G. P. Weiss

Measured Relaxation Times for the Uniaxial‐Anisotropy Spectrum in Nonmagnetostrictive Permalloy Films

The relaxation time τ for realignment of an atomic anisotropy by 90° has been measured for a number of fast processes (τ<103 sec) occurring in nonmagnetostrictive Permalloy films. The method of measurement utilizes the magnetoresistance effect and is described in detail elsewhere. For films deposited between 23° and 200°C at 10−6 to 10−5 Torr and measured at the same temperature and pressure, three distinct processes plus two probable ones have been found, which together account for about one‐quarter of the total anisotropy. The activation energy Q and period factor τ0 which determine the relaxation time τ=τ0 exp (Q/kT) have been determined for each of these processes.

Steady‐State and Pulse Measurement Techniques for Thin Magnetic Films in the vhf‐uhf Range

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 mμsec can be resolved. Drive‐pulse calibration is accomplished unambiguously by using some of the unique switching properties of films which have uniaxial anisotropy.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 mμsec can be resolved. Drive‐pulse calibration is accomplished unambiguously by using some of the unique switching properties of films which have uniaxial anisotropy.

Anisotropy and Inversion in Permalloy Films

A phenomenological model of field-induced and oblique-incidence anisotropy in Permalloy films is proposed. It is assumed that the field-induced structure does not introduce any local spatial dispersion in the macroscopic magnetization M; the opposite is assumed for oblique-incidence structure. In addition it is assumed that the oblique-incidence dispersion is anisotropic, being least when M is perpendicular to the depositing beam.Support for the model comes from anisotropies, found for oblique-incidence films only, in the following measurements: resonance line width, transmission of polarized light, and resistivity. A primary success of the model is the prediction of a correlation between anisotropy and inversion (Hw/Hk>1). Inverted films can be made by crossing the field-induced and oblique-incidence anisotropies at 90°. Such films exhibit a “locked” state in which opposite rotation of M in local regions occurs; this implies centers of spatial dispersion and provides the connection with oblique-incidence...

Uniaxial‐Anisotropy Spectrum in Nonmagnetostrictive Permalloy Films

The uniaxial‐anisotropy spectrum in Permalloy films has been studied by: (1) deposition in H∥ on a substrate at temperature Ts, (2) annealing in either a dc field H⊥ or a circular rotating field Hr for specified time intervals, (3) quenching of the substrate holder by water‐cooled coils. Significant aspects of this procedure are: (1) annealing is carried out before exposure to air (oxygen), (2) quenching gives well‐defined annealing times, (3) each experiment involves freshly deposited samples which are in a well‐defined and reproducible state. These experiments have led to the identification of five separate contributions to the anisotropy in nonmagnetostrictive Permalloy, namely: (1) and (2) two types of contributions due to lattice vacancies with rotational activation energies≤0.2 eV and which became locked after exposure to air (oxygen), (3) and (4) two contributions with rotational activation energies∼1 eV, thought to be due to half self‐interstitials and carbon interstitials, respectively, and (5) d...

Investigations into the Origin of Anisotropy in Oblique-Incidence Films

Experimental evidence is presented which shows that the magnetic anisotropy of oblique-incidence Permalloy and iron films is not caused by an inclined texture axis or anisotropic strain. Electron diffraction and microscopy have not yet revealed anisotropy in the crystalline microstructure of these films. These techniques have also thus far failed to reveal the existence of agglomeration of the crystallites into small groups having anisotropic geometric shapes. Magnetic anisotropy, on the other hand, was observed in Permalloy films deposited at normal incidence on non-magnetic metal films deposited at oblique incidence; this would suggest such an agglomeration mechanism. There is also some indication that oxygen may play a role in oblique-incidence magnetic anisotropy.

Deposition Temperature and Compositional Dependence of Negative Anisotropy in Nickel‐Iron Films

An investigation of the deposition temperature (200° to 350°C) and compositional (80% to 87% Ni) dependence of negative anisotropy (K−) in nickel‐iron films has been made. The results indicate that the number of K− regions is zero below a critical temperature which depends on composition and increases with increasing temperature; the more negative the magnetostriction λ (λ 83), the lower the critical temperature. The following qualitative hypothesis is suggested for the origin of K− regions: It is known that deposited metal films have a real surface area much larger than the macroscopic area of the deposit. Thus the films are actually porous and mass diffusion between adjacent crystallites occurs in order to lower surface energy at the expense of strain energy. If the mass diffusion were anisotropic, for example, by depending on the direction of M, then anisotropic strain would be generated. The resulting anisotropic strain coupled to ± magnetostriction would then generate local K± (or K∓ since...

Annealing of Oblique-Incidence Permalloy Films

The anisotropy of evaporated Permalloy films (composition near zero magnetostriction) deposited on glass at 45° to the substrate normal and at a substrate temperature of 200°C has been studied after anneal for several hours at 300°C. After anneal the room temperature easy axis of films with positive magnetostriction is in the original direction. However, films with negative magnetostriction develop a new room temperature easy axis 90° to the original one; at 300°C the easy axis is in the original direction. Application of a large magnetic field in any direction during anneal does not influence the final magnetic anisotropy in either case. These effects are qualitatively explained by assuming the anneal to increase the tension along the long axis of oblique-incidence chains, a process which converts surface energy into strain energy. Anisotropy was measured by resonance in a coaxial bridge over the frequency range 50 Mc to 2100 Mc. A rectangular coaxial cavity is used which can be heated to 500°C in a vacu...