In this paper the first nonlinear theory on ferromagnetic transmission resonance in metals is presented in detail. As in all transmission-resonance experiments, the sample forms the common wall of two microwave cavities the excitation cavity and the receiving cavity. The theory pertains to the geometry in which the static and microwave fields are mutually parallel and also parallel to the sample surface at the excitation cavity. The phenomenological theory is constructed from Maxwell's equations and the Bloch-Bloembergen equations. The sample is taken to lie in the xz plane with the static and magnetic fields along the z axis. The Mx,y equations of motion for the magnetization are linearized but not the Mz equation. In this analysis, two transmitted microwave fields through the sample are important. One is polarized along the z axis and oscillates at the applied frequency. The other, polarized along the x axis, has as its frequency half the value of the applied frequency. The theory thus predicts subharmonic generation, which we have recently observed in iron. It also shows the two transmission effects to be sensitive to the exchange stiffness constant. This is demonstrated in the following paper where the theory is compared to the experimental results for iron and nickel. The possibility is thus raised that the nonlinear effects to be described in this and the following paper can be used to determine the exchange stiffness constant and ultimately the exchange integral as a function of temperature in ferromagnetic metals and alloys.
ASJC Scopus subject areas
- Condensed Matter Physics