Magnetic anisotropy and structure of magnetic recording media (invited)

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Abstract
The recording characteristics of magnetic media depend significantly on magnetic anisotropy. We have been pursuing an investigation of anisotropy in thin-film recording media involving coordinated TEM, SEM, x-ray and electron diffraction, x-ray fluorescence, TM, VSM examinations, and, in addition, ferromagnetic resonance (FMR). In CoCr films we have shown that the magnetic constituents often are stratified magnetically and correspondingly structurally. The magnetic deconvolution of such a composite specimen by FMR is relatively straightforward; it is difficult when quasistatic torque magnetometer or vibrating sample magnetometer techniques are employed. From FMR analysis, data are obtained on the effective magnetic anisotropy field components, on the γ factor (or equivalently the g value) and on the line breadth. If the value of 4πMs is available, the effective fields can be interpreted in terms of anisotropy energy components. By integrating over the FMR lines, information relating to the relative volumes of the constituents can be obtained. Many CoCr films are dual layer films in which a disordered ‘‘transition layer’’ intervenes between the substrate and the desired or ‘‘bulk’’ region. In such films the magnetocrystalline anisotropy of the disordered layer tends to average to zero, leaving the shape anisotropy dominant. We have performed annealing procedures with and without applied magnetic fields and have correlated the changed FMR spectra with ensuing changes in anisotropy and hence structure. We have begun an investigation of magnetoelastic effects in such films by FMR techniques.