Volume 33, Issue 3, 01 March 1962
Index of content:
- THIN FILMS‐2
33(1962); http://dx.doi.org/10.1063/1.1728637View Description Hide Description
The ferromagnetic resonance spectra of thin films of Permalloy and other materials have been investigated. Frequently more than one maximum in the resonance line is observed. The evidence from various experiments indicates that films with more than one resonance peak are stratified. A simple model in which two layers of film are coupled via the dipole‐dipole interaction is considered.
33(1962); http://dx.doi.org/10.1063/1.1728638View Description Hide Description
Nickel single‐crystal filmsgrown epitaxially on NaCl at elevated temperatures shown anomalously large values for the crystalline anisotropy constant, K 1, as well as for K 1, the perpendicular anisotropy (i.e., the anisotropy resulting from rotation out of the plane of the film). These values decrease to normal bulk values when the films are floated off the rocksalt.
It has been shown by x‐ray diffraction that the as evaporated films exist in a highly strained condition, resulting in a tetragonal distortion of the cubic symmetry. The parameters of the unit cell change from a 0=3.524 A for unstrained nickel to a=b=3.500 A in the plane of the film and c=3.546 A normal to the film. It is also shown that the stress causing this strain is elastic in character and is relieved by floating the film off the rocksalt.
A calculation using bulk elasticity data yields a planar compressive stress σ=−1.2×1010 d/cm2. The magnitude and direction of the stress indicates it results from the difference in thermal expansion between the nickelfilm and the NaCl substrate.
This externally applied stress system influences the magnetic state of the film by contributing to the total energy of the system through a magnetoelastic interaction. Employing the five‐constant magnetostrictive equation, it is shown that a planar compressive stress of this magnitude does result in an anomalously high crystalline anisotropy value, as well as an anomalously high value of the anisotropy perpendicular to the plane of the film.
33(1962); http://dx.doi.org/10.1063/1.1728639View Description Hide Description
Permalloyfilms have been studied to determine composition variations which exist in a direction normal to the substrate surface. These films are formed by a noninterrupted deposition process. They are classified according to the amount of oxygen present on the substrate prior to deposition. If normal care is taken to produce a clean glass substrate, a thin layer of αFe2O3 and NiFe2O4 is produced at the film‐substrate interface. Those films produced on a substrate saturated with oxygen have a thick negative magnetostrictive alloy layer adjacent to the substrate. This nickel‐rich alloy presumably results from the diffusion of oxygen through the depositing films and the formation of iron oxide and nickel ferrite. In addition to the chemical analysis of the films, evidence to support the idea of stratification is found in the etch experiments, resonance data, saturation magnetization measurements, and cross section analysis.
33(1962); http://dx.doi.org/10.1063/1.1728640View Description Hide Description
A discussion of the electrodeposition of alloys of the Ni‐Fe‐Co system is presented. Solutions from which these metals are deposited are described and the role of their constituents discussed. The various applications for these deposited materials is reviewed pointing out their advantages and shortcomings. A detailed description of the electrodepositedthin film is given.
33(1962); http://dx.doi.org/10.1063/1.1728641View Description Hide Description
The anisotropy in the plane of the film of thin films of Ni evaporated on Mo‐covered substrates and of oxidizedNifilms has been measured as a function of field and temperature. At intermediate fields, 200–1200 oe, a large rotatable anisotropy is found, about an order of magnitude larger than the usual magnetic annealinganisotropy. At higher fields the rotatable anisotropy disappears and only the magnetic annealinganisotropy remains. The temperature dependence of the rotatable anisotropy indicates a connection with the antiferromagnetic character of NiO.
33(1962); http://dx.doi.org/10.1063/1.1728642View Description Hide Description
A study of torque curves in thin Permalloy films with hc >0.5, where hc=Hc/H̄k is reported. The behavior of a 1400 A, 77% Ni film with hc =0.9 is discussed as a typical example. For applied fields h>0.5, the torque curves are generally complex and the discrepancies with the Stoner‐Wohlfarth (S‐W) model wide‐spread. For h<0.5, if the film is previously saturated, the torque has a period of 2π in agreement with the S‐W model. However, when 0.3<h<0.5, it is irreversible and the hysteresis is unidirectional, occurring around the easy direction of the bulk of the film. A model is proposed to explain this effect in which it is assumed that the film contains small regions with negative anisotropy −K 2, where K 2 is of the order of K 1, the anisotropy of the bulk of the film. The torque curves calculated for this model are found to agree qualitatively very well with the experimental results.
33(1962); http://dx.doi.org/10.1063/1.1728643View Description Hide Description
Ferromagnetic resonance measurements have been carried out on single‐crystal nickelfilms obtained by epitaxial evaporation on NaCl under various evaporation conditions. Resonance measurements on thin films by previous investigators have yielded anomalous values of 4πM which have tentatively been attributed to stress in the films. In this paper it is shown that there is a second factor which must be taken in consideration to explain the shift in resonance peak.
Films that were grown at high temperatures (400°C) and in good vacuum (10−10 mm Hg) exhibited an apparent saturation magnetization only 60–70% of the bulk value. This is in accord with the results of ferromagnetic resonance experiments of Kuriyama et al., who attempted to explain their results by the presence of large tensile stresses in the films. However, electron microscope studies of filmsgrown under the above conditions indicated that the films formed discrete, well‐separated islands of nickel. The observed particle sizes are such that the demagnetizing factor perpendicular to the film is 60–70% of the value for a continuous planar film. This implies that the shift in the resonance peak was caused not by stresses but by a lowering of the demagnetizing field resulting from the discrete particle growth.
To further substantiate this, continuous filmsgrown at lower temperatures (300°C) and in technical vacuum (10−5 mm Hg) exhibited a magnetization approximately 60% higher than the bulk material values. X‐ray diffraction indicated the presence of large compressive stresses in these films. That the increased magnetization was induced by these compressive stresses was convincingly shown by the decrease of the saturation magnetization to bulk value when the stress was relieved by the introduction of water vapor into the cavity. No such change in the external field at resonance was observed for the discontinuous films under a similar exposure to water vapor.
33(1962); http://dx.doi.org/10.1063/1.1728644View Description Hide Description
Isotropic stress measurements in Permalloyfilms have been carried out as a function of thickness, rate of deposition, and substrate temperature. The measurements were made by clamping one end of a substrate consisting of a thin strip of glass or mica and observing the deflection of the free end during deposition. Results indicate that the stress is independent of thickness in the range 100–2000 A. However, depending upon the values of the other deposition parameters, one may observe either tensile, compressive, or zero stress.
33(1962); http://dx.doi.org/10.1063/1.1728645View Description Hide Description
Hall effectmeasurements on a ferromagneticfilm can be used to examine the normal anisotropy and the distribution of stresses in the plane of the film. The measured Hall voltage exhibits a smooth transition from low to high field regions rather than the sharp crossover, at technical saturation, which is expected of a single domain. Since the ferromagnetic Hall effect depends upon the component of magnetization perpendicular to the plane one can attribute this difference of behavior to a domain structure describable by a distribution of normal anisotropies. The difference between the single and multi‐domain Hall plots depends upon the nature of this distribution and from certain features of the experimentally obtained difference curve one can infer the type and extent of the distribution. If the anisotropy distribution is due to a corresponding range of strains superimposed on the geometric anisotropy of the film one can also estimate the form and extent of the function describing the planar stresses. It is shown that the existence of the anisotropy distribution results in a difference between the field at which the Hall measurements indicate technical saturation and that at which the normal anisotropy distribution is peaked.
33(1962); http://dx.doi.org/10.1063/1.1728646View Description Hide Description
A series of films of composition varying from 72% Ni, 28% Fe to 90% Ni, 10% Fe were evaporated at a pressure of the order of 10−5 mm Hg onto a heated glass substrate (250°C) in the presence of a magnetic orienting field in the plane of the film. The composition was controlled by placing a charge of the selected composition on the filament in an amount just sufficient to make the desired 3000 A film when all of the material was evaporated.
The magnetoelastic behavior of the films was studied by measuring η=ΔHk /(Δl/l), here ΔHk is the change in the anisotropy field upon the application of a stress sufficient to strain the film an amount Δl/l (typically 4×10−5). η was found to decrease linearly with composition to a first approximation with a slope of −26.5×103 oe per percent nickel, with η being zero for a film composed of 81.5% Ni, 18.5% Fe.
The value of η was compared with that of Λ m for bulk material where Λ m is the change in the magnetization divided by the applied stress in the case where the stress approaches zero and where the bulk material is biased by an applied field sufficient to yield the maximum change in Λ. Using bulk data for the saturation magnetization and Youngs modulus the value of η measured here yields a value for Λ m which is too large by an order of magnitude.