摘要:

Thin magnetic films (∼1000 A) evaporated onto a heated glass substrate in the presence of a dc magnetic field develop a uniaxial magnetic anisotropy energy of the formEk=Ksin2&phgr;, with &phgr; measured from the deposition field. Such films promise to outperform ferrite cores in digital‐computer memory‐systems by several orders of magnitude. A detailed static and dynamic theory based on the above anisotropy energy and the Landau‐Lifshitz dynamical equation is presented. The static theory contains the unique feature of the coercive force parallel to the easy axis being dependent on a field in the plane of the film and perpendicular to the easy axis. Experimental verification of the theory is given.The dynamic theory considers both steady‐state and pulse response. The steady‐state solution is well known; the pulse solution must take very careful account of all the important torques acting in a switching experiment, and numerical results are obtained by the use of a digital computer. Experimentally, steady‐state resonance is measured from 100 to 10 000 Mc and pulse switching down to 3 m&mgr;sec. Both types of experiment are in good agreement with each other and with the theory.

ISSN:0021-8979    

DOI:10.1063/1.1723097

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The magnetization reversal process of iron‐nickel films (nominally 82% Ni‐18% Fe) deposited in the presence of a magnetic field to a thickness of about 1000 A to 4000 A have been examined by the application of appropriate fields. Experimental results indicate that at least two different magnetization reversal mechanisms are effective. The first, characterized by relatively long remagnetization periods, involves domain‐wall movement; the second, characterized by relatively short remagnetization periods, is consistent with the rotation of the magnetization in the plane of the film. The threshold for the rotational process is altered by the application of transverse magnetic field in a manner consistent with a simple energy model.

ISSN:0021-8979    

DOI:10.1063/1.1723098

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The present paper analyzes a rotational model of flux reversal in ferromagnetic materials. A brief review of the experimentally established details of the flux reversal process in square loop ferrites is given. The discrepancies between the experimental results and the predictions of the domain wall motion theory are discussed. The switching coefficient,Sw, is examined in detail.The rotation model is based on the solution of the modified Landau and Lifshitz equation, but does not assume that the magnetization rotates uniformly throughout the sample. The model predicts the shape of the output voltage pulse, the relationship between the flux reversal time and the applied field, and the minimum switching coefficient that can be obtained for a given ferrite. The switching coefficients determined experimentally for ferrites, permalloy tape, and thin evaporated metal films (with zero transverse field) are within a factor of three of the minimum value ofSwpredicted by this model.

ISSN:0021-8979    

DOI:10.1063/1.1723099

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Results of an investigation of magnetic flux change in the direction perpendicular to the direction of the applied field indicate that the maximum flux in the transverse direction does not occur at the time when the sample is half reversed. From these data, taken on thin evaporated films of iron‐nickel, it is concluded that a coherent rotation theory which assumes a single magnetization vector to represent the entire sample is not adequate to explain the results. It is suggested that, when a small transverse field is present, the magnetization starts to reverse by coherent rotation but soon loses phase throughout the sample so that the reversal is completed by noncoherent rotation. With no transverse field, the coherence is never established and the reversal is completely by noncoherent rotation. Added evidence for this suggestion is presented in the form of a comparison of thin films with ferrite and Permalloy tape cores. In both the normal and transverse directions, the observations are similar, supporting the view that the reversal of films and cores is by the same general mechanism.

ISSN:0021-8979    

DOI:10.1063/1.1723100

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Iron‐nickel films depositedin vacuoin the presence of a magnetic field have been annealed in an inert environment. It has been established that, when the annealing is performed in an orienting field of 30 oe, initial magnetic properties of these films can be altered provided that the initial temperature is high enough. If a field is applied at right angles to the original preferred direction and in the plane of the film, the magnitude of the magnetic anisotropy can be reduced without changing the preferred direction; the preferred direction of magnetization can be changed if the anneal temperature is sufficiently high. This last effect confirms the observations of Williams and Sherwood.

ISSN:0021-8979    

DOI:10.1063/1.1723101

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

The magnetization of permalloy films of 0.1 to 0.3 &mgr; thickness vacuum‐deposited in a magnetic field is reversibly rotated by a pulsed external field applied at right angles to the direction of easy magnetization. The total angle of rotation is deduced from the amplitude of the detected signal or from the strength of the applied drive field. Reversible rotations of 60° or more are repeated for at least 108cy in some films. An excessive drive field results in a loss of remanent magnetization after a few rotations. High wall‐motion coercivity is a necessary but not sufficient condition for large reversible rotation angles. Films giving a large rotation tend to have open hysteresis loops in the difficult direction.

ISSN:0021-8979    

DOI:10.1063/1.1723102

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

A vhf‐uhf bridge consisting of two loops placed symmetrically in a rectangular coaxial cavity has been used to study steady‐state and pulse relaxation in thin (∼1000 A) Permalloy films. For steady‐state measurements a coaxial transformer converts the bridge output from balanced‐to‐ground to unbalanced‐to‐ground; measurements from 100 to 1500 Mc are currently possible. Pulse measurements utilize the ungrounded deflection plates of a wide‐band traveling‐wave oscilloscope; pulse response to 2 m&mgr;sec can be resolved. Drive‐pulse calibration is accomplished unambiguously by using some of the unique switching properties of films which have uniaxial anisotropy.

ISSN:0021-8979    

DOI:10.1063/1.1723103

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

A ferromagnetic film may be arbitrarily considered as ``ultra‐thin'' when its thickness is less than 100 A. It has been possible to observe microwave resonance absorption in Permalloy films down to approximately 15 A thickness. The magnetization drops sharply near 60 A, and ferromagnetism disappears between 8 A and 12 A. Line shape and width andgfactor have also been measured.

ISSN:0021-8979    

DOI:10.1063/1.1723104

出版商:AIP    

年代:1958

数据来源: AIP

摘要:

Domain‐wall structure in Permalloy films in the thickness range 25 to 2000 A has been studied by the Bitter technique. A new type of 180° wall has been observed: the main wall is cut at regular intervals by short, right‐angle ``cross ties'' which terminate in free, single ends. The cross‐tie period and length are dependent on film thickness, each becoming shorter with decreasing thickness. These patterns can be understood in terms of a new model for the structure of domain walls in thin films of low‐anisotropy material. In the conventional model the atomic moments within the wall rotate about an axis perpendicular to the wall. In a thin film such a configuration leads to a large energy contribution from the large demagnetization factor normal to the film. In the new model, the axis of rotation is itself thought to rotate about the axis of the wall to give a ``corkscrew'' configuration of spins and a large decrease in associated magnetostatic energy. Of several experiments which have been performed which support this model, one is briefly described.

ISSN:0021-8979    

DOI:10.1063/1.1723105

出版商:AIP    

年代:1958

数据来源: AIP

ISSN:0021-8979    

DOI:10.1063/1.1723106

出版商:AIP    

年代:1958

数据来源: AIP