Induced in-plane magnetic anisotropy in YIG films

We have studied the symmetry properties of the in-plane induced magnetic anisotropy in {100} and {110} disks of single crystal YIG epitaxially grown on gadolinium gallium garnet (GGG) substrates. The ferromagnetic resonance (FMR) technique was used to determine the values of the cubic and induced magnetic anisotropies. The induced anisotropy is interpreted in terms of a magnetostrictive magnetic potential energy. We find that the effective field induced in the plane of the film is isotropic for {100} disks but for {110} disks the induced anisotropy is uniaxial within the plane.     

Annealing of cylindrical Ni-Fe films

The effect of annealing on the microstructure of cylindrical electrodeposited 81-percent Ni, 19-percent Fe films was studied with the electron microscope. The films were deposited onto 5-mil Be-Cu wires having either Au or Cu intermediate layers. The annealing was performed on both free-standing films and on films still attached to the substrate. The initial change in the free-standing films was a rapid recrystallization. After the whole film had recrystallized, normal grain growth was observed. There is evidence that the driving force for the annealing is provided by stresses present in the films. Films annealed while attached to a Au-Be-Cu substrate did not exhibit recrystallization or grain growth, and the electron microscope studies showed that the Ni-Fe grains were pinned by Be-Au which diffuses into the grain boundaries but does not alloy with the Ni-Fe. The films which were annealed while attached to a Cu-Be-Cu substrate behaved essentially like free-standing films. Electron beam microanalysis and electron diffraction studies revealed that Be-Cu diffuses into the Ni-Fe grain boundaries and then alloys with the Ni-Fe. Recrystallization of the alloy can then take place freely.     

Magnetization in Ni and Ni-Fe thin films

Nickel films have been deposited in conventional high vacuum, ultra-high vacuum, and in controlled contaminant, ultra-high vacuum environments. High field saturation magnetization Msmeasurements on the films made in high vacuum and an oxygen-contaminated ultra-high vacuum system show that they posses low values of Msfor film thicknesses of 1000 Å. The normal moments observed for ultra-high vacuum deposited films lead to the conclusion that the low Msvalues are associated with the oxygen and are caused by a true loss of effective magnetization rather than coupled superparamagnetism or a ripple blocking field. Supplementary torque and ferromagnetic resonance studies on the Ni and two different Ni-Fe compositions also show that the grain boundary perpendicular anisotropy models are not particularly relevant for films made under such nominal technical vacuum conditions.     

Magnetic properties of Ni-Fe films coupled with stripe-domain films

A study was made of the change in anisotropy field, coercivity, angular dispersion, and creep threshold of an ordinary Ni-Fe film when coupled with a stripe-domain film. It was found that the values of these properties all increased as a result of the coupling.     

Induced magnetic anisotropy and strain in permalloy films deposited under magnetic field

Field induced magnetic-anisotropy is a very important but poorly understood property. There have been many hypotheses on the origin of the phenomenon, e.g. strain, atomic pair ordering, etc., but little experimental evidence exist. This study prepares 100 nm thick Permalloy films having the field-induced-magnetic-anisotropy and carefully measure strains, i.e. interplanar distance of crystallographic (111) planes in various directions, using high power synchrotron radiation and precise Grazing Incidence X-Ray Diffraction method. The result delineates that the field-induced-magnetic-anisotropy has a strong correlation with the strain-anisotropy in the film.     

Anisotrophy control of Ni-Fe films through sequenced-field deposition

Anisotropy of nickel-iron films of 82, 74, and 66 per cent nickel compositions was controlled by time-sequenced application of orthogonal fields during deposition. Resulting anisotropy values are in agreement with simpleM-induced anisotropy principles. Coercive forces show small but definite decrease with anisotropy constant. Dispersion angle is proportional to the reciprocal of the anisotropy constant. The technique is suitable for production of low-Hkfilms. It permits nonanomalous inverted films to be produced and allows the study of other anisotropy sources.     

Spin wave measurements of exchange constant in Ni-Fe alloy films

The ferromagnetic exchange constant has been measured using spin wave resonance in a number of iron-nickel alloys covering the composition range 60% to 90% nickel. The exchange constant varies smoothly from a value of 1.3 (10^-6) erg . cm^-1at 60% Ni to an extrapolated value of 0.77 (10^-6) at 100% Ni. The data are in significant disagreement with the values published by Rusov.     

The influence of sample geometry on the magnetoresistance of Ni-Fe films

The magnetoresistance of Ni-Fe (81–91) films has been measured as a function of film geometry (thickness to width ratio N). It has been found that under the condition of large magnetization dispersion the behaviour of films with a high value of N differs distinctly from that of films with N ≈ 0. Moreover, the easy axis coercive force H_c increases markedly when the width of the film is of the order of 20 μm and less.     

A model of magnetostriction interaction in thin double-layer magnetic films of Ni-Fe alloy

Under the assumption that in a double-layer film both layers are equally deformed, the following formula for the magnetostriction energyE = K_{c} sin^{2} alphahas been derived whereK_{c} = (9/40)(2U'U"/U'_{0} + U_{0}")is the coupling constant and α is the angle between the magnetization vectors. This formula is valid if we can neglect interaction with the substrate. The sign of the coupling constant is discussed. It turns out that where the composition of the two layers are different, the value of Kccan be, in some special cases, negative.     

Perpendicular anisotropy of evaporated magnetic films

Evidence of the existence of origins of perpendicular anisotropy other than the ordinary magnetostrictive effect is presented with a brief review of other studies. As one of these origins, the effect of the grain boundaries or the microscopic shape effect is discussed. The amount of perpendicular anisotropy observed in the stripped films does not seem capable of explanation by this effect only.     

Annealing behavior of magnetic anisotropy in CoNbZr films

The effect of magnetic and nonmagnetic annealing on the magnetic anisotropy in CoNbZr films, formed by a DC opposing-targets sputtering method, was investigated. It was revealed that the origin of the magnetic anisotropy is the directional ordering of the magnetic atoms. The anisotropy fields and the direction of the easy axis obtained when the films are annealed in zero magnetic field are almost the same as those for the magnetic field parallel to the easy axis of the as-deposited films. When the films are annealed in a magnetic field perpendicular to the easy axis, the anisotropy field induced in parallel with the magnetic field, H_k(t), is well represented by the following formula: ln {1-H_k(t )/H_k(∞)∝-√Tt, where H_k(∞) is the thermal equilibrium value of the anisotropy field and D is the diffusion constant. The activation energy of the as-deposited film is 0.86 eV. Annealing the film increases the activation energy which is 2.1 eV when the film is annealed at a temperature of 450°C for 2 h     

Domain splitting in thin films with in-plane anisotropy

Splitting of magnetic ripple into domains due to an external magnetic field was observed using the defocused electron microscopy method. The tested film was magnetized perpendicularly or parallel to the easy axis of the uniaxial anisotropy, and both the magnetic field direction and the anisotropy axis lay in the film plane. Splitting of the ripple into 1 μm domains was mainly reversible until the value of ripple amplitude reached 0.5 rad. Movements of the Néel walls and Néel-Bloch-Néel transformation of the domain walls were the main irreversible phenomena which led to hysteresis. Domain splitting of the ripple is properly described only by a Riedel model which includes the interactions between cores and tails of the periodically arranged Néel walls.     

Magnetic properties of Ni-Fe films prepared by a DC triode sputtering method

The magnetic properties of Ni-Fe films with 81-wt.% Ni prepared by a DC triode sputtering method are studied as functions of sputtering parameters. Two kinds of substrates are used: one is flat and the other is patterned. In the former case sufficiently low coercive forces are obtained when both the target voltage and the Ar pressure are kept below the critical values. In the latter case, a negative substrate bias voltage is necessary to improve the magnetic properties in addition to the previous conditions.<>     

Effect of a composition gradient on the magnetoelastic sensitivity of Ni-Fe films

Measurements of the magnetoelastic sensitivity of electrodeposited 1 μ cylindrical Ni-Fe films indicate that the magnetostriction of these films becomes more positive upon annealing. A composition gradient has been observed through the thickness of these films. In addition, electron diffraction results indicate that the composition gradient is substantially reduced during an anneal at 250 °C. To understand the change in magnetoelastic sensitivity the effect of the composition gradient has been considered. The change in the magnetoelastic sensitivity due to the elimination of the composition gradient is shown to be in agreement with observed changes.