magnetic anisotropy observed in pure polycrystalline nickel after plastic deformation. This explanation is based on the analysis of the superposition of torque curves corresponding to regions of orthogonal uniaxial magnetic anisotropies of magnetoelastic origin, produced by residual microstresses in tensile and compressive regions. These generate a biaxial torque curve in unsaturated specimens. This analysis explains some features of the observed biaxial anisotropy that cannot be understood by supposing that its origin is due only to a preferred orientation (texture) of the subgrain structure.

A measurement of the surface energy anisotropy of nickel by transmission electron microscopy of field emitter crystals

A measurement of the surface energy anisotropy of nickel by transmission electron microscopy of field emitter crystals

Torque terms and grain-boundary energy measurement

The surface-energy anisotropy of nickel at 1000°C has been re-determined from measurements of the shape of twin boundary-surface intersections. The measurements were used to correct measurements of the energy of seventy-one individual grain boundaries made on the same specimen, for torque-term effects. The average correction to individual grain boundaries was 20%, but the effect of the torque-term corrections on the average value of the grain boundary/surface-energy ratio was less than the experimental error in the ratio.

Formation of Uniaxial Magnetic Anisotropy in Nickel by Plastic Deformation

Previous plastic elongation, or compression, of polycrystalline nickel was found to produce a uniaxial anisotropy. The easy axis of magnetization was parallel to the axis of previous elongation and at right angles to the axis of previous compression. The maximum value of the uniaxial anisotropy energy constant Ku was about 2700 erg/cm3 after 2.5% elongation. The observed anisotropy is shown to be due to a particular distribution of residual microstress, in which most of the volume of the specimen is in residual compression, balanced by a small volume in tension, after plastic elongation. These stresses, although balanced, introduce magnetoelastic effects which do not cancel in a nonsaturated specimen, and which thereby cause the observed anisotropy. Evidence for the assumed stress distribution was obtained by x-ray diffraction.

The Formation of Uniaxial Anisotropy in Nickel by Plastic Deformation

Previous plastic elongation, or compression, of polycrystalline nickel was found to produce a uniaxial anisotropy. The easy axis of magnetization was parallel to the direction of previous elongation and at right angles to the direction of previous compression. The maximum value of the uniaxial anisotropy energy constant Ku was about −2 700 erg/cm3 after 2.5% elongation. The observed anisotropy is shown to be due to a particular distribution of residual microstress, in which most of the volume of the specimen is in residual compression, balanced by a small volume in tension, after plastic elongation. These stresses, although balanced, introduce magnetoelastic effects which do not cancel in a nonsaturated specimen and which thereby cause the observed anisotropy. Evidence for the assumed stress distribution was obtained by x-ray diffraction.

On the Origin of M‐Induced Anisotropy in Nickel and Permalloy Films

AbstractThe anisotropy field strength HK is measured in thin nickel and 81/19 nickel‐iron films immediately after deposition and during subsequent systematic annealing in external magnetic fields. These measurements are performed with the films kept in ultra high vacuum using a planar Hall effect method. An analysis of the HK‐isotherms and of the temperature dependence of HK gives the spectrum of HK‐contributions of a given film with their relaxation times and activation energies. In non‐magnetostrictive permalloy the main contribution to the anisotropy (of 60 to 85%) is attributed to directional ordering of the iron pairs. In nickel a complicated concurrence of several anisotropy contributions is found. The contribution of the magnetoelastic energy dominates; it can be understood in terms of the constraint model.