Index of content:
Volume 34, Issue 4, 01 April 1963
- THIN FILMS‐1
34(1963); http://dx.doi.org/10.1063/1.1729367View Description Hide Description
The energies of Bloch and Néel walls are calculated as functions of the film thickness and the angle through which the magnetization turns in the wall. It appears that in addition to the well‐known Bloch—Néel wall transition as a function of the film thickness, Bloch—Néel wall and cross tie—Néel wall transitions occur when the angle through which the magnetization rotates is changed by an external field. The new calculations together with a review of previous work give a comprehensive picture of the domain walls in thin Ni—Fe films.
34(1963); http://dx.doi.org/10.1063/1.1729368View Description Hide Description
The magneto‐optic rotation of light reflected from thin ferromagnetic films has been found to depend on the optical properties of the substrate as well as the optical properties of the ferromagnetic material. Rotations greater than the thick film longitudinal Kerr rotation were observed at certain thicknesses of ferromagnetic films deposited on silver surfaces.
Checkerboard Domain Patterns on Epitaxially Grown Single‐Crystal Thin Films of Iron, Nickel, and Cobalt34(1963); http://dx.doi.org/10.1063/1.1729369View Description Hide Description
Domain structures of epitaxially grown single‐crystal thin films of iron,nickel, and cobalt are investigated by the Bitter pattern technique. In the case of iron and cobaltfilms of (001) orientation, checkerboard patterns are observed, from which the sign of the anisotropy constant can be determined. In the case of nickel, however, no such regular patterns were observed. On Nifilms with (110) orientation, however, one can observe an elongated domain in the  direction. This seems to indicate that a  wall has a higher energy than a  wall. The 180° walls in thin films are unstable and tend to have fine structures.
34(1963); http://dx.doi.org/10.1063/1.1729370View Description Hide Description
Longitudinal permeability is defined as , where BL is the component of applied field parallel to the easy axis, and HT is a bias field applied perpendicular to the easy axis of a magnetic film with uniaxial anisotropy. The longitudinal permeability is also the hard axis resonance amplitude in the low frequency limit.
The longitudinal permeability is calculated using three different models. The first, that of an ideal single domain film, yields an infinite value when the bias equals HK . Considering the effect of inhomogeneity in easy axes, resulting in many noninteracting domains, gives a maximum , where and α90 is so defined that 90% of the film has a local easy axis within α90 degrees of the average easy axis. Including variation of HK within a film lowers μ L /μ T at , where Δ90 is defined so that 90% of the film has an HK within Δ90 HK of the average HK of the film.
Comparison with experimental curves for films with measured values of α90 and Δ90 shows that the last model yields good qualitative agreement and correctly predicts the behavior of μ L /μ T with finite drive fields, but quantitatively the experimental maxima are 20% to 60% lower than the theoretical curves. This difference is attributed to wall energy terms which are not included as part of the regular calculation.
34(1963); http://dx.doi.org/10.1063/1.1729371View Description Hide Description
The quasistatic magnetic characteristics of thin Permalloyfilms have been investigated using a sensitive automatic magnetic torque balance. The most striking feature of the many films investigated in the thickness range below 250 Å is their similarity to thicker films. The data for K are essentially constant until about 80 Å where it drops quickly and smoothly to zero at about 30 Å. The value of the magnetization as a function of thickness supports that of Seavey and Tannenwald, obtained from microwaveresonance absorption. The value of the longitudinal coercive force as a function of thickness exhibited a spread of values typical of thicker films of this particular fabrication procedure. Slight dependence on thickness could be observed in general agreement with the data of Behrndt.
34(1963); http://dx.doi.org/10.1063/1.1729372View Description Hide Description
Interactions between parallel Néel walls in sandwich‐type films were measured by transmission electron microscopy. A lower limit for the true interaction field was measured to be 3 Oe for two 100‐Å films of 80–17–3 Ni–Fe–Co separated by a 100‐Å layer of carbon. This experiment was limited by the coercive force of the two films. A locked‐in wall and domain configuration is described which prevented destruction of interacting walls. Escape fields in excess of 33 Oe (upper limit of the experimental apparatus) were measured for this type of structure. Based on the pair of linear dipoles model, the calculated escape field is 425 Oe. Other models, based on the interaction between linear dipoles and a uniformly distributed sheet‐of‐charge dipole, give similarly high escape fields. It is shown that the maximum interaction energy approaches the wall energy in magnitude, so that the effect on individual wall energies and widths resulting from the interaction of two walls should be included, although the effect of the interaction on the walls is shown to have a minor effect on calculated escape fields.
34(1963); http://dx.doi.org/10.1063/1.1729373View Description Hide Description
A 90° curling of the magnetization is found in magnetic films of 550 Å and less. This rotation takes place in a distance of the order of tens of microns. It provides a basis for the explanation of at least three distinct phenomena, the absence of closure domains at the film edge, the ending of domain walls before the film edge is reached, and the structure of 360° walls. Other experiments dealing with the motion of domain walls can also be explained on the basis of magnetization curling. Experimental curling distances at film edges are compared with those found from a theoretical model. The qualitative and quantitative experimental evidence is in reasonable agreement with theoretical predictions.
34(1963); http://dx.doi.org/10.1063/1.1729374View Description Hide Description
Films of Co–Ni–P with thicknesses from 0.020 to 3 μ and showing unusual magnetic properties have been prepared by electrodeposition onto polished brass substrates. The crystallite size was very small (∼100 Å); no crystallographic orientation could be detected. The coercivity, in the range 375–600 Oe, increased steeply with thickness from 0.020 to 0.1 μ, then decreased logarithmically with increasing thickness. The remanencecoercivity behaved similarly. The ratio of remanent intensity to saturation intensity was high (∼0.70–0.80), the sides of the loop were almost vertical, and yet the films were completely isotropic in the film plane. This combination of properties in films of high coercivity is difficult to explain in terms of existing theories of magnetization reversal.Torque curves were measured and showed a weak sinθ dependence at fields less than the coercivity and a weak sin2θ dependence at higher fields. Graphs of rotational hysteresisW as a function of applied field had a shape which was, in general, independent of film thickness. The peak occurred at about 600 Oe and the maximum anisotropy field was ∼6500 Oe. Calculation of the rotational hysteresis integralgave values which ranged from 1.9 for the thin films to 4.8 for the thicker ones. Models for magnetization‐reversal processes in these films are discussed.
34(1963); http://dx.doi.org/10.1063/1.1729375View Description Hide Description
A set of experiments have been performed to examine the relationship between various types of Permalloyfilms which are usually regarded as being quite separate. The three types are (i) uniaxial films, (ii) inverted films, and (iii) rotatable initial susceptibility (RIS) films. It is postulated from the results of these experiments that the three films differ by the KV fraction of randomly oriented material present. At one extreme, the uniaxial films have a very low random KV fraction, while at the other extreme, RIS films are completely random arrays. The inverted films can be regarded as being intermediate between these two types. The origin of the high remanence observed in the inverted and RIS films is theoretically attributed to the effects of magnetostatic interactions between adjacent regions with different easy directions.
34(1963); http://dx.doi.org/10.1063/1.1729376View Description Hide Description
The unidirectional rotational hysteresis in a uniaxial Permalloy film has been studied as a function of a rotating steady field and a steady field in the bulk easy direction. Observations were made of both the angular bounds and the magnitude of the unidirectional rotational hysteresis. The results are consistent with a model in which the film is considered as being a uniaxial matrix containing a small volume fraction of regions with randomly oriented anisotropies. The effect of the matrix on the regions is taken as being a field parallel to the magnetization of the matrix.
34(1963); http://dx.doi.org/10.1063/1.1729377View Description Hide Description
Ferromagnetic resonance absorption in thin Permalloyfilms has been studied at frequencies from 1 to 50 Mc with the steady magnetic field applied perpendicular to the plane of the film. This technique provides a direct means of measuring the saturation magnetization since the rf resonance absorption occurs when the applied field is equal to 4πM+Hk . The main problem with this experiment is that of keeping the film oriented so that at least parts of it are exactly perpendicular to the applied field. A misorientation of 20 sec causes the precession frequency at H = 4πM+Hk to shift from zero to 90 Mc. This problem was overcome by using a cross modulation field.
The width of the absorption line at 2 Mc for a typical film was 22 Oe. The linewidth increased with frequency until a maximum width of 65 Oe was observed at 15 Mc. As the frequency was increased past this, the linewidth began to decrease and a number of subsidiary absorption peaks began to appear below the main line. This behavior is attributed to the roughness of the film surface.
34(1963); http://dx.doi.org/10.1063/1.1729378View Description Hide Description
Oriented (001) ironfilms deposited on MgO were examined by ferromagnetic resonance at 9.2, 18.4, and 25.0 kMc. A variation of resonance field at 18.4 and 25.0 kMc with an angle θ between the external magnetic field and the  direction in the film plane is nearly cos4θ. The crystalline anisotropy constant K 1 and the g factor of iron at 300°K are obtained as (4.90±0.10) × 105 ergs/cm3 and 2.01±0.02, respectively. At the lower frequency two resonance peaks are observed only near the 〈110〉 directions. This anomalous effect is explained by a simple single‐domain analysis.